Search

A weighted average weak mixing angle θW derived from relatively low Q² experiments is compared with the standard model prediction obtained from precision measurements. The approximate 1.8 sigma discrepancy is fit with an intermediate mass (~10-35 GeV) "dark" Z boson Zd, corresponding to a U(l)d gauge symmetry of hidden dark matter, which couples to our world via kinetic and Z-Zd mass mixing. Constraints on such a scenario are obtained from precision electroweak bounds and searches for the rare Higgs decays H → ZZd → 4 charged leptons at the LHC. The sensitivity of future anticipated low Q² measurements of sin² θW (Q²) to intermediate mass Zd is also illustrated. This dark Z scenario can provide interesting concomitant signals in low energy parity violating measurements and rare Higgs decays at the LHC over the next few years. [ABSTRACT FROM AUTHOR]

The insular nature of the Standard Model may be explained if the Higgs mass parameter is only sensitive to quantum corrections from physical states. Starting from a scale-free electroweak sector at tree level, we postulate that quantum effects of heavy right-handed neutrinos induce a mass term for a scalar weak doublet that contains the dark matter particle. In turn, below the scale of heavy neutrinos, the dark matter sector sets the scale of the Higgs potential. We show that this framework can lead to a Higgs mass that respects physical naturalness, while also providing a viable scalar dark matter candidate, realistic light neutrino masses, and the baryon asymmetry of the Universe via thermal leptogenesis. The proposed scenario can remain perturbative and stable up to the Planck scale, thereby accommodating simple extensions to include a high-scale (~2×1016 GeV) inflationary sector, implied by recent measurements. In that case, our model typically predicts that the dark matter scalar is close to 1 TeV in mass and could be accessible in near future direct detection experiments. [ABSTRACT FROM AUTHOR]

In two-Higgs doublet extensions of the Standard Model, flavor-changing neutral current constraints can be addressed by introducing a U(1)' gauge symmetry, under which the Higgs doublets carry different charges. That scenario implies the presence of a H±W±Z' vertex at tree level. For the light "dark" Z model (Z' = Zd) with mZj < 10 GeV, such a coupling leads to the dominant decay mode H± W± + Zd (for mH± ≾ 175 GeV), rather than the usual type I model decay HH± → τ± ν, for a broad range of parameters. We find that current analyses do not place significant bounds on this scenario. Over much of the parameter space considered, the decay of a pair-produced t (t) into H+ b (H-b) provides the dominant H± production. Analysis of available LHC data can likely cover significant ranges of our parameters, if Zd → µ+µ- has a branching ratio of ~20%. If the Zd decays mainly invisibly then probing the entire relevant parameter space would likely require additional data from future LHC runs. We briefly discuss the phenomenology for mH± g 175 GeV. [ABSTRACT FROM AUTHOR]

The "gravitational baryogenesis" scenario is extended to generate both baryon and dark matter asymmetries in the matter dominated era corresponding to post-inflationary reheating. A minimal extension requires a singlet fermion X for dark matter and a singlet scalar S. With two or more hidden sector fermions, the scenario can lead to nucleón decay into dark matter with a lifetime of order 1034-36 yr, which is relevant for current or future experiments. The correct multicomponent relic density can be obtained if dark matter fermions couple to a sub-GeV vector boson that weakly interacts with the standard model through mixing. The typical inflationary scale in the scenario is of order 1016 GeV which suggests that tensor mode perturbations could potentially be within observational reach. [ABSTRACT FROM AUTHOR]

We show that weak scale vectorlike fermions with order one couplings to the Higgs can lead to a novel mechanism for a strongly first-order electroweak phase transition through their tendency to drive the Higgs quartic coupling negative. These same fermions could also enhance the loop-induced branching fraction of the Higgs into two photons, as suggested by the recent discovery of a ~ 125 GeV Higgs-like state at the CERN LHC. Our results suggest that measurements of the diphoton decay rate of the Higgs and its self-coupling, at the LHC or perhaps at a future lepton collider, could probe the electroweak phase transition in the early Universe, with significant implications for the viability of electroweak baryogenesis scenarios. [ABSTRACT FROM AUTHOR]

