arXiv subjects

Adam Martin

Publications and source records attributed to Adam Martin.

At least 91 records · Page 5Linked to original sources

arXiv2013

The Muon Collider as a $H/A$ factory

We show that a muon collider is ideally suited for the study of heavy H/A scalars, cousins of the Higgs boson found in two-Higgs doublet models and required in supersymmetric models. The key aspects of H/A are: (1) they are narrow, yet have a width-to-mass ratio far larger than the expected muon collider beam-energy resolution, and (2) the larger muon Yukawa allows efficient s-channel production. We study in detail a representative Natural Supersymmetry model which has a 1.5 Tev H/A with $m_H$- $m_A$ = 10 Gev. The large event rates at resonant peak allow the determination of the individual H and A resonance parameters (including CP) and the decays into electroweakinos provides a wealth of information unavailable to any other present or planned collider.

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arXiv2013

Natural Supersymmetry and Implications for Higgs physics

We re-analyze the LHC bounds on light third generation squarks in Natural Supersymmetry, where the sparticles have masses inversely proportional to their leading-log contributions to the electroweak symmetry breaking scale. Higgsinos are the lightest supersymmetric particles; top and bottom squarks are the next-to-lightest sparticles that decay into both neutral and charged Higgsinos with well-defined branching ratios determined by Yukawa couplings and kinematics. The Higgsinos are nearly degenerate in mass, once the bino and wino masses are taken to their natural (heavy) values. We consider three scenarios for the stop and sbottom masses: (I) $\tilde{t}_R$ is light, (II) $\tilde{t}_L$ and $\tilde{b}_L$ are light, and (III) $\tilde{t}_R$, $\tilde{t}_L$, and $\tilde{b}_L$ are light. Dedicated stop searches are currently sensitive to Scenarios II and III, but not Scenario I. Sbottom-motivated searches ($2 b + \rm{MET}$) impact both squark flavors due to $\tilde{t} \ra b \charp_1$ as well as $\tilde{b} \ra b \neut_{1,2}$, constraining Scenarios I and III with somewhat weaker constraints on Scenario II. The totality of these searches yield relatively strong constraints on Natural Supersymmetry. Two regions that remain are: (1) the "compressed wedge", where $(m_{\tilde{q}} - |μ|)/m_{\tilde{q}} \ll 1$, and (2) the "kinematic limit" region, where $m_{\tilde{q}} \gsim 600-750 GeV, at the kinematic limit of the LHC searches. We calculate the correlated predictions for Higgs physics, demonstrating that these regions lead to distinct predictions for the lightest Higgs couplings that are separable with $\simeq 10% measurements. We show that these conclusions remain largely unchanged once the MSSM is extended to the NMSSM in order to naturally obtain a large enough mass for the lightest Higgs boson consistent with LHC data.

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arXiv2013

A Higgs Impostor in Low-Scale Technicolor

We propose a "Higgs impostor" model for the 125 GeV boson, $X$, recently discovered at the LHC. It is a technipion, $η_T$, with $I^G J^{PC} = 0^- 0^{-+}$ expected in this mass region in low-scale technicolor. Its coupling to pairs of standard-model gauge bosons are dimension-five operators whose strengths are determined within the model. It is easy for the gluon fusion rate $σB(gg \to η_T \to γγ)$ to agree with the measured one, but $η_T \to ZZ^*,\,WW^*$ are greatly suppressed relative to the standard-model Higgs rates. This is a crucial test of our proposal. In this regard, we assess the most recent data on $X$ decay modes, with a critical discussion of $X \to ZZ^* \to 4\ell$. In our model the $η_T$ mixes almost completely with the isovector $π^0_T$, giving two similar states, $η_L$ at 125 Gev and $η_H$ higher, possibly in the range 170--190 Gev. Important consequences of this mixing are (1) the only associated production of et al is via $\to \to W η_L$, and this could be sizable; (2) $η_H$ may soon be accessible in $gg \to η_H \to γγ$; and (3) LSTC phenomenology at the LHC is substantially modified.

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arXiv2012

Data driving the top quark forward--backward asymmetry with a lepton-based handle

We propose that, within the standard model, the correlation between the $t\bar{t}$ forward--backward asymmetry $A_{t\bar t}$ and the corresponding lepton-based asymmetry $A_l$ -- at the differential level -- is strong and rather clean both theoretically and experimentally. Hence a combined measurement of the two distributions as a function of the lepton $p_T$, a direct and experimentally clean observable, would lead to a potentially unbiased and normalization-free test of the standard model prediction. To check the robustness of our proposal we study how the correlation is affected by mis-measurement of the $t\bar t$ system transverse momenta, acceptance cuts, scale dependence and compare the results of MCFM, POWHEG (with & without PYTHIA showering), and SHERPA's CSSHOWER in first-emission mode. We find that the shape of the relative differential distribution $A_{l} (p^{l}_{T}) [A_{t\bar{t}} (p^l_T)]$ is only moderately distorted hence supporting the usefulness of our proposal. Beyond the first emission, we find that the correlation is not accurately captured by lowest-order treatment. We also briefly consider other differential variables such as the system transverse mass and the canonical $t\bar t$ invariant mass. Finally, we study new physics scenarios where the correlation is significantly distorted and therefore can be more readily constrained or discovered using our method.

