arXiv subjects

Marcela Carena

Publications and source records attributed to Marcela Carena.

At least 73 records · Page 4Linked to original sources

arXiv2012

Light Stau Phenomenology and the Higgs γγRate

Recently, an excess of events consistent with a Higgs boson with mass of about 125 GeV was reported by the CMS and ATLAS experiments. This Higgs boson mass is consistent with the values that may be obtained in minimal supersymmetric extensions of the Standard Model (SM), with both stop masses less than a TeV and large mixing. The apparently enhanced photon production rate associated with this potential Higgs signal may be the result of light staus with large mixing. Large stau mixing and large coupling of the staus to the SM-like Higgs boson may be obtained for large values of tan β, and moderate to large values of the Higgsino mass parameter, μ. We study the phenomenological properties of this scenario, including precision electroweak data, the muon anomalous magnetic moment, Dark Matter, and the evolution of the soft supersymmetry-breaking parameters to high energies. We also analyze the possible collider signatures of light third generation sleptons and demonstrate that it is possible to find evidence of their production at the 8 TeV and the 14 TeV LHC. The most promising channel is stau and tau sneutrino associated production, with the sneutrino decaying into a W boson plus a light stau.

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arXiv2012

The pMSSM Interpretation of LHC Results Using Rernormalization Group Invariants

The LHC has started to constrain supersymmetry-breaking parameters by setting bounds on possible colored particles at the weak scale. Moreover, constraints from Higgs physics, flavor physics, the anomalous magnetic moment of the muon, as well as from searches at LEP and the Tevatron have set additional bounds on these parameters. Renormalization Group Invariants (RGIs) provide a very useful way of representing the allowed parameter space by making direct connection with the values of these parameters at the messenger scale. Using a general approach, based on the pMSSM parametrization of the soft supersymmetry-breaking parameters, we analyze the current experimental constraints to determine the probability distributions for the RGIs. As examples of their application, we use these distributions to analyze the question of Gaugino Mass Unification and to probabilistically determine the parameters of General and Minimal Gauge Mediation with arbitrary Higgs mass parameters at the Messenger Scale.

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arXiv2012

A 125 GeV SM-like Higgs in the MSSM and the $γγ$ rate

We consider the possibility of a Standard Model (SM)-like Higgs in the context of the Minimal Supersymmetric Standard Model (MSSM), with a mass of about 125 GeV and with a production times decay rate into two photons which is similar or somewhat larger than the SM one. The relatively large value of the SM-like Higgs mass demands stops in the several hundred GeV mass range with somewhat large mixing, or a large hierarchy between the two stop masses in the case that one of the two stops is light. We find that, in general, if the heaviest stop mass is smaller than a few TeV, the rate of gluon fusion production of Higgs bosons decaying into two photons tends to be somewhat suppressed with respect to the SM one in this region of parameters. However, we show that an enhancement of the photon decay rate may be obtained for light third generation sleptons with large mixing, which can be naturally obtained for large values of $\tanβ$ and sizable values of the Higgsino mass parameter.

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arXiv2012

B Meson Mixing in Effective Theories of Supersymmetric Higgs Bosons

We study a minimal flavor violating extension of the MSSM, where higher dimensional operators in the Kahler potential induce tree level non-holomorphic Higgs couplings that are controlled by the scale of the physics beyond the MSSM, and analyze their possible impact on CP violation in Bs and Bd mixing. We consider results on the time dependent CP asymmetries in Bs --> psi phi and Bs --> psi f_0 from LHCb, in Bs --> psi phi from CDF and D0 and in B --> psi K_S from the B factories as well as the measurement of an anomalous like-sign dimuon charge asymmetry at D0. Taking into account the stringent bounds on the branching ratio of the rare Bs --> mu+mu- decay, we investigate to which extent the framework allows to address the observed (2-3)sigma discrepancies in fits of the unitarity triangle. We find that a non-standard Bd mixing phase, that is in agreement with the current bounds on CP violation in Bs mixing, requires the presence of higher dimensional operators both in the Kahler potential and the superpotential. The corresponding region of parameter space is characterized by small tan(beta)~5, a light Higgs spectrum with masses below ~400 GeV and will be probed by future measurements at LHCb.

