Search

The kinetic mixing (KM) portal, by which the Standard Model (SM) photon mixes with a light dark photon arising from a new $U(1)_D$ gauge group, allows for the possibility of viable scenarios of sub-GeV thermal dark matter (DM) with appropriately suppressed couplings to the SM. This KM can only occur if particles having both SM and dark quantum numbers, here termed portal matter (PM), also exist. The presence of such types of states and the strong suggestion of a need to embed $U(1)_D$ into a non-abelian gauge structure not too far above the TeV scale based on the RGE running of the $U(1)_D$ gauge coupling is potentially indicative of an enlarged group linking together the visible and dark sectors. The gauge group $G=SU(3)_c\times SU(3)_L\times U(1)_A\times U(1)_B=3_c3_L1_A1_B$ is perhaps the simplest setup wherein the SM and dark interactions are partially unified in a non-abelian fashion that is not a simple product group of the form $G=G_{SM}\times G_D$ encountered frequently in earlier work. The present paper describes the implications and phenomenology of this type of setup., Comment: 33 pages, 8 figs; Refs. added

Portal Matter, with both SM and dark charges, induces KM between the $U(1)_D$ dark photon and the SM gauge fields offering an attractive mechanism by which light thermal DM can obtain its observed relic density. If DM is fermionic, the CMB informs us that it must be Majorana/pseudo-Dirac in nature to avoid temperature-independent $s$-wave annihilation to SM states. How does this fit into a more complete picture with the SM? A first step along this path may not lie far away in energy due to the RGE running of the dark gauge coupling which can becomes non-perturbative before the $\sim 10$'s of TeV range. This implies that $U(1)_D$ must become embedded in a non-Abelian group, $G_D$, before this occurs. The breaking of this group then produces the PM masses and the heavy gauge fields associated with $G_D$ lead to new interactions between the SM and the dark sector. In the past we have examined a set of distinctive phenomenological features associated with this setup, based upon a number of simplifying assumptions. It behooves us to explore the impact of these assumptions on the predictions for possible experimental tests of these models. In past analyses we assumed that DM is a VL, complex singlet under $G_D$. If this assumption is relaxed, the dark sector must be augmented by additional fermion(s) and the scalar fields needed to break the symmetries while generating the needed Majorana-like mass terms for the DM. Here we analyze the simplest extension of this kind wherein the DM lies in a VL doublet of $G_D$, which we take to have the structure $SU(2)_I\times U(1)_{Y_I}$, leading to new phenomenology. We find that given the current LHC search constraints on the masses of heavy gauge bosons, the production of these new dark states with large rates is unlikely at colliders unless they are produced singly in $gg$-fusion or are resonantly enhanced., Comment: 26 pages, 6 figs; text and refs updated

Kinetic mixing of the dark photon, the gauge boson of a hidden $U(1)_D$, with the Standard Model (SM) gauge fields to induce an interaction between ordinary matter and dark matter (DM) at 1-loop requires the existence of portal matter (PM) fields having both dark and SM charges. As discussed in earlier work, these same PM fields can also lead to other loop-level mechanisms besides kinetic mixing that can generate significant interactions between SM fermions and the dark photon in a manner analogous to those that can be generated between a Dirac neutrino and a SM photon, \ie, dark moments. In either case, there are reasons to believe, \eg, due to the RGE running of the $U(1)_D$ gauge coupling, that PM fields may have $\sim$ TeV-scale masses that lie at or above those directly accessible to the HL-LHC. If they lie above the reach of the HL-LHC, then the only way to possibly explore the physics at this high scale in the short term is via indirect measurements made at lower energies, \eg, at lepton colliders operating in the $m_Z$ to 1 TeV range. In particular, processes such as $e^+e^- \to \gamma+$DM or $e^+e^-\to \bar ff$, where $f$ is a SM fermion, may be most useful in this regard. Here we explore these possibilities within the framework of a simple toy PM model, introduced in earlier work, based on a non-abelian dark gauge group completion operating at the PM scale. In the KM setup, we show these efforts fail due to the inherently tiny cross sections in the face of substantial SM backgrounds. However, in the case of interactions via induced dark moments, since they necessarily take the form of higher dimensional operators whose influence grows with energy, we show that access to PM-scale information may become possible for certain ranges of the toy model parameters for both of these $e^+e^-$ processes at a 1 TeV collider., Comment: 32 pages, 13 figs; discussion added

As is well-known, Trinification, \ie, the extension of the Standard Model (SM) to $[SU(3)]^3=SU(3)_c\times SU(3)_L\times SU(3)_R$ as occurs in $E_6$ models, allows for a partial unification of the gauge forces even though quarks and leptons remain in separate multiplets so that no heavy gauge or scalar fields exist which can generate proton decay. The extension of this idea to Quartification, by including an additional $SU(3)'$ factor, has also been considered in the literature maintaining the basic attributes of Trinification but now allowing, \eg, for a more symmetric treatment of quarks and leptons at the price of new matter fields and gauge interactions. In this paper, we will consider this $SU(3)'$ to be the `dark' gauge group, now containing the familiar $U(1)_D$ subgroup, under which the SM fields are all neutral, which is associated with kinetic mixing (KM) and the existence of a light, $\lsim 1 $ GeV dark photon. This setup naturally predicts the existence of color-singlet portal matter (PM) fields, carrying both electromagnetic and $U(1)_D$ dark charges, that are necessary to generate this KM at the 1-loop level and whose masses are directly tied with those of the many new gauge bosons that originate from the extended gauge sector. In this paper, after a discussion of the detailed structure of this model, we present a broad survey of the collider phenomenology of the large set of new fields that must necessarily arise from this setup in a simplified version involving only a single generation of fermions. We demonstrate that several new signatures may be anticipated at the LHC as well as at future hadron and lepton colliders if such models are realized in nature., Comment: 33 pages, 7 Figs; text augmented and ref. added

The kinetic mixing (KM) of a dark photon (DP) with the familiar one of the Standard Model (SM) requires the existence of a new set of fields, called portal matter (PM), which carry both SM and dark sector quantum numbers, some whose masses may lie at the TeV scale. In the vanilla KM model, the dark gauge group is just the simple $G_{Dark}=U(1)_D$ needed to describe the DP while the SM gauge interactions are described by the usual $G_{SM}=SU(3)_c\times SU(2)_L\times U(1)_Y$. However, we need to go beyond this simple model to gain a better understanding of the interplay between $G_{SM}$ and $G_{Dark}$ and, in particular, determine how they both might fit into a more unified construction. Following our previous analyses, this generally requires $G_{Dark}$ to be extended to a non-abelian group, \eg, $SU(2)_I\times U(1)_{Y_I}$, under which both the PM and SM fields may transform non-trivially. In this paper, also inspired by our earlier work on top-down models, we consider extending the SM gauge group to that of the Left-Right Symmetric Model (LRM) and, in doing so, through common vacuum expectation values, link the mass scales associated with the breaking of $G_{Dark}\to U(1)_D$ and the PM fields to that of the RH-neutrino as well as the heavy gauge bosons of the LRM. This leads to an interesting interplay between the now coupled phenomenologies of both visible and dark sectors at least some of which may be probed at, \eg, the LHC and/or at the future FCC-hh., Comment: 28 pages, 6 figs; text updated, refs and fig added