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arXiv2012

Discovering Strong Top Dynamics at the LHC

We analyze the phenomenology of the top-pion and top-Higgs states in models with strong top dynamics, and translate the present LHC searches for the Standard Model Higgs into bounds on these scalar states. We explore the possibility that the new state at a mass of approximately 125 GeV observed at the LHC is consistent with a neutral pseudoscalar top-pion state. We demonstrate that a neutral pseudoscalar top-pion can generate the diphoton signal at the observed rate. However, the region of model parameter space where this is the case does not correspond to classic topcolor-assisted technicolor scenarios with degenerate charged and neutral top-pions and a top-Higgs mass of order twice the top mass; rather, additional isospin violation would need to be present and the top dynamics would be more akin to that in top seesaw models. Moreover, the interpretation of the new state as a top-pion can be sustained only if the ZZ (four-lepton) and WW (two-lepton plus missing energy) signatures initially observed at the 3? level decline in significance as additional data is accrued.

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arXiv2012

Electroweak Baryogenesis in R-symmetric Supersymmetry

We demonstrate that electroweak baryogenesis can occur in a supersymmetric model with an exact R-symmetry. The minimal R-symmetric supersymmetric model contains chiral superfields in the adjoint representation, giving Dirac gaugino masses, and an additional set of "R-partner" Higgs superfields, giving R-symmetric μ-terms. New superpotential couplings between the adjoints and the Higgs fields can simultaneously increase the strength of the electroweak phase transition and provide additional tree-level contributions to the lightest Higgs mass. Notably, no light stop is present in this framework, and in fact, we require both stops to be above a few TeV to provide sufficient radiative corrections to the lightest Higgs mass to bring it up to 125 GeV. Large CP-violating phases in the gaugino/higgsino sector allow us to match the baryon asymmetry of the Universe with no constraints from electric dipole moments due to R-symmetry. We briefly discuss some of the more interesting phenomenology, particularly of the of the lightest CP-odd scalar.

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arXiv2012

Enhanced di-Higgs Production through Light Colored Scalars

We demonstrate enhanced di-Higgs production at the LHC in the presence of modifications of the effective couplings of Higgs to gluons from new, light, colored scalars. While our results apply to an arbitrary set of colored scalars, we illustrate the effects with a real color octet scalar -- a simple, experimentally viable model involving a light (~125-300 GeV) colored scalar. Given the recent LHC results, we consider two distinct scenarios: First, if the Higgs is indeed near 125 GeV, we show that the di-Higgs cross section could be up to nearly one thousand times the Standard Model rate for particular octet couplings and masses. This is potentially observable in \emph{single} Higgs production modes, such as $pp \to h h \to γγb\bar{b}$ as well as $pp \to h h \to τ^+τ^- b\bar{b}$ where a small fraction of the $γγ$ or $τ^+τ^-$ events near the putative Higgs invariant mass peak contain also a $b\bar{b}$ resonance consistent with the Higgs mass. Second, if the Higgs is not at 125 GeV (and what the LHC has observed is an impostor), we show that the same parameter region where singly-produced Higgs production can be suppressed below current LHC limits, for a heavier Higgs mass, also simultaneously predicts substantially enhanced di-Higgs production. We point out several characteristic signals of di-Higgs production with a heavier Higgs boson, such as $pp \to hh \to W^+W^-W^+W^-$, which could use same-sign dileptons or trileptons plus missing energy to uncover evidence.