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arXiv2011

Signals of CP Violation Beyond the MSSM in Higgs and Flavor Physics

We study an extension of the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM), considering the effects of new degrees of freedom at the TeV scale, and allowing for sources of CP violation beyond the MSSM (BMSSM). We analyze the impact of the BMSSM sources of CP violation on the Higgs collider phenomenology and on low energy flavor and CP violating observables. We identify distinct Higgs collider signatures that cannot be realized, either in the case without CP violating phases or in the CP violating MSSM, and investigate the prospects to probe them at the Tevatron and the LHC. The most striking benchmark scenario has three neutral Higgs bosons that all decay dominantly into W boson pairs and that are well within the reach of the 7 TeV LHC run. On the other hand, we also present scenarios with three Higgs bosons that have masses M_Hi > 150 GeV and decay dominantly into b bbar. Such scenarios are much more challenging to probe and can even lie completely outside the reach of the 7 TeV LHC run. We explore complementary scenarios with standard MSSM Higgs signals that allow to accommodate a sizable B_s mixing phase as indicated by D0, as well as the excess in B_s --> mu+ mu- candidates recently reported by CDF. We find that, in contrast to the MSSM, a minimal flavor violating soft sector is sufficient to generate significant corrections to CP violating observables in meson mixing, compatible with EDM constraints. In particular, a sizable B_s mixing phase, S_psiphi < 0.4, can be achieved for specific regions of parameter space. Such a large B_s mixing phase would unambiguously imply a sizable suppression of S_psiKs with respect to the SM prediction and a BR(B_s --> mu+ mu-) close to the 95% C.L. upper bound reported by CDF.

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arXiv2011

BMSSM Higgs Bosons at the 7 TeV LHC

We consider the Higgs sector in extensions of the Minimal Supersymmetric Standard Model by higher-dimension operators in the superpotential and the Kähler potential, in the context of Higgs searches at the LHC 7 TeV run. Such an effective field theory (EFT) approach, also referred to as BMSSM, allows for a model-independent description that may correspond to the combined effects of additional supersymmetric sectors, such as heavy singlets, triplets or gauge bosons, in which the supersymmetry breaking mass splittings can be treated as a perturbation. We consider the current LHC dataset, based on about $1-2 {\rm fb}^{-1}$ of data to set exclusion limits on a large class of BMSSM models. We also present projections for integrated luminosities of 5 and 15 fb$^{-1}$, assuming that the ATLAS and CMS collaborations will combine their results in each channel. Our study shows that the majority of the parameter space will be probed at the $2σ$ level with 15 fb$^{-1}$ of data. A non-observation of a Higgs boson with about 10 fb$^{-1}$ of data will point towards a Higgs SUSY spectrum with intermediate $\tan β$ ($\approx$ a few to 10) and a light SM-like Higgs with somewhat enhanced couplings to bottom and tau pairs. We define a number of BMSSM benchmark scenarios and analyze the possible exclusion/discovery channels and the projected required luminosity to probe them. We also discuss the results of the EFT framework for two specific models, one with a singlet superfield and one with SU(2)$_L$ triplets.

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arXiv2011

Light Dark Matter and the Electroweak Phase Transition in the NMSSM

We analyze the stability of the vacuum and the electroweak phase transition in the NMSSM close to the Peccei-Quinn symmetry limit. This limit contains light Dark Matter (DM) particles with a mass significantly smaller than the weak scale and also light CP-even and CP-odd Higgs bosons. Such light particles lead to a consistent relic density and facilitate a large spin-independent direct DM detection cross section, that may accommodate the recently reported signatures at the DAMA and CoGeNT experiments. Studying the one-loop effective potential at finite temperature, we show that when the lightest CP-even Higgs mass is of the order of a few GeV, the electroweak phase transition tends to become first order and strong. The inverse relationship between the direct-detection cross-section and the lightest CP-even Higgs mass implies that a cross-section of the order of 10$^{-41}$ cm$^2$ is correlated with a strong first order phase transition.

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arXiv2011

The 7 TeV LHC Reach for MSSM Higgs Bosons

The search for the Higgs boson is entering a decisive phase. The Large Hadron Collider experiments have collected more than 1 fb$^{-1}$ of data and are now capable of efficiently probing the high Higgs mass region, $m_H > 140$ GeV. The low mass region is more challenging at the LHC, but if the Higgs has Standard Model (SM)-like properties, the LHC should find evidence for it by the end of next year. In low energy supersymmetric extensions of the SM, the situation is similar for large values of the CP-odd Higgs mass $m_A$, but more interesting for lower values of $m_A$. The ($\sqrt{s}$ =7 TeV) LHC searches for a low-mass Standard Model Higgs boson predominantly in the $h\rightarrow γγ,WW$ decay modes, which may be suppressed by an increase in the $h\rightarrow b\bar{b}, τ^+ τ^-$ partial widths (and thus the total $h$ width) for $m_A\lesssim 500$ GeV. Although $h\rightarrow b\bar{b}, τ^+ τ^-$ are sought at the LHC, these channels are not powerful enough to fully counter this suppression in the first year of running. We consider two alternative possibilities for probing the low $m_A$ region: nonstandard Higgs boson searches at the LHC, and a statistical combination with the Tevatron, where $Vh\rightarrow b\bar{b}$ is the primary search channel for light $h$. We also study an MSSM scenario in which the $h\rightarrowγγ$ rate is enhanced at low $m_A$ to the point where discovery is possible in the near future.

