Search

It has recently been proposed that dark matter could be a thermal relic of 3-to-2 scatterings in a strongly coupled hidden sector. We present explicit classes of strongly coupled gauge theories that admit this behavior. These are QCD-like theories of dynamical chiral symmetry breaking, where the pions play the role of dark matter. The number-changing 3-to-2 process, which sets the dark matter relic abundance, arises from the Wess-Zumino-Witten term. The theories give an explicit relationship between the 3-to-2 annihilation rate and the 2-to-2 self-scattering rate, which alters predictions for structure formation. This is a simple calculable realization of the strongly-interacting-massive-particle (SIMP) mechanism., Comment: 8 pages, 2 figures; v2: published in PRL under the title "Model for thermal relic dark matter of strongly interacting massive particles"

We present a simple model of weak-scale thermal dark matter that gives rise to X-ray lines. Dark matter consists of two nearly degenerate states near the weak scale, which are populated thermally in the early universe via co-annihilation with slightly heavier states that are charged under the Standard Model. The X-ray line arises from the decay of the heavier dark matter component into the lighter one via a radiative dipole transition, at a rate that is slow compared to the age of the universe. The model predicts observable signatures at the LHC in the form of exotic events with missing energy and displaced leptons and jets. As an application, we show how this model can explain the recently observed 3.55 keV X-ray line., Comment: 20 pages, 7 figures

We clarify several subtleties concerning the implementation of minimal flavor violation (MFV) in two Higgs doublet models. We derive all the exact and approximate predictions of MFV for the neutral scalar (h,H,A) Yukawa couplings to fermions. We point out several possible tests of this framework at the LHC., Comment: 13 pages

A new boson with mass ~125 GeV and properties similar to the Standard Model Higgs has been discovered by both the ATLAS and CMS collaborations, with significant observation in the ZZ* to 4 leptons and the diphoton channels. In this work we ask whether the signals in these two channels can be due primarily to two distinct resonances, each contributing dominantly to one channel. We investigate this question in the framework of a 2HDM and several of its extensions. We conservatively find that such a scenario is not possible in a pure 2HDM, nor under the addition of vector-like quarks, but is allowed when adding one or two top-like scalars, if one allows for sub-one tan\beta. The resonances in the diboson and diphoton channels can then be two scalars, or a scalar and a pseudoscalar, respectively. In each viable case, we further find the expected future deviations in the diboson, diphoton, b \bar b and tau tau rates, which will be useful in excluding the two-resonance scenario., Comment: 6 pages, 1 figure

Measurements of the Yukawa couplings of the recently discovered boson h to fermion pairs will provide a new arena for studying flavor physics. We analyze the lessons that can be learned by measuring the h decay rates into the charged lepton pairs, \tau\tau, \mu\mu, and \tau\mu. We demonstrate how this set of measurements can distinguish in principle between various classes of flavor models such as natural flavor conservation, minimal flavor violation, and Froggatt-Nielsen symmetry., Comment: 14 pages. v2: Minor corrections to Table 1 and Section 7; matches published version

We derive generic predictions at hadron colliders from the large forward-backward asymmetry observed at the Tevatron, assuming the latter arises from heavy new physics beyond the Standard Model. We use an effective field theory approach to characterize the associated unknown dynamics. By fitting the Tevatron t \bar t data we derive constraints on the form of the new physics. Furthermore, we show that heavy new physics explaining the Tevatron data generically enhances at high invariant masses both the top pair production cross section and the charge asymmetry at the LHC. This enhancement can be within the sensitivity of the 8 TeV run, such that the 2012 LHC data should be able to exclude a large class of models of heavy new physics or provide hints for its presence. The same new physics implies a contribution to the forward-backward asymmetry in bottom pair production at low invariant masses of order a permil at most., Comment: 11 pages, 6 figures. v2: added remarks on EFT validity range, dijet bounds and UV completions; matches published version