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection., Comment: 108 pages + 38 pages references and appendix, 37 figures, Report of the Topical Group on Beyond the Standard Model Physics at Energy Frontier for Snowmass 2021. The first nine authors are the Conveners, with Contributions from the other authors

If dark matter (DM) interacts with the Standard Model (SM) via the $U(1)_D$ kinetic mixing (KM) portal at low energies, it necessitates not only the existence of portal matter (PM) particles which carry both dark and SM quantum numbers, but also a possible UV completion into which this $U(1)_D$ and the SM are both embedded. In earlier work, following a bottom-up approach, we attempted to construct a more unified framework of these SM and dark sector interactions. In this paper we will instead begin to explore, from the top-down, the possibility of the unification of these forces via the decomposition of a GUT-like group, $G\to G_{SM}\times G_{Dark}$, where $U(1)_D$ is now a low energy diagonal subgroup of $G_{Dark}$ and where the familiar $G_{SM}=SU(5)$ will play the role of a proxy for the conventional $SU(3)_c\times SU(2)_L\times U(1)_Y$ SM gauge group. In particular, for this study it will be assumed that $G=SU(N)$ with $N=6-10$. Although not our main goal, models that also unify the three SM generational structure within this same general framework will also be examined. The possibilities are found to be quite highly constrained by our chosen set of model building requirements which are likely too strong when they are employed simultaneously to obtain a successful model framework., Comment: 27 pages, 1 figure; text and references updated

The kinetic mixing (KM) portal is a popular mechanism which allows light dark matter (DM) in the mass range below $\sim 1$ GeV to achieve the observed relic density by thermal means and can be effectively described by only a few parameters, e.g., $\epsilon$, the strength of this KM. In the simplest setup, the Standard Model (SM) $U(1)_Y$ hypercharge gauge boson and a $U(1)_D$ dark photon (DP), which only couples to fields in the dark sector, experience KM via loops of portal matter (PM) fields which have both SM and dark charges thus generating a small coupling between us and dark matter (DM). However, if one wishes to understand the underlying physics behind this idea in a deeper fashion we need to take a step upward to a more UV-complete picture. Meanwhile, CDFII has measured a value for the $W$-boson mass which lies significantly above SM expectations. In this paper we speculate that this shift in the $W$'s mass may be related to the $\sim 1$ GeV mass of the DP within a framework of scalar PM that leads to phenomenologically interesting values of $\epsilon$ via non-abelian KM due to the existence of an $SU(2)_L$, $Y=0$, {\it complex} Higgs triplet which carries a non-zero value of the $U(1)_D$ dark charge. Possible gauge boson plus missing energy signatures of this scenario that can appear at the LHC and elsewhere are examined. Indeed, with modest assumptions, all of the new scalar PM states are predicted to have masses below roughly $\simeq 630$ GeV and so should be at least kinematically accessible. The HL-LHC will very likely to be able to explore all of this model's allowed parameter space., Comment: 21 pages, 6 figs, text and refs added

If dark matter (DM) interacts with the Standard Model (SM) via the kinetic mixing (KM) portal, it necessitates the existence of massive, likely $\gsim 1$ TeV, enabler portal matter (PM) particles that carry both dark and SM quantum numbers which will appear in vacuum polarization-like loop graphs. Such heavy states are only directly accessible at high energy colliders and apparently lie at mass scales beyond the direct kinematic reach of the ILC, CEPC and FCC-ee. A likely possibility is that these new particles are part of the 'next step' toward a UV-complete scenario describing both the SM and dark sector physics. A simple and straightforward example of such a scenario involving a non-abelian dark sector gauge group is employed in this work to demonstrate some of the range expected from this new physics. Here we present a broad survey of existing analyses designed to explore the nature of such PM states in a array of collider contexts, particularly at the LHC, and point out some of the future directions where additional work is obviously required in the hunt for new signatures as well as in model building directions., Comment: Contribution to Snowmass; 35 pages, 18 figs; text and figure updated

We present a proposal for a cold copper distributed coupling accelerator that can provide a rapid route to precision Higgs physics with a compact 8 km footprint. This proposal is based on recent advances that increase the efficiency and operating gradient of a normal conducting accelerator. This technology also provides an $e^{+}e^{-}$ collider path to physics at multi-TeV energies. In this article, we describe our vision for this technology and the near-term R&D program needed to pursue it., Comment: 34 pages, 8 figures, Contribution to Snowmass 2021. The editors can be contacted at the following addresses: mib@slac.stanford.edu, nanni@slac.stanford.edu, mpeskin@slac.stanford.edu, caterina@slac.stanford.edu

As experimental searches for WIMP dark matter continue to yield null results, models beyond the WIMP paradigm have proliferated in order to elude ever improving observational constraints, among them that of sub-GeV dark matter mediated by a massive vector portal (a dark photon) associated with a new dark $U(1)$ gauge symmetry. It has been previously noted that for a significant range of the parameter space of this class of models, the annihilation of dark matter particles into a pair of dark photons can dominate the freeze-out process even when this process is kinematically forbidden for dark matter at rest -- this is known as the "forbidden dark matter" (FDM) regime. Prior studies of this regime, however, assume that any "dark Higgs" associated with breaking the dark $U(1)$ and imparting mass to the dark photon is decoupled from the dark matter and as such plays no role in the freeze-out process. In this paper, we explore the effects of a dark Higgs on sub-GeV dark matter phenomenology in this FDM regime by considering the simplest possible construction in which there exist non-trivial dark matter-dark Higgs couplings: a model with a single complex scalar DM candidate coupled directly to the dark Higgs field. We find that for a wide range of parameter space, the dark Higgs can alter the resulting relic abundance by many orders of magnitude, and that this effect can remain significant even for a small dark matter-dark Higgs coupling constant. Considering measurements from direct detection and measurements of the CMB, we further find that points in this model's parameter space which recreate the appropriate dark matter relic abundance suffer only mild constraints from other sources at present, but may become accessible in near-future direct detection experiments., Comment: 28 pages + references, 13 figures, v3: Discussions and new plots of experimental constraints added, version accepted to JHEP