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arXiv2011

W plus two jets from a quasi-inert Higgs doublet

We show that, the result recently reported by the CDF collaboration showing an excess in the invariant mass distribution of jet pairs produced in association with a W-boson can be explained by a simple extension of the Standard Model (SM) with an additional quasi-inert Higgs doublet. The two additional neutral Higgs states H^0 and A^0 have a mass of about 150 GeV and decay into a pair of jets. W^\pm H^0/A^0 pairs are produced from the decay of the heavier charged Higgs boson H^\pm. Depending on the precise masses of the neutral and charged Higgs bosons, the model is shown to be in agreement with constraints from electroweak precision tests and from flavor physics for a broad range of the Standard Model-like Higgs mass from 100 GeV to several hundreds of GeV. Other possible signals of this model at the Tevatron and the LHC are discussed.

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arXiv2011

SUSY-Breaking Parameters from RG Invariants at the LHC

We study Renormalization Group invariant (RGI) quantities in the Minimal Supersymmetric Standard Model and show that they are a powerful and simple instrument for testing high scale models of supersymmetry (SUSY)-breaking. For illustration, we analyze the frameworks of minimal and general gauge mediated (MGM and GGM) SUSY-breaking, with additional arbitrary soft Higgs mass parameters at the messenger scale. We show that if a gaugino and two first generation sfermion soft masses are determined at the LHC, the RGIs lead to MGM sum rules that yield accurate predictions for the other gaugino and first generation soft masses. RGIs can also be used to reconstruct the fundamental MGM parameters (including the messenger scale), calculate the hypercharge D-term, and find relationships among the third generation and Higgs soft masses. We then study the extent to which measurements of the full first generation spectrum at the LHC may distinguish different SUSY-breaking scenarios. In the case of MGM, although most deviations violate the sum rules by more than estimated experimental errors, we find a 1-parameter family of GGM models that satisfy the constraints and produce the same first generation spectrum. The GGM-MGM degeneracy is lifted by differences in the third generation masses and the messenger scales.

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arXiv2011

Model-Independent Searches for New Quarks at the LHC

New vector-like quarks can have sizable couplings to first generation quarks without conflicting with current experimental constraints. The coupling with valence quarks and unique kinematics make single production the optimal discovery process. We perform a model-independent analysis of the discovery reach at the Large Hadron Collider for new vector-like quarks considering single production and subsequent decays via electroweak interactions. An early LHC run with 7 TeV center of mass energy and 1 fb-1 of integrated luminosity can probe heavy quark masses up to 1 TeV and can be competitive with the Tevatron reach of 10 fb-1. The LHC with 14 TeV center of mass energy and 100 fb-1 of integrated luminosity can probe heavy quark masses up to 3.7 TeV for order one couplings.

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arXiv2010

Probing the Higgs Sector of High-Scale SUSY-Breaking Models at the Tevatron

A canonical signature of the Minimal Supersymmetric Standard Model (MSSM) is the presence of a neutral Higgs boson with mass bounded from above by about 135 GeV and Standard Model (SM)-like couplings to the electroweak gauge bosons. In this note we investigate the reach of the Tevatron collider for the MSSM Higgs sector parameter space associated with a variety of high-scale minimal models of supersymmetry (SUSY)-breaking, including the Constrained MSSM (CMSSM), minimal Gauge Mediated SUSY-breaking (mGMSB), and minimal Anomaly Mediated SUSY-breaking (mAMSB). We find that the Tevatron can provide strong constraints on these models via Higgs boson searches. Considering a simple projection for the efficiency improvements in the Tevatron analyses, we find that with an integrated luminosity of 16 fb^-1 per detector and an efficiency improvement of 20% compared to the present situation, these models could be probed essentially over their entire ranges of validity. With 40% analysis improvements and 16 fb^-1, our projection shows that evidence at the 3-sigma level for the light Higgs boson could be expected in extended regions of parameter space.