There is experimental evidence for a direct CP asymmetry in singly Cabibbo suppressed D decays, \Delta A_{CP} \sim 0.006. Naive expectations are that the Standard Model contribution to \Delta A_{CP} is an order of magnitude smaller. We explore the possibility that a major part of the symmetry comes from supersymmetric contributions. The leading candidates are models where the flavor structure of the trilinear scalar couplings is related to the structure of the Yukawa couplings via approximate flavor symmetries, particularly U(1), [U(1)]^2 and U(2). The recent hints for a lightest neutral Higgs boson with mass around 125 GeV support the requisite order one trilinear terms. The typical value of the supersymmetric contribution to the asymmetry is \Delta A_{CP}^{SUSY}\sim 0.001, but it could be accidentally enhanced by order one coefficients., Comment: 6 pages. v2: References added

The CDF and LHCb experiments have recently provided two intriguing hints for new physics: a large forward-backward asymmetry in $t\bar t$ production, and a direct CP asymmetry in D decays of order a percent. In both cases, flavor non-universal interactions are required in the up sector, raising the possibility that the two effects come from one and the same new physics source. We show that a minimal model, with an extra scalar doublet, previously suggested to explain the top data, gives -- without any modifications or additions -- a contribution to CP violation in charm decays that is of the right size., Comment: 4 pages. v3: A calculation of the contribution to epsilon^prime is presented; Conclusions unchanged

A large forward-backward asymmetry in $t\bar t$ production, for large invariant mass of the $t\bar t$ system, has been recently observed by the CDF collaboration. Among the scalar mediated mechanisms that can explain such a large asymmetry, only the t-channel exchange of a color-singlet weak-doublet scalar is consistent with both differential and integrated $t\bar t$ cross section measurements. Constraints from flavor changing processes dictate a very specific structure for the Yukawa couplings of such a new scalar. No sizable deviation in the differential or integrated $t\bar t$ production cross section is expected at the LHC., Comment: 22 pages, 1 figure and 2 tables. v2: Corrected Eqs.(50,51,74), adapted Fig.1, Tab.1 and relevant discussions. Extended discussion of top decay and single top

The CDF collaboration has recently reported a large deviation from the standard model of the t \bar t forward-backward asymmetry in the high invariant mass region. We interpret this measurement as coming from new physics at a heavy scale Lambda, and perform a model-independent analysis up to O(1/Lambda^4). A simple formalism to test and constrain models of new physics is provided. We find that a large asymmetry cannot be accommodated by heavy new physics that does not interfere with the standard model. We show that a smoking gun test for the heavy new physics hypothesis is a significant deviation from the standard model prediction for the t \bar t differential cross section at large invariant mass. At M_{t\bar t}>1 TeV the cross section is predicted to be at least twice that of the SM at the Tevatron, and for M_{t\bar t}>1.5 TeV at least three times larger than the SM at the LHC., Comment: 12 pages, 3 figures. v2: Minor corrections in the text, references added. v3: Extended discussion on QCD NLO corrections, added short discussion on LHC dijet constraints; matches published version

New physics at a high scale Lambda can affect top-related observables at O(1/Lambda^2) via the interference of effective four quark operators with the SM amplitude. The (\bar{u} gamma_mu gamma^5 T^a u)(\bar{t} gamma^mu gamma^5 T^a t) operator modifies the large M_{t\bar{t}} forward-backward asymmetry, and can account for the recent CDF measurement. The (\bar{u} gamma_mu T^a u)(\bar{t} gamma^mu T^a t) operator modifies the differential cross section, but cannot enhance the cross section of ultra-massive boosted jets by more than 60%. The hint for a larger enhancement from a recent CDF measurement may not persist future experimental improvements, or may be a QCD effect that is not accounted for by leading order and matched Monte Carlo tools or naive factorization. If it comes from new physics, it may stem from new light states or an O(1/Lambda^4) new physics effect., Comment: 7 pages, 2 figures and 2 tables. v2: References added. v3: Minor clarifications and modifications; matches published version