If dark matter (DM) interacts with the Standard Model (SM) via the kinetic mixing (KM) portal, it necessitates the existence of portal matter (PM) particles which carry both dark and SM quantum numbers that will appear in vacuum polarization-like loop graphs. In addition to the familiar $\sim e\epsilon Q$ strength, QED-like interaction for the dark photon (DP), in some setups different loop graphs of these PM states can also induce other coupling structures for the SM fermions that may come to dominate in at least some regions of parameter space regions and which can take the form of `dark' moments, eg, magnetic dipole-type interactions in the IR, associated with a large mass scale, $\Lambda$. In this paper, motivated by a simple toy model, we perform a phenomenological investigation of a possible loop-induced dark magnetic dipole moment for SM fermions, in particular, for the electron. We show that at the phenomenological level such a scenario can not only be made compatible with existing experimental constraints for a significant range of correlated values for $\Lambda$ and the dark $U(1)_D$ gauge coupling, $g_D$, but can also lead to quantitatively different signatures once the DP is discovered. In this setup, assuming complex scalar DM to satisfy CMB constraints, parameter space regions where the DP decays invisibly are found to be somewhat preferred if PM mass limits from direct searches at the LHC and our toy model setup are all taken seriously. High precision searches for, or measurements of, the $e^+e^- \to \gamma +{\rm DP}$ process at Belle II are shown to provide some of the strongest future constraints on this scenario., Comment: 24 pages, 8 Figs; discussion modified, figure updated, refs added, more typos removed

The possibility of light dark matter (DM) annihilating through a dark photon (DP) which kinetically mixes (KM) with the Standard Model (SM) hypercharge field is a very attractive scenario. For DM in the interesting mass range below $\sim 1$ GeV, it is well known that bounds from the CMB provide a very strong model building constraint forcing the DM annihilation cross section to be roughly 3 orders of magnitude below that needed to reproduce the observed relic density. Under most circumstances this removes the possibility of an $s$-wave annihilation process for DM in this mass range as would be the case, e.g., if the DM were a Dirac fermion. In an extra-dimensional setup explored previously, it was found that the $s$-channel exchange of multiple gauge bosons could simultaneously encompass a suppressed annihilation cross section during the CMB era while also producing a sufficiently large annihilation rate during freeze-out to recover the DM relic density. In this paper, we analyze more globally the necessary requirements for this mechanism to work successfully and then realize them within the context of a simple model with two `dark' gauge bosons having masses of a similar magnitude and whose contributions to the annihilation amplitude destructively interfere. We show that if the DM mass threshold lies appropriately in the saddle region of this destructive interference between the two resonance humps it then becomes possible to satisfy these requirements simultaneously provided several ancillary conditions are met. The multiple constraints on the parameter space of this setup are then explored in detail to identify the phenomenologically successful regions., Comment: 26 pages, 12 figs; figure and discussion added, typos removed

In this paper, we present a model which attempts to unify a new dark sector force with a local $SU(3)$ flavor symmetry. Dark Matter (DM) and its potential interactions with the Standard Model (SM) continue to present a rich framework for model building. In the case of thermal DM of a mass between a few MeV and a few GeV, a compelling and much-explored framework is that of a dark photon/vector portal, which posits a new $U(1)$ "dark photon" which only couples to the SM via small kinetic mixing (KM) with the SM hypercharge. This mixing can be mediated at the one-loop level by portal matter (PM) fields which are charged under both the dark $U(1)$ and the SM gauge group. In earlier work, one of the authors has noted that models with appropriate portal matter content to produce finite and calculable kinetic mixing can arise from non-minimal dark sectors, in which the dark $U(1)$ is a subgroup of a larger gauge symmetry under which SM particles might have non-trivial representations. We expand on this idea here by constructing a model in which in which the dark $U(1)$ is unified with another popular extension to the SM gauge group, a local $SU(3)$ flavor symmetry. The full dark/flavor symmetry group is $SU(4)_F \times U(1)_F$, incorporating the local $SU(3)$ flavor symmetry with PM appearing as a vector-like "fourth generation" to supplement the three generations of the SM. To ensure finite contributions to KM, the SM gauge group is arranged into Pati-Salam multiplets. The new extended dark gauge group presents a variety of interesting experimental signatures, including non-trivial consequences of the flavor symmetry being unified with the dark sector., Comment: 53 pages plus references, 8 figures. v4: Some discussions added

The nature of dark matter (DM) and how it might interact with the particles of the Standard Model (SM) is an ever-growing mystery. It is possible that the existence of new `dark sector' forces, yet undiscovered, are the key to solving this fundamental problem. In this paper, we construct a model in which a dark photon mediates interactions with the SM via kinetic mixing. Unlike traditional models, in which the dark photon, which couples to a dark charge, $Q_D$, mixes with the hypercharge boson, our model effectively mixes the dark photon directly with the photon after electroweak symmetry is broken, but remains unmixed until the symmetry breaks. The kinetic mixing is generated at one loop by fields which satisfy $\sum Q_D Q_{em} = 0$, a condition which guarantees a finite result at one loop. In the literature, this has been traditionally obtained via heavy fermions, which may lie out of the reach of current accelerators. In this model, by contrast, this process is mediated by scalar `portal matter' fields, which are charged under the $SU(2)_L \times U(1)_Y$ of the standard model as well as the dark gauge group $U(1)_D$ and acquire GeV-scale vevs which give mass to the dark Higgs and dark photon. The additional scalar fields are relatively light, at or below the weak scale, yet may remain undetected by current experiments since their couplings to SM fermions come only through percent level mixing with the SM Higgs. At colliders, these models are typified by relatively low MET due the BSM states decaying into MET and SM bosons, with MET which is balanced by the decay of the associated production object. Nevertheless, the higher statistics of HL-LHC may be able to probe the entirety of the model space., Comment: 32 pages, 16 figures

Data from Planck measurements of the cosmic microwave background (CMB) place important constraints on models with light dark matter (DM) and light mediators especially when both lie in the mass range below $\sim 1 $ GeV. In models involving kinetic mixing where the dark photon acts as the mediator, these constraints are easily satisfied and the appropriate DM relic density achievable if the DM is, e.g., a complex scalar, where $p$-wave annihilation occurs, or is the lighter component of a split pseudo-Dirac state where co-annihilation dominates. In both of these cases, although higher order in the dark gauge coupling, $g_D$, the corresponding annihilation processes including dark photon initial state radiation (ISR) will be dominantly $s$-wave with essentially temperature independent cross sections. The rates for these dark ISR associated processes, though not yielding cross sections large enough to contribute to the relic density, can still run into possible conflicts with the bounds arising from the CMB. In this paper we perform a preliminary study of the present and potential future constraints that the CMB imposes on the parameter spaces for both of these scenarios due to the existence of this dark ISR. Further analyses of the effects of dark ISR in DM annihilation is clearly warranted., Comment: 19 pages, 7 figs; Reference added, minor text changes

