arXiv subjects

Carlos E. M. Wagner

Publications and source records attributed to Carlos E. M. Wagner.

At least 91 records · Page 5Linked to original sources

arXiv2011

Dark Light Higgs

We study a limit of the nearly-Peccei-Quinn-symmetric Next-to-Minimal Supersymmetric Standard Model possessing novel Higgs and dark matter (DM) properties. In this scenario, there naturally co-exist three light singlet-like particles: a scalar, a pseudoscalar, and a singlino-like DM candidate, all with masses of order 0.1-10 GeV. The decay of a Standard Model-like Higgs boson to pairs of the light scalars or pseudoscalars is generically suppressed, avoiding constraints from collider searches for these channels. For a certain parameter window annihilation into the light pseudoscalar and exchange of the light scalar with nucleons allow the singlino to achieve the correct relic density and a large direct detection cross section consistent with the CoGeNT and DAMA/LIBRA preferred region simultaneously. This parameter space is consistent with experimental constraints from LEP, the Tevatron, and Upsilon- and flavor physics.

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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

Search for Higgs Bosons in SUSY Cascade Decays and Neutralino Dark Matter

The Minimal Supersymmetric Extension of the Standard Model (MSSM) is a well motivated theoretical framework, which contains an extended Higgs sector, including a light Higgs with Standard Model-like properties in most of the parameter space. Due to the large QCD background, searches for such a Higgs, decaying into a pair of bottom quarks, is very challenging at the LHC. It has been long realized that the situation may be ameliorated by searching for Higgs bosons in supersymmetric decay chains. Moreover, it has been recently suggested that the bobber decay channel may be observed in standard production channels by selecting boosted Higgs bosons, which may be easily identified from the QCD background. Such boosted Higgs bosons are frequent in the MSSM, since they are produced from decays of heavy colored supersymmetric particles. Previous works have emphasized the possibility of observing boosted Higgs bosons in the light higgsino region. In this work, we study the same question in the regions of parameter space consistent with a neutralino dark matter relic density, analyzing its dependence on the non-standard Higgs boson, slepton and squark masses, as well as on the condition of gaugino mass unification. In general, we conclude that, provided sleptons are heavier than the second lightest neutralinos, the presence of boosted Higgs is a common MSSM feature, implying excellent prospects for observation of the light MSSM Higgs boson 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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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

Forward-Backward Asymmetry of Top Quark Pair Production

We adopt a Markov Chain Monte Carlo method to examine various new physics models which can generate the forward-backward asymmetry in top quark pair production observed at the Tevatron by the CDF Collaboration. We study the following new physics models: (1) exotic gluon $G^\prime$, (2) extra $Z^\prime$ boson with flavor-conserving interaction, (3) extra $Z^\prime$ with flavor-violating $u$-$t$-$Z^\prime$ interaction, (4) extra $W^\prime$ with flavor-violating $d$-$t$-$W^\prime$ interaction, and (5) extra scalars $S$ and $S^\pm$ with flavor-violating $u$-$t$-$S$ and $d$-$t$-$S^\pm$ interactions. After combining the forward-backward asymmetry with the measurement of the top pair production cross section and the $t\bar{t}$ invariant mass distribution at the Tevatron, we find that an axial vector exotic gluon $G^\prime$ of mass about $1 {\rm TeV}$ or $2 {\rm TeV}$ or a $W^\prime$ of mass about $2 {\rm TeV}$ offer an improvement over the Standard Model. The other models considered do not fit the data significantly better than the Standard Model. We also emphasize a few points which have been long ignored in the literature for new physics searches: (1) heavy resonance width effects, (2) renormalization scale dependence, and (3) NLO corrections to the $t\bar{t}$ invariant mass spectrum. We argue that these three effects are crucial to test or exclude new physics effects in the top quark pair asymmetry.

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arXiv2010

Prospects for Higgs Searches at the Tevatron and LHC in the MSSM with Explicit CP-violation

We analyze the Tevatron and Large Hadron Collider (LHC) reach for the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM) in the presence of explicit CP-violation. Using the most recent studies from the Tevatron and LHC collaborations, we examine the CPX benchmark scenario for a range of CP-violating phases in the soft trilinear and gluino mass terms and compute the exclusion/discovery potentials for each collider on the $(M_{H^+}, \tanβ)$ plane. Projected results from Standard Model (SM)-like, non-standard, and charged Higgs searches are combined to maximize the statistical significance. We exhibit complementarity between the SM-like Higgs searches at the LHC with low luminosity and the Tevatron, and estimate the combined reach of the two colliders in the early phase of LHC running.