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arXiv2010

Determining the Structure of Supersymmetry-Breaking with Renormalization Group Invariants

If collider experiments demonstrate that the Minimal Supersymmetric Standard Model (MSSM) is a good description of nature at the weak scale, the experimental priority will be the precise determination of superpartner masses. These masses are governed by the weak scale values of the soft supersymmetry (SUSY)-breaking parameters, which are in turn highly dependent on the SUSY-breaking scheme present at high scales. It is therefore of great interest to find patterns in the soft parameters that can distinguish different high scale SUSY-breaking structures, identify the scale at which the breaking is communicated to the visible sector, and determine the soft breaking parameters at that scale. In this work, we demonstrate that 1-loop Renormalization Group~(RG) invariant quantities present in the MSSM may be used to answer each of these questions. We apply our method first to generic flavor-blind models of SUSY-breaking, and then examine in detail the subset of these models described by General Gauge Mediation and the constrained MSSM with non-universal Higgs masses. As RG invariance generally does not hold beyond leading-log order, we investigate the magnitude and direction of the 2-loop corrections. We find that with superpartners at the TeV scale, these 2-loop effects are either negligible, or they are of the order of optimistic experimental uncertainties and have definite signs, which allows them to be easily accounted for in the overall uncertainty.

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arXiv2010

BMSSM Higgs Bosons at the Tevatron and the LHC

We study extensions of the Minimal Supersymmetric Standard Model (MSSM) with new degrees of freedom that couple sizably to the MSSM Higgs sector and lie in the TeV range. After integrating out the physics at the TeV scale, the resulting Higgs spectrum can significantly differ from typical supersymmetric scenarios, thereby providing a window Beyond the MSSM (BMSSM). Taking into account current LEP and Tevatron constraints, we perform an in-depth analysis of the Higgs collider phenomenology and explore distinctive characteristics of our scenario with respect to both the Standard Model and the MSSM. We propose benchmark scenarios to illustrate specific features of BMSSM Higgs searches at the Tevatron and the LHC.

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arXiv2010

SUSY Higgs bosons and beyond

We consider extensions of the Minimal Supersymmetric Standard Model (MSSM) where the extra degrees of freedom interact weakly with the Higgs sector. These models allow to relax the tension between the lower bound on the lightest CP even Higgs mass from direct LEP searches and the theoretical upper bound of the MSSM. We study the beyond MSSM (BMSSM) effects via an effective field-theory approach, assuming that the MSSM is valid up to a heavy physics scale M. We compute the masses, couplings and branching fractions of the Higgs sector, including all the relevant corrections up to order 1/M^2. We find that the collider phenomenology can be greatly different with respect to both the SM and the MSSM.

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arXiv2010

The Planck Scale from Top Condensation

We propose a scenario in which the Planck scale is dynamically linked to the electroweak scale induced by top condensation. The standard model field content, without the Higgs, is promoted to a 5D warped background. There is also an additional 5D fermion with the quantum numbers of the right-handed top. Localization of the zero-modes leads, at low energies, to a Nambu-Jona-Lasinio model that also stabilizes the radion field dynamically thus explaining the hierarchy between the Planck scale and v_EW = 174 GeV. The top mass arises dynamically from the electroweak breaking condensate. The other standard model fermion masses arise naturally from higher-dimension operators, and the fermion mass hierarchies and flavor structure can be explained from the localization of the zero-modes in the extra dimension. If any other contributions to the radion potential except those directly related with electroweak symmetry breaking are engineered to be suppressed, the KK scale is predicted to be about two orders of magnitude above the electroweak scale rendering the model easily consistent with electroweak precision data. The model predicts a heavy (composite) Higgs with a mass of about 500 GeV and standard-model-like properties, and a vector-like quark with non-negligible mixing with the top quark and mass in the 1.6 - 2.9 TeV range. Both can be within the reach of the LHC. It also predicts a radion with a mass of a few GeV that is very weakly coupled to standard model matter.

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arXiv2010

Dilaton-assisted Dark Matter

A dilaton could be the dominant messenger between Standard Model fields and dark matter. The measured dark matter relic abundance relates the dark matter mass and spin to the conformal breaking scale. The dark matter-nucleon spin-independent cross section is predicted in terms of the dilaton mass. We compute the current constraints on the dilaton from LEP and Tevatron experiments, and the gamma-ray signal from dark matter annihilation to dilatons that could be observed by Fermi-LAT.

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arXiv2009

Supersymmetric Higgs Bosons and Beyond

We consider supersymmetric models that include particles beyond the Minimal Supersymmetric Standard Model (MSSM) with masses in the TeV range, and that couple significantly to the MSSM Higgs sector. We perform a model-independent analysis of the spectrum and couplings of the MSSM Higgs fields, based on an effective theory of the MSSM degrees of freedom. The tree-level mass of the lightest CP-even state can easily be above the LEP bound of 114 GeV, thus allowing for a relatively light spectrum of superpartners, restricted only by direct searches. The Higgs spectrum and couplings can be significantly modified compared to the MSSM ones, often allowing for interesting new decay modes. We also observe that the gluon fusion production cross section of the SM-like Higgs can be enhanced with respect to both the Standard Model and the MSSM.

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