Extra dimensions have proven to be a very useful tool in constructing new physics models. In earlier work, we began investigating toy models for the 5-D analog of the kinetic mixing/vector portal scenario where the interactions of dark matter, taken to be, e.g., a complex scalar, with the brane-localized fields of the Standard Model (SM) are mediated by a massive $U(1)_D$ dark photon living in the bulk. These models were shown to have many novel features differentiating them from their 4-D analogs and which, in several cases, avoided some well-known 4-D model building constraints. However, these gains were obtained at the cost of the introduction of a fair amount of model complexity, e.g., dark matter Kaluza-Klein excitations. In the present paper, we consider an alternative setup wherein the dark matter and the dark Higgs, responsible for $U(1)_D$ breaking, are both localized to the 'dark' brane at the opposite end of the 5-D interval from where the SM fields are located with only the dark photon now being a 5-D field. The phenomenology of such a setup is explored for both flat and warped extra dimensions and compared to the previous more complex models., Comment: 35 pages+ references, 19 figures. v3: some additional discussions added

The nature of dark matter (DM) and how it might interact with the particles of the Standard Model (SM) is one of greatest mysteries currently facing particle physics, and addressing these issues should provide some understanding of how the observed relic abundance was produced. One widely considered production mechanism, a weakly interacting massive particle (WIMP) produced as a thermal relic, provides a target cross section for DM annihilation into SM particles by solving the Boltzmann equation. In this thermal freeze-out mechanism, dark matter is produced in thermal equilibrium with the SM in the early universe, and drops out of equilibrium to its observed abundance as the universe cools and expands. In this paper, we study the impact of a generalized thermodynamics, known as Tsallis statistics and governed by a parameter $q$, on the target DM annihilation cross section. We derive the phase space distributions of particles in this generalized statistical framework, and check their thermodynamic consistency, as well as analyzing the impact of this generalization on the collisional term of the Boltzmann equation. We consider the case of an initial value of $q_0>1$, with $q$ relaxing to 1 as the universe expands and cools, and solve the generalized Boltzmann numerically for several benchmark DM masses, finding the corresponding target annihilation cross sections as a function of $q_0$. We find that as $q$ departs from the standard thermodynamic case of $q=1$, the collisional term falls less slowly as a function of $x = m_\chi/T$ than expected in the standard case. We also find that the target cross section falls sharply from $\sigma v \simeq 2.2-2.6\times10^{-26} \textrm{cm}^3/\textrm{s}$ for $q_0=1$ to, for example, $\sigma v \simeq 3\times 10^{-34} \textrm{cm}^3/\textrm{s}$ for $q_0=1.05$ for a 100 GeV WIMP., Comment: 19 pages, 9 figures

We propose a model of quark flavor based on an additional $SU(2)\times U(1)$ local symmetry in a warped extra dimensional bulk. In contrast to other works, we break the additional gauge symmetry in the bulk via two complex scalars which acquire bulk vevs, rather than relying on brane-localized symmetry breaking. A gauge-covariant Kaluza-Klein decomposition of a theory with a bulk spontaneously broken gauge symmetry is performed, and exact expressions for the bulk profiles of all physical particles in such systems are given. The SM quark masses and mixings are then recreated using gauge-covariant bulk quark mass terms and Yukawa-like couplings to the new bulk scalars. A numerical sampling of points in the model parameter space that recreate the quark masses and mixings is performed at a KK scale of $M_{KK} =5$ TeV. We then compute the $\Delta F = 2$ 4-quark operators arising from our new flavor gauge bosons and scalars, and those arising from Kaluza-Klein modes of SM gauge bosons. By decoupling one of our bulk scalar fields to all quark fields except the right-handed up-like sector, we find that it is possible to greatly suppress tree-level contributions to the highly constrained Kaon mixing parameters. Instead, the dominant constraints on the model emerge from neutral $B_d$ and $D$ meson mixing. These constraints are explored with our numerical sampling of the model parameter space, and the specific contribution of the new flavor gauge bosons and scalars is discussed. We find that for a significant range of realistic flavor gauge couplings, the new gauge bosons compete with the normally dominant gluon flavor-changing currents, but flavor-changing operators emerging from the bulk scalar fields are highly suppressed. Finally, we briefly comment on flavor constraints that are independent of the flavor gauge sector arising from the $Z \bar{b}_L b_L$ coupling and rare top decays., Comment: 84 pages+ references, 17 figures

The nature of dark matter (DM) and how it might interact with the particles of the Standard Model (SM) is an ever-growing mystery. It is possible that the existence of new `dark sector' forces, yet undiscovered, are the key to solving this fundamental problem, and one might hope that in the future such forces might even be `unified' with the ones we already know in some UV-complete framework. In this paper, following a bottom-up approach, we attempt to take the first steps in the construction of such a framework. The much-discussed possibility of the kinetic mixing (KM) of the `dark photon' with the hypercharge gauge boson of the SM via loops of portal matter (PM) fields, charged in both sectors, offers an attractive starting point for these efforts. Given the anticipated finite strength of the KM in a UV-complete theory, the absence of anomalies, and the lifetime constraints on the PM fields arising from CMB and nucleosynthesis constraints, PM must behave as vector-like copies of the known SM fermion fields, such as those which appear naturally in $E_6$-type models. Within such a setup, the SM and their corresponding partner PM fields would be related by a new $SU(2)_I$ gauge symmetry. With this observation as a springboard, we construct a generalization of these ideas where $SU(2)_I$ is augmented by an additional $U(1)_{I_Y}$ factor so that the light dark photon is the result of a symmetry breaking analogous to the SM, \ie, $SU(2)_I\times U(1)_{I_Y}\to U(1)_D$, but with $U(1)_D$ now also broken at the $\lesssim$ GeV scale. While SM fields are $U(1)_D$ singlets, as in the conventional dark photon approach, they transform nontrivially under the full $SU(2)_I\times U(1)_{I_Y}$ gauge group. This approach leads to numerous interesting signatures, both at low energies and at colliders, and can be viewed as an initial step in the construction of a more UV-complete framework., Comment: 35 pages, 14 figures

This paper explores the physics reach of the proton-proton Future Circular Collider (FCC-hh) and of the High-Energy LHC (HE-LHC) for searches of new particles produced in the $s$-channel and decaying to two high-energy leptons, jets (non-tops), tops or W/Z bosons. We discuss the expected discovery potential and exclusion limits for benchmark models predicting new massive particles that result in resonant structures in the invariant mass spectrum. We also present a detailed study of the HE-LHC potential to discriminate among different models, for a $Z'$ that could be discovered by the end of High-Luminosity LHC (HL-LHC)., Comment: 34 pages, 16 figures

