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At least 1,045 records · Page 58
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DOE OSTI2010

Supergravity Higgs inflation and shift symmetry in electroweak theory

We present a model of inflation in a supergravity framework in the Einstein frame where the Higgs field of the next to minimal supersymmetric standard model (NMSSM) plays the role of the inflaton. Previous attempts which assumed non-minimal coupling to gravity failed due to a tachyonic instability of the singlet field during inflation. A canonical Kähler potential with minimal coupling to gravity can resolve the tachyonic instability but runs into the η-problem. We suggest a model which is free of the η-problem due to an additional coupling in the Kähler potential which is allowed by the Standard Model gauge group. This induces directions in the potential which we call K-flat. For a certain value of the new coupling in the (N)MSSM, the Kähler potential is special, because it can be associated with a certain shift symmetry for the Higgs doublets, a generalization of the shift symmetry for singlets in earlier models. We find that K-flat direction has H{sub u}{sup 0} = −H{sub d}{sup 0*}. This shift symmetry is broken by interactions coming from the superpotential and gauge fields. This flat direction fails to produce successful inflation in the MSSM but yields a more interesting model in the NMSSM, even though it does not pass existing cosmological constraints. We point out that, in building more sophisticated models of this type, one may also need to take into account their implications for axion searches or other elementary particle constraints.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Exploring SUSY light Higgs boson scenarios via dark matter experiments

We examine the dark matter phenomenology in supersymmetric light higgs boson scenarios, adapting nonuniversal Higgs masses at the gauge coupling unification scale. The correct relic density is obtained mostly through the annihilation into a pseudoscalar A, which gives high values for the self-annihilation cross-section at present times. Our analysis shows that most part of the A pole region can produce detectable gamma-rays and antiproton signals, and still be compatible with with recent direct detection data from XENON100 and CDMS-II.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Updated global fits of the cMSSM including the latest LHC SUSY and Higgs searches and XENON100 data

We present new global fits of the constrained Minimal Supersymmetric Standard Model (cMSSM), including LHC 1/fb integrated luminosity SUSY exclusion limits, recent LHC 5/fb constraints on the mass of the Higgs boson and XENON100 direct detection data. Our analysis fully takes into account astrophysical and hadronic uncertainties that enter the analysis when translating direct detection limits into constraints on the cMSSM parameter space. We provide results for both a Bayesian and a Frequentist statistical analysis. We find that LHC 2011 constraints in combination with XENON100 data can rule out a significant portion of the cMSSM parameter space. Our results further emphasise the complementarity of collider experiments and direct detection searches in constraining extensions of Standard Model physics. The LHC 2011 exclusion limit strongly impacts on low-mass regions of cMSSM parameter space, such as the stau co-annihilation region, while direct detection data can rule out regions of high SUSY masses, such as the Focus-Point region, which is unreachable for the LHC in the near future. We show that, in addition to XENON100 data, the experimental constraint on the anomalous magnetic moment of the muon plays a dominant role in disfavouring large scalar and gaugino masses. We find that, should the LHC 2011 excess hinting towards a Higgs boson at 126 GeV be confirmed, currently favoured regions of the cMSSM parameter space will be robustly ruled out from both a Bayesian and a profile likelihood statistical perspective.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

GUT scalar potentials for Higgs inflation

Motivated by the idea that there is new physics beyond the Standard Model (SM), we have investigated a number of models for Grand Unified Theories (GUTS) in four dimensions for the possibility that their Higgs fields might be responsible for inflation in the early universe. In addition to models having an intrinsic Planck mass parameter, we have entertained classically scale invariant models in which the Planck scale itself as well as the GUT scale is induced by spontaneous breaking of the gauge symmetry. We found that in non-supersymmetric SU(5) with the usual Higgs in the adjoint representation but with large non-minimal coupling to the curvature, there appear to be several possible flat directions that might lead to inflation. Interestingly, the one of lowest energy is the breaking into SU(3)SU(2)U(1) that is suggested by gauge coupling unification. Further, we show that this flat direction is stable against small fluctuations in other directions. We attempted to extend this to similar supersymmetric GUTS, both global and supergravity, but did not succeed in finding a phenomenologically acceptable model of this type, with a 'minimal' Kaehler potential augmented only by terms characterised by dimensionless coupling constants. As is often the case, such models suffered either from a negative vacuum energy or from tachyonic modes. We also considered a variant of an 'inverted hierarchy' model in which the GUT scale is set by dimensional transmutation, but were unable to find a phenomenologically acceptable model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Electroweak baryogenesis and dark matter from a singlet Higgs