We propose that the LHC hints for a Higgs diphoton excess and the muon g -- 2 (gµ - 2) discrepancy between theory and experiment may be related by vectorlike "leptons" charged under both U(1)Y hypercharge and a "dark" U(1)d. Quantum loops of such leptons can enhance the Higgs diphoton rate and also generically lead to U(1)y-U(1)d kinetic mixing. The induced coupling of a light U(1)d gauge boson Zd to electric charge can naturally explain the measured gµ - 2. We update Zd mass and coupling constraints based on comparison of the electron g -- 2 experiment and theory, and find that explaining gµ-2 while satisfying other constraints requires Zd to have a mass ∼20-100 MeV. We predict new Higgs decay channels γZd and ZdZd, with rates below the diphoton mode but potentially observable. The boosted Zd → e+e- in these decays would mimic a promptly converted photon and could provide a fraction of the apparent diphoton excess. More statistics or a closer inspection of extant data may reveal such events. [ABSTRACT FROM AUTHOR]

Precision data generally require the threshold for physics beyond the Standard Model to be at the deca-TeV (10 TeV) scale or higher. This raises the question of whether there are interesting deca-TeV models for which the LHC may find direct clues. A possible scenario for such physics is a 5D warped model of fermion masses and mixing, with Kaluza-Klein masses mKK ~10 TeV, allowing it to avoid tension with stringent constraints, especially from flavor data. Discovery of a Standard-Model-like Higgs boson, for which there are some hints at ~125 GeV at the LHC, would also require the Kaluza-Klein masses to be at or above 10 TeV. These warped models generically predict the appearance of a much lighter radion scalar. We find that, in viable warped models of flavor, a radion with a mass of a few hundred GeV and an inverse coupling of order mKK ~10 TeV could typically be accessible to the LHC experiments--with √S=14 TeV and ~100 fb-1 of data. The above statements can be applied, mutatis mutandis, to 4D dual models, where conformai dynamics and a dilaton replace warping and the radion, respectively. Detection of such a light and narrow scalar could thus herald the proximity of a new physical threshold and motivate experiments that would directly probe the deca-TeV mass scale. [ABSTRACT FROM AUTHOR]

If fermion condensation is a main source of electroweak symmetry breaking, an ultra-heavy Higgs doublet of mass ∼ 108 GeV can yield naturally small Dirac neutrino masses. We show that such a scenario can lead to a new leptogenesis mechanism based on the decays of the ultra-heavy Higgs. Given its very large mass, the requisite Higgs doublet can be considered an elementary particle and would point to a cutoff scale ∼1010 GeV. We outline how our scenario can also naturally lead to composite asymmetric dark matter. Some potential signals of this scenario are discussed. [ABSTRACT FROM AUTHOR]

General consequences of mass mixing between the ordinary Ζ boson and a relatively light Z,d boson, the "dark" Z, arising from a U(1)d gauge symmetry, associated with a hidden sector such as dark matter, are examined. New effects beyond kinetic mixing are emphasized. Z-Zd mixing introduces a new source of low energy parity violation well explored by possible future atomic parity violation and planned polarized electron scattering experiments. Rare K(B) meson decays into π(Κ)ℓ+ℓ-(ℓ = e, μ) and π(K)vv̄ are found to already place tight constraints on the size of Z-Zd mixing. Those sensitivities can be further improved with future dedicated searches at Κ and Β factories as well as binned studies of existing data. Z-Zd mixing can also lead to the Higgs decay Η → ZZd, followed by Ζ → ℓ+1ℓ-1 and Zd → ℓ+2ℓ-2 or "missing energy," providing a potential hidden sector discovery channel at the Large Hadron Collider. An illustrative realization of these effects in a 2 Higgs doublet model is presented. [ABSTRACT FROM AUTHOR]

We examine loop-mediated effects of new heavy quarks Q = (t′, b′) on t&tmacr; production at hadron colliders, using a phenomenological model with flavor off-diagonal couplings of charged and neutral scalars &phis; = (&phis;±, &phis;0) to Q. We show that an invariant-mass-dependent asymmetry, in the t&tmacr; center of mass, consistent with those recently reported by the CDF collaboration, can be obtained for quark masses around 350-500 GeV, scalar masses of order 100-200 GeV, and modest-to-strong Yukawa couplings. The requisite strong interactions suggest a nonperturbative electroweak-symmetry-breaking mechanism and composite states at the weak scale. A typical prediction of this framework is that the new heavy quarks decay dominantly into t&phis; final states [ABSTRACT FROM AUTHOR]

