Axion-mediated dark matter and Higgs diphoton signal
A bstractWe consider axion-mediated dark matter models motivated by Fermi gamma ray line at 130 GeV, where an axion-like scalar couples to a singlet Dirac fermion dark matter (DM) so its anomaly interactions with electroweak gauge bosons allow the DM to annihilate into monochromatic photon(s). In these models, extra vector-like leptons generate the necessary anomaly interactions for the axion and can also modify the Higgs-to-diphoton rate by their Yukawa couplings to the SM Higgs boson. We can distinguish models by the branching fraction of the DM annihilation into a photon pair, favoring the model with a triplet fermion. From the condition that the lighter charged extra lepton must be heavier than dark matter for no tree-level DM annihilations, we also show that the ratio of Higgs-to-diphoton rate to the SM value is constrained by vacuum stability to 1.4 (1.5) for the cutoff scale of 10 (1) TeV.

title: Interplay between Fermi gamma-ray lines and collider searches
abstract: A bstractWe explore the interplay between lines in the gamma-ray spectrum and LHC searches involving missing energy and photons. As an example, we consider a singlet Dirac fermion dark matter with the mediator for Fermi gamma-ray line at 130 GeV. A new chiral or local U(1) symmetry makes weak-scale dark matter natural and provides the axion or Z′ gauge boson as the mediator connecting between dark matter and electroweak gauge bosons. In these models, the mediator particle can be produced in association with a monophoton at colliders and it produces large missing energy through the decays into a DM pair or ZZ, Zγ with at least one Z decaying into a neutrino pair. We adopt the monophoton searches with large missing energy at the LHC and impose the bounds on the coupling and mass of the mediator field in the models. We show that the parameter space of the Z′ mediation model is already strongly constrained by the LHC 8TeV data, whereas a certain region of the parameter space away from the resonance in axion-like mediator models are bounded. We foresee the monophoton bounds on the Z′ and axion mediation models at the LHC 14 TeV.

title: The role of interference in unraveling the ZZ-couplings of the newly discovered boson at the LHC
abstract: We present a general procedure for measuring the tensor structure of the coupling of the scalar Higgs-like boson recently discovered at the LHC to two Z bosons, including the effects of interference among different operators. To motivate our concern with this interference, we explore the parameter space of the couplings in the effective theory describing these interactions and illustrate the effects of interference on the differential dilepton mass distributions. Kinematic discriminants for performing coupling measurements that utilize the effects of interference are developed and described. We present projections for the sensitivity of coupling measurements that use these discriminants in future LHC operation in a variety of physics scenarios.

title: Spin effects in the antler event topology at hadron colliders
abstract: A bstractWe investigate spin correlation effects in the “antler” event topology pp → A(A*) → B1B2 → (ℓ−C1)(ℓ+C2) at the LHC. We study the shapes of several kinematic variables, including the relative pseudorapidity, relative azimuthal angle and the energies of the two leptons, as well as several mass variables Mℓℓ, Meff, $ \sqrt {{{{s}_{{\min }}}}} $, MT2, MCT and MCTx. We focus on the two kinematic extremes of $\sqrt{S}$ — threshold and infinity — and derive analytical expressions for the differential distributions of several variables, most notably the cos $\theta_{{\ell -\ell +}}^{*}$ variable proposed by Barr in  For all possible spin assignments of particles A, B and C, we derive the cos $\theta_{{\ell -\ell +}}^{*}$ differential distribution at threshold, including the effects of spin correlations. Our analytical results help identify the problematic cases for spin discrimination.

title: Superpartner mass measurement technique using 1D orthogonal decompositions of the Cambridge transverse mass variable M(T2).
abstract: We propose a new model-independent technique for mass measurements in missing energy events at hadron colliders. We illustrate our method with the most challenging case of a single-step decay chain. We consider inclusive same-sign chargino pair production in supersymmetry, followed by leptonic decays to sneutrinos χ+ χ+ → ℓ+ ℓ'+ ν(ℓ)ν(ℓ') and invisible decays ν(ℓ) → ν(ℓ) χ(1)(0). We introduce two one-dimensional decompositions of the Cambridge MT2 variable: M(T2∥) and M(T2⊥), on the direction of the upstream transverse momentum P→T and the direction orthogonal to it, respectively. We show that the sneutrino mass Mc can be measured directly by minimizing the number of events N(Mc) in which MT2 exceeds a certain threshold, conveniently measured from the end point M(T2⊥)(max) (Mc).

title: From Lagrangians to Events: Computer Tutorial at the MC4BSM-2012 Workshop
abstract: This is a written account of the computer tutorial oered at the Sixth MC4BSM workshop at Cornell University, March 22-24, 2012. The tools covered during the tutorial include: FeynRules, LanHEP, MadGraph, CalcHEP, Pythia 8, Herwig++, and Sherpa. In the tutorial, we specify a simple extension of the Standard Model, at the level of a Lagrangian. The software tools are then used to automatically generate a set of Feynman rules, compute the invariant matrix element for a sample process, and generate both parton-level and fully hadronized/showered Monte Carlo event samples. The tutorial is designed to be self-paced, and detailed instructions for all steps are included in this write-up. Installation instructions for each tool on a variety of popular platforms are also provided.