In this paper we show that the interaction between new light dark matter mediators and the SM particles can be naturally suppressed if one employs a single, flat extra dimension (ED). In this setup, the SM fields are localized in a finite width `fat' brane, similar to models of Universal Extra Dimensions (UED), while DM, in turn, is confined to a thin brane at the opposite end of the ED interval. Including brane localized kinetic terms on the fat brane for the mediator fields, the resulting coupling between the SM and these light mediators can be several orders of magnitude smaller than the corresponding ones between the mediators and DM which we assume to be a typical gauge coupling. We investigate the implications of this scenario for both vector (i.e., dark photon, DP) and scalar mediator fields in the 5-D bulk. In this setup kinetic mixing, which is usually employed to suppress light mediator couplings, is not required. Here we assume that the SM particles couple to the DP via their $B-L$ charges while the DP couples to the DM via a dark charge. Both the vector DP couplings and the corresponding Higgs portal couplings with the SM are shown to be natural small in magnitude with a size dependent on ratio of the 5-D compactification radius, $R^{-1} \sim 0.1-1$ GeV, and the SM brane thickness, $L^{-1} \sim 2-10$ TeV, a range chosen to avoid LHC and other experimental constraints. In this framework one can obtain the observed value of the DM relic abundance for a wide range of parameter choices, while the constrains due to direct DM detection and the invisible width of the Higgs do not impose significant challenges to the model. Finally, this mechanism can lead to distinct signatures in both present and upcoming experiments as it combines some common features of UED and DP models in a single ED setup., Comment: 25 pages, 10 figures, version accepted for publication JHEP

Dark photons (DP) are interesting as potential mediators between the dark matter (DM) sector and the fields of the Standard Model (SM). The interaction of the DP, described by a broken $U(1)_D$ gauge symmetry, with the SM is usually generated at the one-loop level via kinetic mixing through the existence of portal matter (PM), here assumed to be fermionic, which carries both a dark charge as well as a SM $U(1)_Y$ hypercharge. For theoretical consistency, as well as for many phenomenological reasons, this PM must be vector-like with respect to the SM and dark gauge groups and, in particular, is shown to be allowed only to transform as vector-like copies of the usual SM fields. The dark Higgs that is responsible for the breaking of $U(1)_D$ can then generate a mixing between the PM and SM fields with the same electric charge thus altering the DP interactions with (at least some of) the SM fields and also providing a path for the PM fields to decay. In this paper we briefly explore the phenomenology of some specific simple models of this PM including, for the case where the PM is leptonic in nature, their potential impact on experiments probing low energy parity-violation and the g-2 of the muon. In the case of color-triplet, bottom quark-like PM, their direct pair- and single-production at the LHC is shown to be observable in final states that include missing $E_T$ and/or very highly boosted lepton-jets together with pairs of high $p_T$ b-jets that can be used to trigger on such events. These signatures are quite distinct from those usually employed in the search for vector-like quarks at the LHC and, furthermore, we demonstrate that the conventional signal channels for vector-like quarks involving the SM Higgs and gauge fields are essentially closed in the case of PM., Comment: 26 pages, 9 figs; discussion updated, figure added

Extra dimensions can be very useful tools when constructing new physics models. Previously, we began investigating toy models for the 5-D analog of the kinetic mixing/vector portal scenario where the interactions of bulk dark matter with the brane-localized fields of the Standard Model are mediated by a massive $U(1)_D$ dark photon also living in the bulk. In that setup, where the dark matter was taken to be a complex scalar, a number of nice features were obtained such as $U(1)_D$ breaking by boundary conditions without the introduction of a dark Higgs field, the absence of potentially troublesome SM Higgs-dark singlet mixing, also by boundary conditions, the natural similarity of the dark matter and dark photon masses and the decoupling of the heavy gauge Kaluza-Klein states from the Standard Model. In the present paper we extend this approach by examining the more complex cases of Dirac and Majorana fermionic dark matter. In particular, we discuss a new mechanism that can occur in 5-D (but not in 4-D) that allows for light Dirac dark matter in the $\sim 100$ MeV mass range, even though it has an $s$-wave annihilation into Standard Model fields, by avoiding the strong constraints that arise from both the CMB and 21 cm data. This mechanism makes use of the presence of the Kaluza-Klein excitations of the dark photon to extremize the increase in the annihilation cross section usually obtained via resonant enhancement. In the Majorana dark matter case, we explore the possibility of a direct $s$-channel dark matter pair-annihilation process producing the observed relic density, due to the general presence of parity-violating dark matter interactions, without employing the usual co-annihilation mechanism which is naturally suppressed in this 5-D setup., Comment: 22 pages, 7 Figs; discussions and refs. added, typos fixed; title changed to match earlier work

Extra dimensions provide a unique tool for building new physics models. Here we extend the kinetic mixing/dark photon mediator scenario for the case of complex scalar dark matter interacting with the Standard Model to 5-D. We assume that the inverse size of the new, flat extra dimension is $\sim 10 - 1000$ MeV, the mass range of interest in numerous current experiments, and discuss the resulting phenomenology. Here we see that 5-D constructions can be used to soften some of the possible tuning issues which are sometimes encountered in the corresponding 4-D models., Comment: 6 pages, Moriond 2018 EWK proceedings

Model building within the Randall-Sundrum (RS) framework generally involves placing the Standard Model fields in the bulk. Such fields may possess non-zero values for their associated brane-localized kinetic terms (BLKTs) in addition to possible bulk mass parameters. In this paper we clearly identify the regions of the RS model parameter space where the presence of bulk mass terms and BLKTs yield a setup which is free from both ghost and tachyon instabilities. Such physically acceptable parameter space regions can then be used to construct realistic and phenomenologically viable RS models., Comment: Latex, 30 pages, 2 figures