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arXiv2009

Prospects for MSSM Higgs Searches at the Tevatron

We analyze the Tevatron reach for neutral Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM), using current exclusion limits on the Standard Model Higgs. We study four common benchmark scenarios for the soft supersymmetry-breaking parameters of the MSSM, including cases where the Higgs decays differ significantly from the Standard Model, and provide projections for the improvements in luminosity and efficiency required for the Tevatron to probe sizeable regions of the $(m_A, \tanβ)$ plane.

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arXiv2009

$b \to s$ Transitions in Family-dependent $U(1)^\prime$ Models

We analyze flavor-changing-neutral-current (FCNC) effects in the $b\to s$ transitions that are induced by family non-universal $U(1)'$ gauge symmetries. After systematically developing the necessary formalism, we present a correlated analysis for the $ΔB =1, 2$ processes. We adopt a model-independent approach in which we only require family-universal charges for the first and second generations and small fermion mixing angles. We analyze the constraints on the resulting parameter space from $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (π, ϕ, η', ρ, ω, f_0)K_S$ decays. Our results indicate that the currently observed discrepancies in some of these modes with respect to the Standard Model predictions can be consistently accommodated within this general class of models.

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arXiv2009

Family Non-universal $U(1)^\prime$ Gauge Symmetries and $b\to s$ Transitions

We present a correlated analysis for the $ΔB =1, 2$ processes which occur via $b\to s$ transitions within models with a family non-universal $U(1)^\prime$. We take a model-independent approach, and only require family universal charges for the first and second generations and small fermion mixing angles. The results of our analysis show that within this class of models, the anomalies in $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (π, ϕ, η', ρ, ω, f_0)K_S$ decays can be accommodated.

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arXiv2009

A Heavy Higgs and a Light Sneutrino NLSP in the MSSM with Enhanced SU(2) D-terms

The Minimal Supersymmetric extension of the Standard Model provides a solution to the hierarchy problem and leads to the presence of a light Higgs. A Higgs boson with mass above the present experimental bound may only be obtained for relatively heavy third generation squarks, requiring a precise, somewhat unnatural balance between different contributions to the effective Higgs mass parameter. It was recently noticed that somewhat heavier Higgs bosons, which are naturally beyond the LEP bound, may be obtained by enhanced weak SU(2) D-terms. Such contributions appear in models with an enhanced electroweak gauge symmetry, provided the supersymmetry breaking masses associated with the scalars responsible for the breakdown of the enhanced gauge symmetry group to the Standard Model one, are larger than the enhanced symmetry breaking scale. In this article we emphasize that the enhanced SU(2) D-terms will not only raise the Higgs boson mass but also affect the spectrum of the non-standard Higgs bosons, sleptons and squarks, which therefore provide a natural contribution to the T parameter, compensating for the negative one coming from the heavy Higgs boson. The sleptons and non-standard Higgs bosons of these models, in particular, may act in a way similar to the so-called inert Higgs doublet. The phenomenological properties of these models are emphasized and possible cosmological implications as well as collider signatures are described.

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arXiv2009

Gauge-Higgs Unification, Neutrino Masses and Dark Matter in Warped Extra Dimensions

Gauge Higgs Unification in Warped Extra Dimensions provides an attractive solution to the hierarchy problem. The extension of the Standard Model gauge symmetry to $SO(5)xU(1)_X$ allows the incorporation of the custodial symmetry $SU(2)_R$ plus a Higgs boson doublet with the right quantum numbers under the gauge group. In the minimal model, the Higgs mass is in the range 110-150 GeV, while a light Kaluza Klein (KK) excitation of the top quark appears in the spectrum, providing agreement with precision electroweak measurements and a possible test of the model at a high luminosity LHC. The extension of the model to the lepton sector has several interesting features. We discuss the conditions necessary to obtain realistic charged lepton and neutrino masses. After the addition of an exchange symmetry in the bulk, we show that the odd neutrino KK modes provide a realistic dark matter candidate, with a mass of the order of 1 TeV, which will be probed by direct dark matter detection experiments in the near future.