title: Multi-lepton signals of multiple Higgs bosons
abstract: A bstractWe identify and investigate novel multi-lepton signatures of extended Higgs sectors at the LHC in the guise of CP- and flavor-conserving two-Higgs-doublet models (2HDMs). Rather than designing individual searches tailored to specific 2HDM signals, we employ the combination of many exclusive multi-lepton search channels to probe the collective signal from the totality of production and decay processes. Multi-lepton signals of 2HDMs can arise from a variety of sources, including Standard Model-like production of the CP-even scalars, h and H, through gluon-fusion with h, H → ZZ(∗), or associated production with vector bosons or top quarks, with h, H → WW(∗), ZZ(∗), ττ. Additional sources include gluon-fusion production of the heavy CP-even scalar with cascade decays through the light CP-even scalar, the CP-odd scalar, A, or the charged scalar, H±, such as H → hh, H → AA, H → H+H−, H → ZA, with A → Zh, ττ, H± → Wh, and h → WW∗, ZZ∗, ττ. Altogether, the combined multi-lepton signal may greatly exceed that of the Standard Model Higgs boson and provides a sensitive probe of extended Higgs sectors over a wide range of parameters. As a proof of principle, we use a factorized mapping procedure between model parameters and signatures to determine multi-lepton sensitivities in four different flavor conserving 2HDM parameter spaces by simulating the acceptance times efficiency in 20 exclusive multi-lepton channels for 222 independent production and decay topologies that arise for four benchmark 2HDM spectra within each parameter space. A comparison of these sensitivities with the results of a multi-lepton search conducted by the CMS collaboration using 5 fb−1 of data collected from 7 TeV pp collisions yields new limits in some regions of 2HDM parameter space that have not previously been covered by other types of direct experimental searches.

title: Recovering Particle Masses from Missing Energy Signatures with Displaced Tracks
abstract: If physics beyond the Standard Model contains metastable new particle states, its signatures may manifest themselves at the LHC through the presence of displaced vertices or displaced tracks. Such signatures are common in low-scale supersymmetry breaking scenarios as well as a host of other well-studied new physics models. Here we analyze the kinematics of dual cascade decays with missing energy resulting from a stable non-interacting new particle state at the bottom of the decay chain. We find that if the final step of the decay chain involves a metastable particle, the resulting presence of displaced tracks provides strong constraints with which to solve for the unknown kinematic quantities lost through missing energy. In addition we develop techniques with which to recover all kinematic unknowns, even in situations where the unknown quantities outnumber the constraints. These techniques can all be performed using a very small number of events and can thus be applied to very early discovery level searches at the LHC.

title: How (Not) to Palatini
abstract: We revisit the problem of defining non-minimal gravity in the first order formalism. Specializing to scalar-tensor theories, which may be disguised as ‘higher-derivative’ models with the gravitational Lagrangians that depend only on the Ricci scalar, we show how to recast these theories as Palatini-like gravities. The correct formulation utilizes the Lagrange multiplier method, which preserves the canonical structure of the theory, and yields the conventional metric scalar-tensor gravity. We explain the discrepancies between the näıve Palatini and the Lagrange multiplier approach, showing that the näıve Palatini approach really swaps the theory for another. The differences disappear only in the limit of ordinary General Relativity, where an accidental redundancy ensures that the näıve Palatini works there. We outline the correct decoupling limits and the strong coupling regimes. As a corollary we find that the so-called ‘Modified Source Gravity’ models suffer from strong coupling problems at very low scales, and hence cannot be a realistic approximation of our universe. We also comment on a method to decouple the extra scalar using the chameleon mechanism. iglesias@physics.ucdavis.edu kaloper@physics.ucdavis.edu antonio.padilla@nottingham.ac.uk park@physics.ucdavis.edu

title: Multi-lepton signals of the Higgs boson
abstract: A bstractThe possibility of searching for the Higgs boson in channels with multiple non-resonant leptons is evaluated in light of recent advances in multi-lepton search techniques at the LHC. The total multi-lepton Higgs signal exceeds the four lepton gold-plated resonant mode, but is spread over many channels with same-sign di-lepton, tri-lepton, and four lepton final states. While any individual channel alone is not significant, the exclusive combination across multiple channels is shown to provide a sensitivity nearly comparable to other discovery level searches for the Higgs boson. We estimate that with 5 fb−1 of data, existing non-optimized multi-lepton searches at the LHC could exclude the Higgs boson to 95 % CL at a few times the predicted Standard Model cross section in the mass range 120 − 150 GeV. Refinements focused specifically on the Higgs boson signal are suggested that would further increase sensitivity. We illustrate the possibility of discerning patterns in production and decay modes using correlations across multiple channels by comparing sensitivities to Standard Model, Fermi-phobic, and b-phobic Higgs bosons.

title: Simplified Models for LHC New Physics Searches
abstract: This document proposes a collection of simplified models relevant to the design of new-physics searches at the Large Hadron Collider (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 similar to 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.