We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause induced nucleon decay by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of 1029-1032 yrs in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter-induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations. [ABSTRACT FROM AUTHOR]

Recent results from the MINOS accelerator neutrino experiment suggest a possible difference between νμ and ν¯μ disappearance oscillation parameters, which one may ascribe to a new long-distance potential acting on neutrinos. As a specific example, we consider a model with gauged B - Le - 2Lτ number that contains an extremely light new vector boson mZ′ < 10-18 eV and extraordinarily weak coupling α′ ≲ 10-52 (or larger mZ′ if cosmology bounds on neutrino decay apply). In that case, differences between νμ → ντ and ν¯μ → ν¯τ oscillations can result from a long-range potential due to neutrons in the Earth and the Sun that distinguishes νμ and ντ on Earth, with a potential difference of ∼6 × 10-14 eV, and changes sign for antineutrinos. We show that existing solar, reactor, accelerator, and atmospheric neutrino oscillation constraints can be largely accommodated for values of parameters that help explain the possible MINOS anomaly by this new physics, although there is some tension with atmospheric constraints. A long-range interaction, consistent with current bounds, could have very pronounced effects on atmospheric neutrino disappearance in the 15-40 GeV range that will be studied with the IceCube DeepCore array, currently in operation, and can have a significant effect on future high-precision long-baseline oscillation experiments that aim for ±1% sensitivity, in νμ and ν¯μ disappearance, separately. Together, these experiments can extend the reach for new long-distance effects well beyond current bounds and test their relevance to the aforementioned MINOS anomaly. We also point out that long-range potentials originating from the Sun could lead to annual modulations of neutrino data at the percent level, due to the variation of the Earth-Sun distance. A similar phenomenology is shown to apply to other potential new gauge symmetries such as L - 3Lτ and B - 3Lτ. [ABSTRACT FROM AUTHOR]

The Randall-Sundrum (RS) model, based on a slice of warped 5D spacetime, was originally introduced to explain the apparent hierarchy between the scales of weak and gravitational interactions. Over the past decade, this model has been extended to provide a predictive theory of flavor, as well as to address various constraints from precision data. In this talk, we will present a brief review of the RS model and some of its extensions. A survey of some key signatures of realistic warped models and the experimental challenges they pose will be presented. We will also consider truncated warped scenarios that address smaller hierarchies and discuss why their discovery can have improved prospects, at the LHC. [Copyright &y& Elsevier]

Pseudoscalar particles, often referred to as axionlike-particles (ALPs), arise in a variety of theoretical contexts. The phenomenology of such states is typically studied while assuming flavor-conserving interactions, yet they can in principle have flavor-violating (FV) couplings to fermions. We consider this general possibility while focusing on models where the ALP has non-negligible coupling to the Standard Model Higgs boson h. For a lepton FV ALP a of mass ma≳2 GeV, a→τℓ, where ℓ≠τ is a charged lepton, could have an Ϭ(1) branching fraction, leading to a potentially detectable h→aa→τℓτℓ at the LHC and its future program. We examine this possibility, in light of existing bounds on FV processes, in a general effective theory. We obtain constraints on the effective couplings from both prompt and long-lifetime searches at the LHC; some projections for envisioned measurements are also provided. The implications of the recently announced first results of the muon g-2 measurement at Fermilab for the ALP interactions considered in our work are also briefly discussed. [ABSTRACT FROM AUTHOR]

A modest extension of the Standard Model by two additional Higgs doublets--the Higgs troika model--can provide a well-motivated scenario for successful baryogenesis if neutrinos are Dirac fermions. Adapting the "spontaneous flavor violation" framework, we consider a version of the troika model where light quarks have significant couplings to the new multi-TeV Higgs states. Resonant production of new scalars leading to dijet or top-pair signals are typical predictions of this setup. The initial- and final-state quarks relevant to the collider phenomenology also play a key role in baryogenesis, potentially providing direct access to the relevant early-Universe physics in high-energy experiments. Viable baryogenesis generally prefers some hierarchy of masses between the observed and the postulated Higgs states. We show that there is a complementarity between direct searches at a future 100 TeV pp collider and indirect searches at flavor experiments, with both sensitive to different regions of parameter space relevant for baryogenesis. In particular, measurements of D-̅D mixing at LHCb probe much of the interesting parameter space. Direct and indirect searches can uncover the new Higgs states up to masses of O(10) TeV, thereby providing an impressive reach to investigate this model. [ABSTRACT FROM AUTHOR]