Extra dimensions (ED) can provide a useful tool for model-building. In this paper we introduce a single, flat ED extension of the kinetic-mixing/dark photon (DP) portal for dark matter (DM) interactions with the Standard Model (SM) assuming a compactification `radius' of order $R^{-1}\sim10-1000$ MeV and examine the resulting modifications to and augmentation of the usual DP phenomenology. In the present scenario, both the DP and DM experience the full 5-D while the SM fields are constrained to lie on a 4-D brane at the boundary of the ED. Such a setup can naturally yield the observed value of the DM relic density and explain the required rough degeneracy of the DM and DP masses needed to obtain it. Gauge symmetry breaking can occur via boundary conditions without the introduction of an additional singlet Higgs scalar thus avoiding all constraints associated with the coupling of such a field to the usual SM Higgs field in 5-D. The self-consistency of the field redefinitions that map the gauge fields into a canonical basis and thus removing the kinetic mixing terms is found to lead to a strong model building constraint on the ED setup involving a brane localized kinetic term for the 5-D gauge field on the SM brane. Multiple variations of this scenario are found to be possible which are consistent with all current experimental constraints but which predict very different phenomenologies. In this paper, after setting up the general model formalism, we discuss in detail the case of a complex scalar 5-D DM field, consistent with constraints arising from the CMB, which may or may not obtain a vacuum expectation value (vev). The resulting Kaluza-Klein (KK) towers of both the DM and DP fields are found to yield interesting and distinctive signatures., Comment: 44 pages,13 figs; discussion, figure and references updated, typos fixed; title changed for journal

Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, $\left< \sigma v \right>$, which are consistent with the observed relic abundance in the case of spin-1 dark matter. We examine constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments., Comment: 33 pages, 8 figures; added references and fixed minor typos

The elucidation of the nature of new phenomena requires a multi-pronged approach to understand the essential physics that underlies it. As an example, we study the simplified model containing a new scalar singlet accompanied by vector-like quarks, as motivated by the recent diphoton excess at the LHC. To be specific, we investigate three models with $SU(2)_L$-doublet, vector-like quarks with Yukawa couplings to a new scalar singlet and which also couple off-diagonally to corresponding Standard Model fermions of the first or third generation through the usual Higgs boson. We demonstrate that three classes of searches can play important and complementary roles in constraining this model. In particular, we find that missing energy searches designed for superparticle production, supply superior sensitivity for vector-like quarks than the dedicated new quark searches themselves., Comment: References added; small bug found in model and analysis implementation, numerical results slightly modified, conclusions unchanged

A possible explanation of the excesses observed by ATLAS in the Z+jets+MET channel within the p(henomenological)MSSM is discussed. We have found that the cascade of first/second generation squarks to binos to Higgsino LSPs, with judiciously chosen sparticle masses, can provide a viable scenario that is consistent with all other experimental constraints., Comment: Talk given at Rencontres de Moriond 2016, Electroweak Interactions and Unified Theories, 12-19 March 2016, LaThuile, Italy

We examine the scenario of a warped extra dimension containing bulk SM fields in light of the observed diphoton excess at 750 GeV. We demonstrate that a spin-2 graviton whose action contains localized kinetic brane terms for both gravity and gauge fields is compatible with the excess, while being consistent with all other constraints. The graviton sector of this model contains a single free parameter, once the mass of the graviton is fixed. The scale of physics on the IR-brane is found to lie in the range of a $\sim$ few TeV, relevant to the gauge hierarchy. There remains significant flexibility in the coupled gauge/fermion KK sectors to address the strong constraints arising from precision measurements., Comment: Corrected and improved analysis. 6 pages, 3 figures

We examine the `diboson' excess at $\sim 2$ TeV seen by the LHC experiments in various channels. We provide a comparison of the excess significances as a function of the mass of the tentative resonance and give the signal cross sections needed to explain the excesses. We also present a survey of available theoretical explanations of the resonance, classified in three main approaches. Beyond that, we discuss methods to verify the anomaly, determining the major properties of the various surpluses and exploring how different models can be discriminated. Finally, we give a tabular summary of the numerous explanations, presenting their main phenomenological features., Comment: 37 pages, 9 Figures, 1 Table

We investigate the sensitivity of the next generation of flavor-based low-energy experiments to probe the supersymmetric parameter space in the context of the phenomenological MSSM (pMSSM), and examine the complementarity with direct searches for Supersymmetry at the 13 TeV LHC in a quantitative manner. To this end, we enlarge the previously studied pMSSM parameter space to include all physical non-zero CP-violating phases, namely those associated with the gaugino mass parameters, Higgsino mass parameter, and the tri-linear couplings of the top quark, bottom quark and tau lepton. We find that future electric dipole moment and flavor measurements can have a strong impact on the viability of these models even if the sparticle spectrum is out of reach of the 13 TeV LHC. In particular, the lack of positive signals in future low-energy probes would exclude values of the phases between ${\cal O}(10^{-2})$ and ${\cal O}(10^{-1})$. We also find regions of parameter space where large phases remain allowed due to cancellations. Most interestingly, in some rare processes, such as BR($B_s \to \mu^+ \mu^-$ ), we find that contributions arising from CP-violating phases can bring the potentially large SUSY contributions into better agreement with experiment and Standard Model predictions., Comment: Version to appear in PRD

This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.

The primary goal of any future hadron collider is to discover new physics (NP) associated with a high mass scale, $M$, beyond the range of the LHC. In order to maintain the same {\it relative} mass reach for NP, $M/{\sqrt s}$, as $\sqrt s$ increases, Richter recently reminded us that the required integrated luminosity obtainable at future hadron colliders (FHC) must grow rapidly, $\sim s$, in the limit of naive scaling. This would imply, eg, a $\sim 50$-fold increase in the required integrated luminosity when going from the 14 TeV LHC to a FHC with $\sqrt s=100$ TeV, an increase that would prove quite challenging on many different fronts. In this paper we point out, due to the scaling violations associated with the evolution of the parton density functions (PDFs) and the running of the strong coupling, $\alpha_s$, that the actual luminosity necessary in order to maintain any fixed value of the relative mass reach is somewhat greater than this scaling result indicates. However, the actual values of the required luminosity scaling are found to be dependent upon the detailed nature of the NP being considered. Here we elucidate this point explicitly by employing several specific benchmark examples of possible NP scenarios and briefly discuss the (relatively weak) search impact in each case if these luminosity goals are not met., Comment: 17 pages, 7 figs, latex; updated discussion etc, new figs and table added

The production of new gauge bosons is a standard benchmark for the exploration of the physics capabilities of future colliders. The $\sqrt s=100$ TeV Future Hadron Collider will make a major step in our ability to search for and explore the properties of such new states. In this paper, employing traditional models to make contact with the past and more recent literature, we not only establish in detail the discovery and exclusion reaches for both the $Z'$ and $W'$ within these models but, more importantly, we also examine the capability of the FHC to extract information relevant for the determination of the couplings of the $Z'$ to the fermions of the Standard Model as well as the helicity of the corresponding $W'$ couplings. This is a necessary first step in determining the nature of the underlying theory which gave rise to these states., Comment: 34 pages, 19 figs; Figures, discussion and references added