If the Higgs boson H couples to a singlet scalar S via λ{sub m}|H|{sup 2}S{sup 2}, a strong electroweak phase transition can be induced through a large potential barrier that exists already at zero temperature. In this case properties of the phase transition can be computed analytically. We show that electroweak baryogenesis can be achieved using CP violation from a dimension-6 operator that couples S to the top-quark mass, suppressed by a new physics scale that can be well above 1 TeV. Moreover the singlet is a dark matter candidate whose relic density is ∼<3% of the total dark matter density, but which nevertheless interacts strongly enough with nuclei (through Higgs exchange) to be just below the current XENON100 limits. The DM mass is predicted to be in the range 80–160 GeV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Non-Gaussianities from the Standard Model Higgs

We have recently proposed that the Standard Model Higgs might be responsible for generating the cosmological perturbations of the universe by acting as an isocurvature mode during a de Sitter inflationary stage. In this paper we study the level of non-Gaussianity in the cosmological perturbations which are inevitably generated due to the non-linearities of the Standard Model Higgs potential. In particular, for the current central value of the top mass, we find that a future detection of non-Gaussianity would exclude the detection of tensor modes by the PLANCK satellite.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Gravitino decays and the cosmological lithium problem in light of the LHC Higgs and supersymmetry searches

We studied previously the impact on light-element abundances of gravitinos decaying during or after Big-Bang nucleosynthesis (BBN). We found regions of the gravitino mass m{sub 3/2} and abundance ζ{sub 3/2} plane where its decays could reconcile the calculated abundance of {sup 7}Li with observation without perturbing the other light-element abundances unacceptably. Here we revisit this issue in light of LHC measurements of the Higgs mass and constraints on supersymmetric model parameters, as well as updates in the astrophysical measurements of light-element abundances. In addition to the constrained minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking masses at the GUT scale (the CMSSM) studied previously, we also study models with universality imposed below the GUT scale and models with non-universal Higgs masses (NUHM1). We calculate the total likelihood function for the light-element abundances, taking into account the observational uncertainties. We find that gravitino decays provide a robust solution to the cosmological {sup 7}Li problem along strips in the (m{sub 3/2},ζ{sub 3/2}) plane along which the abundances of deuterium, {sup 4}He and {sup 7}Li may be fit with χ{sup 2}{sub min}∼<3, compared with χ{sup 2} ∼ 34 if the effects of gravitino decays are unimportant. The minimum of the likelihood function is reduced to χ{sup 2} < 2 when the uncertainty on D/H is relaxed and < 1 when the lithium abundance is taken from globular cluster data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Right-handed sneutrinos as asymmetric DM and neutrino masses from neutrinophilic Higgs bosons

We consider an extension of the Next-to-Minimal Supersymmetric Standard Model by three right-handed neutrinos and a pair of neutrinophilic Higgs superfields. The small neutrino masses arise naturally from a small vacuum expectation value of the additional Higgs fields (hence without lepton number violation), while the lightest right-handed sneutrinos can constitute asymmetric Dark Matter. The right-handed sneutrino and baryon asymmetries are connected through equilibrium processes in the early universe, explaining the coincidence of the DM and baryon abundances. We show that particle physics and astrophysical constraints are satisfied.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Enhancement of Majorana dark matter annihilation through Higgs bremsstrahlung

For Majorana dark matter, gauge boson bremsstrahlung plays an important role in enhancing an otherwise helicity-suppressed s-wave annihilation cross-section. This is well known for processes involving a radiated photon or gluon together with a Standard Model fermion-antifermion pair, and the case of massive electroweak gauge bosons has also recently been studied. Here we show that internal Higgs bremsstrahlung also lifts helicity suppression and could be the dominant contribution to the annihilation rate in the late Universe for dark matter masses below ∼ 1 TeV. Using a toy model of leptophilic dark matter, we calculate the annihilation cross-section into a lepton-antilepton pair with a Higgs boson and investigate the energy spectra of the final stable particles at the annihilation point.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Higgs vacuum stability and inflationary dynamics after BICEP2 and PLANCK dust polarisation data