Direct detection of light dark matter (DM), below the GeV scale, through electron recoil can be efficient if DM has a velocity well above the virial value of v~10-3. We point out that if there is a long range attractive force sourced by bulk ordinary matter, i.e., baryons or electrons, DM can be accelerated towards the Earth and reach velocities v~0.1 near the Earth's surface. In this "attractive scenario," all DM will be boosted to high velocities by the time it reaches direct detection apparatuses in laboratories. Furthermore, the attractive force leads to an enhanced DM number density at the Earth, facilitating DM detection even more. We elucidate the implications of this scenario for electron recoil direct detection experiments and find parameters that could lead to potential signals, while being consistent with stellar cooling and other bounds. Our scenario can potentially explain the recent excess in electron recoil signals reported by the XENON1T experiment in the ~keV energy regime as well as the hint for nonstandard stellar cooling. [ABSTRACT FROM AUTHOR]

The OPERA Collaboration has reported the observation of superluminal muon neutrinos, whose speed uv exceeds that of light c, with (uv - c)/c ≃ 2.5 x 10-5. In a recent work, Cohen and Glashow have refuted this claim by noting that such neutrinos will lose energy, by pair emission of particles, at unacceptable rates. Following the Cohen and Glashow arguments, we point out that pair emissions consistent with the OPERA anomaly can lead to detectable signals for neutrinos originating from decays of highly boosted top quarks at the LHC, allowing an independent test of the superluminal neutrino hypothesis. [ABSTRACT FROM AUTHOR]

We describe a scenario where the smallness of neutrino masses is related to a global symmetry that is only violated by quantum gravitational effects. The coupling of neutrinos to gauge singlet right-handed fermions is attributed to symmetry preserving gravitational operators suppressed by the Planck mass, in this framework. The proposed scenario leads to axion particles that decay into neutrinos, which could be probed through cosmological measurements and may help explain the Hubble parameter tension. Depending on the details of the implementation, the scenario could provide axion dark matter candidates. [ABSTRACT FROM AUTHOR]

To explain the baryon asymmetry of the Universe, we extend the Standard Model (SM) with two additional Higgs doublets with small vacuum expectation values. The additional Higgs fields interact with SM fermions through complex Yukawa couplings, leading to new sources of C P violation. We propose a simple flavor model with O (1) or smaller Yukawa couplings for quarks and charged leptons, consistent with current flavor constraints. To generate neutrino masses and the baryon asymmetry, right-handed neutrinos in the ∼ 0.1 - 10     TeV range couple to the "Higgs troika." The new Higgs doublet masses are at or above the TeV scale, allowing for asymmetric decays into SM lepton doublets and right-handed neutrinos. The asymmetry in lepton doublets is then processed into a baryon asymmetry, similar to leptogenesis. Since the masses of the new fields could be near the TeV scale, there is potentially a rich high energy collider phenomenology, including observable deviations in the 125 GeV Higgs decay into muons and taus, as well as detectable low energy signals such as the electron electric dipole moment or μ → e γ. Hence, this is in principle a testable model for the generation of baryon asymmetry. [ABSTRACT FROM AUTHOR]

If dark matter (DM) originates from physics near the Planck scale it could be directly detected via its multiple scattering signals, yet this requires a large cross section for DM interactions with atoms. Hence, detection of such DM could imply mediation by new low mass messengers. We propose that a dark U(1)d remnant of the underlying spacetime geometry or a unified theory may survive down to small mass scales ∼1  GeV, connecting low energy standard model (SM) and Planck scale phenomena. Typical required cross sections for direct detection of Planck scale DM can be achieved through the U(1)d interactions of DM with SM quarks. Low energy intense sources may uncover the GeV scale messengers of Planckian physics, allowing for testable predictions. We assume that U(1)d is gauged baryon number, which implies several new electroweak charged particles are expected to arise near the weak scale to cancel gauge anomalies. The model generically gives rise to kinetic mixing between the U(1)d gauge boson and the photon, which may be measurable. In this scenario, direct detection of DM and measurements of a low energy messenger, including its kinetic mixing with the photon, can potentially shed light on the high energy character of the scenario. Astrophysical considerations related to white dwarf stability against runaway nuclear fusion potentially disfavor DM heavier than ~1017 GeV within our assumed messenger model. [ABSTRACT FROM AUTHOR]