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arXiv2012

Testing the Technicolor Interpretation of the CDF Dijet Excess at the 8-TeV LHC

Under the assumption that the dijet excess seen by the CDF Collaboration near 150 Gev in Wjj production is due to the lightest technipion of the low-scale technicolor process $ρ_T \rightarrow W π_T$, we study its observability in LHC detectors for 8 TeV collisions and 20 inverse femtobarns of integrated luminosity. We describe interesting new kinematic tests that can provide independent confirmation of this LSTC hypothesis. We show that cuts similar to those employed by CDF, and recently by ATLAS, cannot confirm the dijet signal. We propose cuts tailored to the LSTC hypothesis and its backgrounds at the LHC that may reveal $ρ_T \rightarrow \ellνjj$. Observation of the isospin-related channel $ρ^{\pm}_T \rightarrow Z π^{\pm}_T \rightarrow \ell^+\ell^- jj$ and of $ρ^{\pm}_T \rightarrow WZ$ in the $\ell^+\ell^-\ell^{pm}ν_\ell$ and $\ell^+\ell^- jj$ modes will be important confirmations of the LSTC interpretation of the CDF signal. The $Zπ_T$ channel is experimentally cleaner than $Wπ_T$ and its rate is known from $Wπ_T$ by phase space. It can be discovered or excluded with the collider data expected by the end of 2012. The $WZ \rightarrow 3\ellν$ channel is cleanest of all and its rate is determined from $Wπ_T$ and the LSTC parameter $\sinχ$. This channel and $WZ \to \ell^+\ell^- jj$ are discussed as a function of $\sinχ$.

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arXiv2012

Supersoft Supersymmetry is Super-Safe

We show that supersymmetric models with a large Dirac gluino mass can evade much of the jets plus missing energy searches at LHC. Dirac gaugino masses arise from "supersoft" operators that lead to finite one-loop suppressed contributions to the scalar masses. A little hierarchy between the Dirac gluino mass 5 - 10 times heavier than the squark masses is automatic and technically natural, in stark contrast to supersymmetric models with Majorana gaugino masses. At the LHC, colored sparticle production is suppressed not only by the absence of gluino pair (or associated) production, but also because several of the largest squark pair production channels are suppressed or absent. We recast the null results from the present jets plus missing energy searches at LHC for supersymmetry onto a supersoft supersymmetric simplified model (SSSM). Assuming a massless LSP, we find the strongest bounds are: 748 GeV from a 2j + MET search at ATLAS (4.7 fb^{-1}), and 684 GeV from a combined jets plus missing energy search using $α_T$ at CMS (1.1 fb^{-1}). In the absence of a future observation, we estimate the bounds on the squark masses to improve only modestly with increased luminosity. We also briefly consider the further weakening in the bounds as the LSP mass is increased.

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arXiv2012

Testing the Technicolor Interpretation of CDF's Dijet Excess at the LHC

Under the assumption that the dijet excess seen by the CDF Collaboration near 150 Gev in Wjj production is due to the lightest technipion of the low-scale technicolor process $ρ_T \rightarrow W π_T$, we study its observability in LHC detectors with 1--20 inverse femtobarns of data. We describe interesting new kinematic tests that can provide independent confirmation of this LSTC hypothesis. We find that cuts similar to those employed by CDF, and recently by ATLAS, cannot confirm the dijet signal. We propose cuts tailored to the LSTC hypothesis and its backgrounds at the LHC that may reveal $ρ_T \rightarrow \ellνjj$. Observation of the isospin-related channel $ρ^{pm}_T \rightarrow Z π^{pm}_T \rightarrow \ell^+ \ell^- jj$ and of $ρ^{pm}_T \rightarrow WZ$ in the three lepton plus neutrino and dilepton plus dijet modes will be important confirmations of the LSTC interpretation of the CDF signal. The $Zπ_T$ channel is experimentally cleaner than $Wπ_T$ and its rate is known from $Wπ_T$ by phase space. It can be discovered or excluded with the collider data expected in 2012. The $WZ \rightarrow 3\ellν$ channel is cleanest of all and its rate is determined from $Wπ_T$ and the LSTC parameter $\sinχ$. This channel and $WZ \rightarrow \ell^+\ell^- jj$ are discussed as a function of $\sinχ$.

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arXiv2012

Higgs Underproduction at the LHC

We show that production of the Higgs boson through gluon-fusion may be suppressed in the presence of colored scalars. Substantial destructive interference between the top quark diagrams and colored scalar diagrams is possible due to cancellations between the real (and also imaginary) parts of the amplitudes. As an example, we consider a color-octet scalar that has a negative, order one coupling to the Higgs doublet. We find that gluon fusion can be suppressed by more than an order of magnitude when the scalar mass is below a few hundred GeV, while milder suppressions occur for larger scalar masses or smaller couplings. Thus, the standard model extended with only one particle can evade the full range of present LHC exclusion limits on the Higgs mass. The colored scalars, however, would be produced in pairs with a large rate at the LHC, leading to multi-jet final states to which the LHC experiments are now becoming sensitive.