The search for and potential identification of dark matter (DM) will require a simultaneous, multi-pronged approach with important roles to be played by the LHC, both direct and indirect DM detection experiments and, eventually, the ILC. The 19-parameter p(henomenological)MSSM can provide a broad framework for complementarity studies of neutralino DM. In this talk, I summarized the sensitivity of these searches at the 7, 8 and 14 TeV LHC, combined with those from \Fermi, CTA, IceCube/DeepCore, COUPP, LZ and XENON. The strengths and weaknesses of each of these searches is briefly discussed as is their interdependent roles in probing the pMSSM model parameter space. I also comment on the future role of the ILC in exploring the detailed nature of neutralino DM., Comment: 16 pages, 8 figs. Talk presented at the International Workshop on Future Linear Colliders(LCWS13), Tokyo, Japan, 11-15 November 2013

In this Snowmass whitepaper, we describe the impact of ongoing and proposed intensity frontier experiments on the parameter space of the Minimally Supersymmetric Standard Model (MSSM). We extend a set of phenomenological MSSM (pMSSM) models to include non-zero CP-violating phases and study the sensitivity of various flavor observables in these scenarios Future electric dipole moment and rare meson decay experiments can have a strong impact on the viability of these models that is relatively independent of the detailed superpartner spectrum. In particular, we find that these experiments have the potential to probe models that are expected to escape searches at the high-luminosity LHC., Comment: 10 pages, 2 figures. Contributed to the Community Summer Study 2013, Minneapolis, MN July 29 - August 6, 2013

We present several benchmark points in the phenomenological Minimal Supersymmetric Standard Model (pMSSM). We select these models as experimentally well-motivated examples of the MSSM which predict the observed Higgs mass and dark matter relic density while evading the current LHC searches. We also use benchmarks to generate spokes in parameter space by scaling the mass parameters in a manner which keeps the Higgs mass and relic density approximately constant., Comment: 10 pages, 6 figures

We further examine the capability of the 7 and 8 TeV LHC to explore the parameter space of the p(henomenological)MSSM with neutralino LSPs. Here we present an updated study employing all of the relevant ATLAS SUSY analyses, as well as all relevant LHC non-MET searches, whose data were publically available as of mid-September 2012. We find that roughly 1/3 of our pMSSM model points are excluded at present with an important role being played by both the heavy flavor and multi-lepton searches, as well as those for heavy stable charged particles. Nonetheless, we find that light gluinos, 1st/2nd generation squarks, and stop/sbottoms (\lsim 400-700 GeV), as well as models with 1% fine-tuning or better, are still viable in the pMSSM. In addition, we see that increased luminosity at 8 TeV is unlikely to significantly improve the reach of the "vanilla" searches. The impact of these null searches on the SUSY sparticle spectrum is discussed in detail and the implications of these results for models with low fine-tuning, a future lepton collider and dark matter searches are examined., Comment: 33 pages, 9 figures

The mixing of the imaginary parts of the transition amplitudes of nearby resonances via the breakdown of the Breit-Wigner approximation has been shown to lead to potentially large modifications in the signal rates for new physics at colliders. In the case of suppression, this effect may be significant enough to lead to some new physics signatures being initially missed in searches at, e.g., the LHC. Here we explore the influence of this `width mixing' on the production of the nearly degenerate, level-2 Kaluza-Klein (KK) neutral gauge bosons present in Split-UED. We demonstrate that in this particular case large cross section modifications in the resonance region are necessarily absent and explain why this is so based on the group theoretical structure of the SM., Comment: 10 pages, 2 figures; discussion and references added

The recent discovery of a 125 GeV Higgs, as well as the lack of any positive findings in searches for supersymmetry, has renewed interest in both the supersymmetric Higgs sector and fine-tuning. Here, we continue our study of the phenomenological MSSM (pMSSM), discussing the light Higgs and fine-tuning within the context of two sets of previously generated pMSSM models. We find an abundance of models with experimentally-favored Higgs masses and couplings. We investigate the decay modes of the light Higgs in these models, finding strong correlations between many final states. We then examine the degree of fine-tuning, considering contributions from each of the pMSSM parameters at up to next-to-leading-log order. In particular, we examine the fine-tuning implications for our model sets that arise from the discovery of a 125 GeV Higgs. Finally, we investigate a small subset of models with low fine-tuning and a light Higgs near 125 GeV, describing the common features of such models. We generically find a light stop and bottom with complex decay patterns into a set of light electroweak gauginos, which will make their discovery more challenging and may require novel search techniques., Comment: 52 pages, 31 figures; minor changes, typos fixed, references added

The pMSSM provides a broad perspective on SUSY phenomenology. In this paper we generate two new, very large, sets of pMSSM models with sparticle masses extending up to 4 TeV, where the lightest supersymmetric particle (LSP) is either a neutralino or gravitino. The existence of a gravitino LSP necessitates a detailed study of its cosmological effects and we find that Big Bang Nucleosynthesis places strong constraints on this scenario. Both sets are subjected to a global set of theoretical, observational and experimental constraints resulting in a sample of \sim 225k viable models for each LSP type. The characteristics of these two model sets are briefly compared. We confront the neutralino LSP model set with searches for SUSY at the 7 TeV LHC using both the missing (MET) and non-missing ET ATLAS analyses. In the MET case, we employ Monte Carlo estimates of the ratios of the SM backgrounds at 7 and 8 TeV to rescale the 7 TeV data-driven ATLAS backgrounds to 8 TeV. This allows us to determine the pMSSM parameter space coverage for this collision energy. We find that an integrated luminosity of \sim 5-20 fb^{-1} at 8 TeV would yield a substantial increase in this coverage compared to that at 7 TeV and can probe roughly half of the model set. If the pMSSM is not discovered during the 8 TeV run, then our model set will be essentially void of gluinos and lightest first and second generation squarks that are \lesssim 700-800 GeV, which is much less than the analogous mSUGRA bound. Finally, we demonstrate that non-MET SUSY searches continue to play an important role in exploring the pMSSM parameter space. These two pMSSM model sets can be used as the basis for investigations for years to come., Comment: 54 pages, 22 figures; typos fixed, references added

The $E_6$SSM extension of the MSSM allows for the solution of many of the difficulties that are usually encountered within conventional SUSY breaking scenarios, e.g., the $\mu$ problem, the imposition of R-parity 'by hand', the generation of light neutrino masses and obtaining a light Higgs boson with a mass as large as $\sim$ 125 GeV as suggested by recent LHC measurements. In addressing these problems, such a scenario predicts the existence of additional singlet and vector-like superfields beyond those in the MSSM as well as possibly two new neutral gauge bosons near the TeV scale. In this paper the phenomenological implications of simultaneous gauge kinetic mixing between the usual Standard Model (SM) hypercharge gauge field and both these new neutral gauge fields present in the $E_6$SSM scenario is explored. To this end a large class of specific toy models realizing this type of kinetic mixing is examined. In particular, we demonstrate that a significant suppression (or enhancement) of the expected event rate for $Z'$ production in the dilepton channel at the LHC is not likely to occur in this scenario due to gauge kinetic mixing., Comment: 17 pages, 3 figs; text and references updated