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arXiv2008

The Baryogenesis Window in the MSSM

Electroweak baryogenesis provides an attractive explanation of the origin of the matter-antimatter asymmetry that relies on physics at the weak scale and thus it is testable at present and near future high-energy physics experiments. Although this scenario may not be realized within the Standard Model, it can be accommodated within the MSSM provided there are new CP-violating phases and the lightest stop mass is smaller than the top-quark mass. In this work we provide an evaluation of the values of the stop (m_{\tilde t}) and Higgs (m_H) masses consistent with the requirements of electroweak baryogenesis based on an analysis that makes use of the renormalization group improved Higgs and stop potentials, and including the dominant two-loop effects at high temperature. We find an allowed window in the (m_{\tilde t},m_H)-plane, consistent with all present experimental data, where there is a strongly first-order electroweak phase transition and where the electroweak vacuum is metastable but sufficiently long-lived. In particular we obtain absolute upper bounds on the Higgs and stop masses, m_H\lesssim 127 GeV and m_{\tilde t}\lesssim 120 GeV, implying that this scenario will be probed at the LHC.

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arXiv2008

The Effective Theory of the Light Stop Scenario

Electroweak baryogenesis in the minimal supersymmetric extension of the Standard Model may be realized within the light stop scenario, where the right-handed stop mass remains close to the top-quark mass to allow for a sufficiently strong first order electroweak phase transition. All other supersymmetric scalars are much heavier to comply with the present bounds on the Higgs mass and the electron and neutron electric dipole moments. Heavy third generation scalars render it necessary to resum large logarithm contributions to perform a trustable Higgs mass calculation. We have studied the one--loop RGE improved effective theory below the heavy scalar mass scale and obtained reliable values of the Higgs mass. Moreover, assuming a common mass $\tilde m$ for all heavy scalar particles, and values of all gaugino masses and the Higgsino mass parameter about the weak scale, and imposing gauge coupling unification, a two-loop calculation yields values of the mass $\tilde m$ in the interval between three TeV and six hundred TeV. Furthermore for a stop mass around the top quark mass, this translates into an upper bound on the Higgs mass of about 150 GeV. The Higgs mass bound becomes even stronger, of about 129 GeV, for the range of stop and gaugino masses consistent with electroweak baryogenesis. The collider phenomenology implications of this scenario are discussed in some detail.

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arXiv2008

Collider Phenomenology of Gauge-Higgs Unification Scenarios in Warped Extra Dimensions

We compute the couplings of the zero modes and first excited states of gluons, $W$'s, $Z$ gauge bosons, as well as the Higgs, to the zero modes and first excited states of the third generation quarks, in an RS Gauge-Higgs unification scenario based on a bulk $SO(5)\times U(1)_X$ gauge symmetry, with gauge and fermion fields propagating in the bulk. Using the parameter space consistent with electroweak precision tests and radiative electroweak symmetry breaking, we study numerically the dependence of these couplings on the parameters of our model. Furthermore, after emphasizing the presence of light excited states of the top quark, which couple strongly to the Kaluza Klein gauge bosons, the associated collider phenomenology is analyzed. In particular, we concentrate on the possible detection of the first excited state of the top, $t^1$, which tends to have a higher mass than the ones accessible via regular QCD production processes. We stress that the detection of these particles is still possible due to an increase in the pair production of $t^1$ induced by the first excited state of the gluon, $G^1$.

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arXiv2008

Dynamically Solving the $μ/B_μ$ Problem in Gauge-mediated Supersymmetry Breaking

We provide a simple solution to the $μ/B_μ$ problem in the gauge-mediated Next-to-Minimal Supersymmetric Standard Model. In this model the messenger sector contains one pair of $3+\bar 3$ and one pair of $2+\bar 2$ messengers. These two messenger pairs couple to different gauge singlets in the hidden sector in which supersymmetry (SUSY) is broken. Such a gauge-mediation structure can naturally arise in many backgrounds. Because of the two effective SUSY breaking scales $\frac{< F_i>}{< M_i>}$ in the messenger sector, the renormalization group evolutions of the soft SUSY breaking parameters can be properly modified, leading to a negative enough singlet soft mass square $m_N^2(Λ_{EW})$ and hence reasonable $μ/B_μ$ values. In most of the perturbative (up to the GUT scale) parameter region, as a result, the electroweak scale is stabilized and phenomenologically interesting mass spectra of particles and superparticles are obtained. In addition, this model favors large values of $\tanβ$: $5 \sim 50$ and a heavy scalar spectrum. With the relatively large $\tanβ$, the light $U(1)_R$ pseudoscalar (mainly appearing in the low-scale gauge-mediated SUSY breaking models) becomes extremely singlet-like, and is no longer a problem in this model. These features apply to all cases of low-, intermediate- and high-scale gauge-mediated SUSY breaking.

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