We propose that neutrino masses can be zero in vacuo and may be generated by the local distribution of dark matter through a feeble long range scalar force. We discuss potential phenomenological constraints and implications of this framework. Our model typically implies that the cosmic neutrino background left over from the big bang is mostly absent in our Galactic neighborhood. Hence, a positive detection signal from future proposed experiments, such as PTOLEMY, could in principle falsify our scenario. [ABSTRACT FROM AUTHOR]

We entertain the possibility that neutrino masses and dark matter (DM) originate from a common composite dark sector. A minimal effective theory can be constructed based on a dark SU(3)D interaction with three flavors of massless dark quarks; electroweak symmetry breaking gives masses to the dark quarks. By assigning a Z2 charge to one flavor, a stable "dark kaon" can provide a good thermal relic DM candidate. We find that "dark neutrons" may be identified as right handed Dirac neutrinos. Some level of "neutron-anti-neutron" oscillation in the dark sector can then result in non-zero Majorana masses for light standard model neutrinos. A simple ultraviolet completion is presented, involving additional heavy SU(3)D-charged particles with electroweak and lepton Yukawa couplings. At our benchmark point, there are "dark pions" that are much lighter than the Higgs and we expect spectacular collider signals arising from the UV framework. This includes the decay of the Higgs boson to ττℓℓ', where ℓ(ℓ') can be any lepton, with displaced vertices. We discuss the observational signatures of this UV framework in dark matter searches and primordial gravitational wave experiments; the latter signature is potentially correlated with the H→ττℓℓ' decay. [ABSTRACT FROM AUTHOR]

We consider a feeble repulsive interaction between ordinary matter and dark matter, with a range similar to or larger than the size of the Earth. Dark matter can thus be repelled from the Earth, leading to null results in direct detection experiments, regardless of the strength of the short-distance interactions of dark matter with atoms. Generically, such a repulsive force would not allow trapping of dark matter inside astronomical bodies. In this scenario, accelerator-based experiments may furnish the only robust signals of asymmetric dark matter models, which typically lack indirect signals from self-annihilation. Some of the variants of our hypothesis are also briefly discussed. [ABSTRACT FROM AUTHOR]

In warped 5D models of hierarchy and flavor, the first Kaluza-Klein (KK) state of the graviton G1 is heavy enough to decay into a photon and its first KK mode γ1 on-shell: G1 → γ1γ. The volume-suppression of the rate for this process [relative to 2-body decay into heavy Standard Model (SM) final states (W/Z/t/H)] may be partially compensated by the simplicity of the photon final state. We consider γ1 → W+W-, with a typical O(1) branching fraction, and focus on the semileptonic final state W(→ jj)W(→ ℓ,ν) with ℓ = e,μ. The SM background originates from 2 → 3 parton processes and is relatively suppressed compared to those for 2-body decays of G1. Moreover, to further reduce the background, we can impose an invariant mass window cut for γ1 (in addition to that for G1) in this new channel. We emphasize that this "photon cascade" decay probes a different combination of (bulk and brane) interactions of the KK states than the decays into two heavy SM states. Thus, in combination with other channels, the cascade decay could be used to extract the individual underlying geometric parameters. The 3σ reach for G1 in our channel is up to 1.5 TeV at the high luminosity (14 TeV) LHC, and can be extended to about 4 TeV, at 5σ, at a future 100 TeV hadron collider. Along the way, we point out the novel feature that the invariant mass distribution of KK graviton decay products becomes skewed from the Breit-Wigner form, due to the KK graviton coupling growing with energy. [ABSTRACT FROM AUTHOR]

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem – is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades. [Copyright &y& Elsevier]