Radiation amplitude zeros have long been used to test the Standard Model. Here, we consider the supersymmetric radiation amplitude zero in chargino-neutralino associated production, which can be observed at the luminosity upgraded LHC. Such an amplitude zero only occurs if the neutralino has a large wino fraction and hence this observable can be used to determine the neutralino eigenstate content. We find that this observable can be measured by comparing the p_T spectrum of the softest lepton in the trilepton $\chi_1^\pm \chi_2^0$ decay channel to that of a control process such as $\chi_1^+ \chi_1^-$ or $\chi_2^0 \chi_2^0$. We test this technique on a previously generated model sample of the 19 dimensional parameter space of the phenomenological MSSM, and find that it is effective in determining the wino content of the neutralino., Comment: 19 pages, 7 figures

The OPERA collaboration has reported the observation of superluminal muon neutrinos, whose speed $v_\nu$ exceeds that of light $c$, with $(v_\nu - c)/c \simeq 2.5 \times 10^{-5}$. In a recent work, Cohen and Glashow (CG) have refuted this claim by noting that such neutrinos will lose energy, by pair-emission of particles, at unacceptable rates. Following the CG arguments, we point out that pair-emissions consistent with the OPERA anomaly can lead to detectable signals from decays of highly boosted top quarks at the LHC, allowing an independent test of the superluminal neutrino hypothesis., Comment: 7 pages, 2 figures, Latex. New material, including figures and references, added. Conclusions unchanged

We investigate the model independent nature of the Supersymmetry search strategies at the 7 TeV LHC. To this end, we study the missing-transverse-energy-based searches developed by the ATLAS Collaboration that were essentially designed for mSUGRA. We simulate the signals for ~71k models in the 19-dimensional parameter space of the pMSSM. These models have been found to satisfy existing experimental and theoretical constraints and provide insight into general features of the MSSM without reference to a particular SUSY breaking scenario or any other assumptions at the GUT scale. Using backgrounds generated by ATLAS, we find that imprecise knowledge of these estimated backgrounds is a limiting factor in the potential discovery of these models and that some channels become systematics-limited at larger luminosities. As this systematic error is varied between 20-100%, roughly half to 90% of this model sample is observable with significance S>5 for 1 fb^{-1} of integrated luminosity. We then examine the model characteristics for the cases which cannot be discovered and find several contributing factors. We find that a blanket statement that squarks and gluinos are excluded with masses below a specific value cannot be made. We next explore possible modifications to the kinematic cuts in these analyses that may improve the pMSSM model coverage. Lastly, we examine the implications of a null search at the 7 TeV LHC in terms of the degree of fine-tuning that would be present in this model set and for sparticle production at the 500 GeV and 1 TeV Linear Collider., Comment: 51 pages, 26 figures

We examine the implications of the recent CDF measurement of the top-quark forward-backward asymmetry, focusing on a scenario with a new color octet vector boson at 1-3 TeV. We study several models, as well as a general effective field theory, and determine the parameter space which provides the best simultaneous fit to the CDF asymmetry, the Tevatron top pair production cross section, and the exclusion regions from LHC dijet resonance and contact interaction searches. Flavor constraints on these models are more subtle and less severe than the literature indicates. We find a large region of allowed parameter space at high axigluon mass and a smaller region at low mass; we match the latter to an SU(3)xSU(3)/SU(3) coset model with a heavy vector-like fermion. Our scenario produces discoverable effects at the LHC with only 1-2 inverse femtobarns of luminosity at 7-8 TeV. Lastly, we point out that a Tevatron measurement of the b-quark forward-backward asymmetry would be very helpful in characterizing the physics underlying the top-quark asymmetry., Comment: 35 pages, 10 figures, 4 tables

In $e^+e^-$ collisions, transverse beam polarization can be a useful tool in studying the properties of particles associated with new physics beyond the Standard Model(SM). However, unlike in the case of measurements associated with longitudinal polarization, the formation of azimuthal asymmetries used to probe this physics in the case of transverse polarization requires both $e^\pm$ beams to be simultaneously polarized. In this paper we discuss the further use of transverse polarization as a probe of new physics models at a high energy, $\sqrt s=3$ TeV version of CLIC. In particular, we show ($i$) how measurements of the sign of these asymmetries is sufficient to discriminate the production of spin-0 supersymmetric states from the spin-1/2 Kaluza-Klein excitations of Universal Extra Dimensions. Simultaneously, the contribution to this asymmetry arising from the potentially large SM $W^+W^-$ background can be made negligibly small. We then show ($ii$) how measurements of such asymmetries and their associated angular distributions on the peak of a new resonant $Z'$-like state can be used to extract precision information on the $Z'$ couplings to the SM fermions., Comment: 16 pages, 8 figures. Based on a talk given at the International Workshop on Linear Colliders, CERN, Geneva, Switzerland, 18-22 Oct 2010; typos corrected

The discovery and exploration of Supersymmetry in a model-independent fashion will be a daunting task due to the large number of soft-breaking parameters in the MSSM. In this paper, we explore the capability of the ATLAS detector at the LHC ($\sqrt s=14$ TeV, 1 fb$^{-1}$) to find SUSY within the 19-dimensional pMSSM subspace of the MSSM using their standard transverse missing energy and long-lived particle searches that were essentially designed for mSUGRA. To this end, we employ a set of $\sim 71$k previously generated model points in the 19-dimensional parameter space that satisfy all of the existing experimental and theoretical constraints. Employing ATLAS-generated SM backgrounds and following their approach in each of 11 missing energy analyses as closely as possible, we explore all of these $71$k model points for a possible SUSY signal. To test our analysis procedure, we first verify that we faithfully reproduce the published ATLAS results for the signal distributions for their benchmark mSUGRA model points. We then show that, requiring all sparticle masses to lie below 1(3) TeV, almost all(two-thirds) of the pMSSM model points are discovered with a significance $S>5$ in at least one of these 11 analyses assuming a 50\% systematic error on the SM background. If this systematic error can be reduced to only 20\% then this parameter space coverage is increased. These results are indicative that the ATLAS SUSY search strategy is robust under a broad class of Supersymmetric models. We then explore in detail the properties of the kinematically accessible model points which remain unobservable by these search analyses in order to ascertain problematic cases which may arise in general SUSY searches., Comment: 69 pages, 40 figures, Discussion added