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arXiv2011

Topcolor in the LHC Era

Ongoing LHC searches for the standard model Higgs Boson in WW or ZZ decay modes strongly constrain the top-Higgs state predicted in many models with new dynamics that preferentially affects top quarks. Such a state couples strongly to top-quarks, and is therefore produced through gluon fusion at a rate that can be greatly enhanced relative to the rate for the standard model Higgs boson. As we discuss in this talk, a top-Higgs state with mass less than 300 GeV is excluded at 95% CL if the associated top-pion has a mass of 150 GeV, and the constraint is even stronger if the mass of the top-pion state exceeds the top-quark mass or if the top-pion decay constant is a substantial fraction of the weak scale. These results have significant implications for theories with strong top dynamics, such as topcolor-assisted technicolor, top-seesaw models, and certain Higgsless models.

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arXiv2011

Distinguishing among Technicolor/Warped Scenarios in Dileptons

Models of dynamical electroweak symmetry breaking usually include new spin-1 resonances, whose couplings and masses have to satisfy electroweak precision tests. We propose to use dilepton searches to probe the underlying structure responsible for satisfying these. Using the invariant mass spectrum and charge asymmetry, we can determine the number, parity, and isospin of these resonances. We pick three models of strong/warped symmetry breaking, and show that each model produces specific features that reflect this underlying structure of electroweak symmetry breaking and cancellations.

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arXiv2011

What the Tevatron Found?

The CDF collaboration has reported a 4.1σ excess in their lepton, missing energy, and dijets channel. This excess, which takes the form of an approximately Gaussian peak centered at a dijet invariant mass of 147 GeV, has provoked a great deal of experimental and theoretical interest. Although the DØ collaboration has reported that they do not observe a signal consistent with CDF, there is currently no widely accepted explanation for the discrepancy between these two experiments. A resolution of this issue is of great importance---not least because it may teach us lessons relevant for future searches at the LHC---and it will clearly require additional information. In this paper, we consider the ability of the Tevatron and LHC detectors to observe evidence associated with the CDF excess in a variety of channels. We also discuss the ability of selected kinematic distributions to distinguish between Standard Model explanations of the observed excess and various new physics scenarios.

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arXiv2011

Non-perturbative proton stability

Proton decay is a generic prediction of GUT models and is therefore an important channel to detect the existence of unification or to set limits on GUT models. Current bounds on the proton lifetime are around 10^33 years, which sets stringent limits on the GUT scale. These limits are obtained under `reasonable' assumptions about the size of the hadronic matrix elements. In this paper we present a non-perturbative calculation of the hadronic matrix elements within the chiral bag model of the proton. We argue that there is an exponential suppression of the matrix elements, due to non-perturbative QCD, that stifles proton decay by orders of magnitude -- potentially O(10^-10). This suppression is present for small quark masses and is due to the chiral symmetry breaking of QCD. Such a suppression has clear implications for GUT models and could resuscitate several scenarios.

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arXiv2011

LHC Limits on the Top-Higgs in Models with Strong Top-Quark Dynamics

LHC searches for the standard model Higgs Boson in WW or ZZ decay modes place strong constraints on the top-Higgs state predicted in many models with new dynamics preferentially affecting top quarks. Such a state couples strongly to top-quarks, and is therefore produced through gluon fusion at a rate enhanced relative to the rate for the standard model Higgs boson. A top-Higgs state with mass less than 300 GeV is excluded at 95% CL if the associated top-pion has a mass of 150 GeV, and the constraint is even stronger if the mass of the top-pion state exceeds the top-quark mass or if the top-pion decay constant is a substantial fraction of the weak scale. These results have significant implications for theories with strong top dynamics, such as topcolor-assisted technicolor, top-seesaw models, and certain Higgsless models.

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arXiv2011

Same bump, different channel: Higgs fakes from technicolor

Resonant production of a light, narrow techni-rho, followed by the decay $ρ_T \rightarrow W+π_T(jj)$ has been proposed as an explanation of the Wjj excess observed by CDF. If the $π_T$ decays to $τ+ν/τ^+ τ^-$ rather than to jets, subsequent leptonic $τ$ decay leads to $\ell^+\ell^- νν\barν\barν$, a final state that will be picked up by standard model $WW^{(*)} \rightarrow \ell^+\ell^-$ + MET Higgs searches. We point out that, for the same range of technicolor parameters required to fit the CDF Wjj excess, the correlated $\ell^+\ell^-$ + MET technicolor signal can have strength comparable to that of an intermediate-mass standard model Higgs boson, and therefore could be visible at the Tevatron or LHC.

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arXiv2011

Technicolor at the Tevatron

We propose that the 3.2 sigma excess at ~150 GeV in the dijet mass spectrum of W + jets reported by CDF is the technipion $π_T$ of low-scale technicolor. Its relatively large cross section is due to production of a narrow $Wjj$ resonance, the technirho, which decays to W + $π_T$. We discuss ways to enhance and strengthen the technicolor hypothesis and suggest companion searches at the Tevatron and LHC.

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