The D0 collaboration has recently announced evidence for a dimuon CP asymmetry in B_{d,s} decays of order one percent. If confirmed, this asymmetry requires new physics. We argue that for minimally flavor violating (MFV) new physics, and at low tan beta=v_u/v_d, there are only two four-quark operators (Q_{2,3}) that can provide the required CP violating effect. The scale of such new physics must lie below 260 GeV sqrt{tan beta}. The effect is universal in the B_s and B_d systems, leading to S_{psi K}~sin(2beta)-0.15 and S_{psi phi}~0.25. The effects on epsilon_K and on electric dipole moments are negligible. The most plausible mechanism is tree-level scalar exchange. MFV supersymmetry with low tan beta will be excluded. Finally, we explain how a pattern of deviations from the Standard Model predictions for S_{psi phi}, S_{psi K} and epsilon_K can be used to test MFV and, if MFV holds, to probe its structure in detail., Comment: 11 pages. v2: References added

Future high-precision flavor experiments may discover a pattern of deviations from the standard model predictions for flavor-changing neutral current processes. One of the interesting questions that can be answered then will be whether the flavor structure of the new physics is related to that of the standard model or not. We analyze this aspect of flavor physics within a specific framework: supersymmetric models where the soft breaking terms are dominated by gauge-mediation but get non-negligible contributions from gravity-mediation. We compare the possible patterns of non-minimally flavor-violating effects that arise if the gravity-mediated contributions are anarchical vs. the case that they are structured by a Froggatt-Nielsen symmetry. We show that combining information on flavor and CP violation from meson mixing and electric dipole moments is indicative for the flavor structure of gravity-mediation., Comment: 27 pages, 2 figures. v2: Introduction extended, reference added

A possible resolution of the flavor puzzle is that the fermion mass hierarchy can be dynamically generated through the coupling of the first two generation fields to a strongly coupled sector, which is approximately conformally invariant and leads to large anomalous dimensions for the first two generation fields over a large range of energies. We investigate the possibility of using the same sector to also break supersymmetry. We show that this automatically gives an "inverted hierarchy" in which the first two generation squarks and sleptons are much heavier than the other superpartners. Implementing this construction generically requires some fine-tuning in order to satisfy the constraints on flavor-changing neutral currents at the same time as solving the hierarchy problem. We show that this fine-tuning can be reduced to be milder than the percent level by making some technically natural assumptions about the form of the strongly coupled sector and its couplings to the standard model., Comment: 47 pages, 5 figures. v2: Added references and discussion on CP violation

We study the stability of the Higgs potential in the framework of the effective Lagrangian beyond the MSSM. While the leading nonrenormalizable operators can shift the Higgs boson mass above the experimental bound, they also tend to render the scalar potential unbounded from below. The destabilization is correlated with the Higgs mass increase, so that if quantum corrections are small the problem is severe. We show that a supersymmetric sub-leading correction stabilizes the potential within the domain of validity of the effective theory. Constraints on MSSM parameters as well as on higher dimensional operators are derived, ensuring that our vacuum has a lifetime longer than the present age of the universe. In addition we show that when effective operators are responsible for evading the LEP bound, stability constraints imply an upper bound on the scale of new physics in the few TeV range., Comment: 24 pages, 6 figures

We consider supersymmetric models where gauge mediation provides the dominant contributions to the soft supersymmetry breaking terms while gravity mediation provides sub-dominant yet non-negligible contributions. We further assume that the gravity-mediated contributions are subject to selection rules that follow from a Froggatt-Nielsen symmetry. This class of models constitutes an example of viable and natural non-minimally flavor violating models. The constraints from mixing in the neutral K system imply that the modifications to the Standard Model predictions for mixing in the neutral B_d and B_s systems are generically at most at the percent level, but can be of order ten percent for large $\tan \beta$. The modifications for the neutral D system mixing are generically at most of order a few percent, but in a special subclass of models they can be of order one. We point out $\Delta B=1$ processes relevant for flavor violation in hybrid mediation., Comment: 30 pages, 3 figures

In a class of AMSB models, the splitting in the Wino multiplet turns out to be very small, such as the often-quoted 170 MeV in minimal AMSB, which originates from MSSM loops. Such a small mass gap is potentially a window into higher scale physics, as it may be sensitive to higher-dimensional operators. We show that still within AMSB one can get a much larger splitting in the Wino multiplet--a few GeV--if the scale of the new physics is comparable to the gravitino mass (which is indeed often the scale of new physics in anomaly mediation)., Comment: 18 pages; v2: references added, matching journal version