Hiding a Heavy Higgs Boson at the 7 TeV LHC

A heavy Standard Model Higgs boson is not only disfavored by electroweak precision observables but is also excluded by direct searches at the 7 TeV LHC for a wide range of masses. Here, we examine scenarios where a heavy Higgs boson can be made consistent with both the indirect constraints and the direct null searches by adding only one new particle beyond the Standard Model. This new particle should be a weak multiplet in order to have additional contributions to the oblique parameters. If it is a color singlet, we find that a heavy Higgs with an intermediate mass of 200 - 300 GeV can decay into the new states, suppressing the branching ratios for the standard model modes, and thus hiding a heavy Higgs at the LHC. If the new particle is also charged under QCD, the Higgs production cross section from gluon fusion can be reduced significantly due to the new colored particle one-loop contribution. Current collider constraints on the new particles allow for viable parameter space to exist in order to hide a heavy Higgs boson. We categorize the general signatures of these new particles, identify favored regions of their parameter space and point out that discovering or excluding them at the LHC can provide important indirect information for a heavy Higgs. Finally, for a very heavy Higgs boson, beyond the search limit at the 7 TeV LHC, we discuss three additional scenarios where models would be consistent with electroweak precision tests: including an additional vector-like fermion mixing with the top quark, adding another U(1) gauge boson and modifying triple-gauge boson couplings.Comment: 42 pages, 12 figure

New Physics Models of Direct CP Violation in Charm Decays

In view of the recent LHCb measurement of Delta A_CP, the difference between the time-integrated CP asymmetries in D --> K+K- and D --> pi+pi- decays, we perform a comparative study of the possible impact of New Physics degrees of freedom on the direct CP asymmetries in singly Cabibbo suppressed D meson decays. We systematically discuss scenarios with a minimal set of new degrees of freedom that have renormalizable couplings to the SM particles and that are heavy enough such that their effects on the D meson decays can be described by local operators. We take into account both constraints from low energy flavor observables, in particular D0-D0bar mixing, and from direct searches. While models that explain the large measured value for Delta A_CP with chirally enhanced chromomagnetic penguins are least constrained, we identify a few viable models that contribute to the D meson decays at tree level or through loop induced QCD penguins. We emphasize that such models motivate direct searches at the LHC.Comment: 24 pages, 13 figures. v2: typos corrected, reference added, published versio

Spectrum-doubled heavy vector bosons at the LHC

We study a simple effective field theory incorporating six heavy vector bosons together with the standard-model field content. The new particles preserve custodial symmetry as well as an approximate left-right parity symmetry. The enhanced symmetry of the model allows it to satisfy precision electroweak constraints and bounds from Higgs physics in a regime where all the couplings are perturbative and where the amount of fine-tuning is comparable to that in the standard model itself. We find that the model could explain the recently observed excesses in di-boson processes at invariant mass close to 2 TeV from LHC Run 1 for a range of allowed parameter space. The masses of all the particles differ by no more than roughly 10%. In a portion of the allowed parameter space only one of the new particles has a production cross section large enough to be detectable with the energy and luminosity of Run 1, both via its decay to WZ and to Wh, while the others have suppressed production rates. The model can be tested at the higher-energy and higher-luminosity run of the LHC even for an overall scale of the new particles higher than 3 TeV

Warped Universal Extra Dimensions

We consider a 5D warped scenario with a KK-parity symmetry, where the non-trivial warping arises from the dynamics that stabilizes the size of the extra dimension. Generically, the lightest Kaluza-Klein (KK) particle is the first excitation of the radion field, while the next-to-lightest Kaluza-Klein particle is either the first excitation of the (RH) top quark or the first KK-parity odd Higgs. All these masses are expected to be of order the electroweak scale. We present simple analytical expressions for the masses and wavefunctions of the lowest lying KK modes, and derive the Feynman rules necessary for phenomenological applications. The framework allows to interpolate between a strongly warped scenario a la Randall-Sundrum (RS), and a weakly warped scenario that shares properties of both RS and Universal Extra Dimensions models.Comment: 41 pages, 13 figures. Minor comments added. Published versio

Simplified Models for LHC New Physics Searches

This document proposes a collection of simplified models relevant to the design of new-physics searches at the LHC and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the "Topologies for Early LHC Searches" workshop, held at SLAC in September of 2010, the purpose of which was to develop a set of representative models that can be used to cover all relevant phase space in experimental searches. Particular emphasis is placed on searches relevant for the first ~50-500 pb-1 of data and those motivated by supersymmetric models. This note largely summarizes material posted at http://lhcnewphysics.org/, which includes simplified model definitions, Monte Carlo material, and supporting contacts within the theory community. We also comment on future developments that may be useful as more data is gathered and analyzed by the experiments.Comment: 40 pages, 2 figures. This document is the official summary of results from "Topologies for Early LHC Searches" workshop (SLAC, September 2010). Supplementary material can be found at http://lhcnewphysics.or

Heavy Flavor Simplified Models at the LHC

We consider a comprehensive set of simplified models that contribute to final states with top and bottom quarks at the LHC. These simplified models are used to create minimal search strategies that ensure optimal coverage of new heavy flavor physics involving the pair production of color octets and triplets. We provide a set of benchmarks that are representative of model space, which can be used by experimentalists to perform their own optimization of search strategies. For data sets larger than 1/fb, same-sign dilepton and 3b search regions become very powerful. Expected sensitivities from existing and optimized searches are given.Comment: 33 pages, 17 figures, 5 table

Flavor Symmetric Sectors and Collider Physics

We discuss the phenomenology of effective field theories with new scalar or vector representations of the Standard Model quark flavor symmetry group, allowing for large flavor breaking involving the third generation. Such field content can have a relatively low mass scale \lesssim TeV and O(1) couplings to quarks, while being naturally consistent with both flavor violating and flavor diagonal constraints. These theories therefore have the potential for early discovery at LHC, and provide a flavor safe "tool box" for addressing anomalies at colliders and low energy experiments. We catalogue the possible flavor symmetric representations, and consider applications to the anomalous Tevatron t-tbar forward backward asymmetry and B_s mixing measurements, individually or concurrently. Collider signatures and constraints on flavor symmetric models are also studied more generally. In our examination of the t-tbar forward backward asymmetry we determine model independent acceptance corrections appropriate for comparing against CDF data that can be applied to any model seeking to explain the t-tbar forward backward asymmetry.Comment: 71 pages, 14 Figures, 12 Table

Status of low energy SUSY models confronted with the LHC 125 GeV Higgs data

Confronted with the LHC data of a Higgs boson around 125 GeV, different models of low energy SUSY show different behaviors: some are favored, some are marginally survived and some are strongly disfavored or excluded. In this note we update our previous scan over the parameter space of various low energy SUSY models by considering the latest experimental limits like the LHCb data for B_s->\mu^+\mu^- and the XENON 100(2012) data for dark matter-neucleon scattering. Then we confront the predicted properties of the SM-like Higgs boson in each model with the combined 7 TeV and 8 TeV Higgs search data of the LHC. For a SM-like Higgs boson around 125 GeV, we have the following observations: (i) The most favored model is the NMSSM, whose predictions about the Higgs boson can naturally (without any fine tuning) agree with the experimental data at 1-sigma level, better than the SM; (ii) The MSSM can fit the LHC data quite well but suffer from some extent of fine tuning; (iii) The nMSSM is excluded at 3-sigma level after considering all the available Higgs data; (iv) The CMSSM is quite disfavored since it is hard to give a 125 GeV Higgs boson mass and at the same time cannot enhance the di-photon signal rate.Comment: more comprehensive (table and figs showing chi-square added