If the recent detection of B-mode polarization of the Cosmic Microwave Background by BICEP2 observations, withstand the test of time after the release of recent PLANCK dust polarisation data, then it would surprisingly put the inflationary scale near Grand Unification scale if one considers single-field inflationary models. On the other hand, Large Hadron Collider has observed the elusive Higgs particle whose presently observed mass can lead to electroweak vacuum instability at high scale (∼ O(10{sup 10}) GeV). In this article, we seek for a simple particle physics model which can simultaneously keep the vacuum of the theory stable and yield high-scale inflation successfully. To serve our purpose, we extend the Standard Model of particle physics with a U(1){sub B-L} gauged symmetry which spontaneously breaks down just above the inflationary scale. Such a scenario provides a constrained parameter space where both the issues of vacuum stability and high-scale inflation can be successfully accommodated. The threshold effect on the Higgs quartic coupling due to the presence of the heavy inflaton field plays an important role in keeping the electroweak vacuum stable. Furthermore, this scenario is also capable of reheating the universe at the end of inflation. Though the issues of Dark Matter and Dark Energy, which dominate the late-time evolution of our universe, cannot be addressed within this framework, this model successfully describes the early universe dynamics according to the Big Bang model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Lattice calculation of the decay of primordial Higgs condensate

We study the resonant decay of the primordial Standard Model Higgs condensate after inflation into SU(2) gauge bosons on the lattice. We find that the non-Abelian interactions between the gauge bosons quickly extend the momentum distribution towards high values, efficiently destroying the condensate after the onset of backreaction. For the inflationary scale H = 10{sup 8} GeV, we find that 90% of the Higgs condensate has decayed after n∼ 10 oscillation cycles. This differs significantly from the Abelian case where, given the same coupling strengths, most of the condensate would persist after the resonance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Search for Higgs boson decays into a pair of pseudoscalar particles in the $bbμμ$ final state with the ATLAS detector in pp collisions at $\sqrt{s} =$ 13 TeV

This paper presents a search for decays of the Higgs boson with a mass of 125 GeV into a pair of new pseudoscalar particles, $H→aa$, where one a-boson decays into a b-quark pair and the other into a muon pair. The search uses 139 fb -1 of proton-proton collision data at a center-of-mass energy of $\sqrt{s} =$ 13 TeV recorded between 2015 and 2018 by the ATLAS experiment at the LHC. A narrow dimuon resonance is searched for in the invariant mass spectrum between 16 GeV and 62 GeV. The largest excess of events above the Standard Model backgrounds is observed at a dimuon invariant mass of 52 GeV and corresponds to a local (global) significance of 3.3σ (1.7σ). Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to the $bbμμ$ final state, $B(H→aa→bbμμ)$, and are in the range 0.2-4.0×10 -4 , depending on the signal mass hypothesis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Raising the Higgs mass with Yukawa couplings for isotriplets in vectorlike extensions of minimal supersymmetry

Extra vectorlike matter with both electroweak-singlet masses and large Yukawa couplings can significantly raise the lightest Higgs boson mass in supersymmetry through radiative corrections. I consider models of this type that involve a large Yukawa coupling between weak isotriplet and isodoublet chiral supermultiplets. The particle content can be completed to provide perturbative gauge coupling unification, in several different ways. The impact on precision electroweak observables is shown to be acceptably small, even if the new particles are as light as the current experimental bounds of order 100 GeV. I study the corrections to the lightest Higgs boson mass, and discuss the general features of the collider signatures for the new fermions in these models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Four generations, Higgs physics, and the MSSM

We consider the effects of a fourth generation of chiral fermions within the MSSM (minimal supersymmetric standard model). Such a model offers the possibility of having the lightest neutral Higgs boson significantly heavier than in the three generation MSSM. The model is highly constrained by precision electroweak data, along with Higgs searches at the Tevatron. In addition, the requirements of perturbative unitarity and direct searches for heavy quarks imply that the four generation MSSM is only consistent for tan{beta}{approx}1 and highly tuned 4th generation fermion masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Probing the light Higgs pole resonance annihilation of dark matter in the light of XENON100 and CDMS-II observations

We consider the prospect of lightest neutralino ({chi}-tilde{sub 1}{sup 0}) as a dark matter candidate in light of recent interesting observations from the XENON100 and CDMS-II experiments in minimal supergravity framework with large tan{beta} and nonvanishing A{sub 0}. Within the WMAP satisfied zone, there is a large direct detection reach of lighter {chi}-tilde{sub 1}{sup 0} in the lighter Higgs boson mediated resonance annihilation domain of the above scenario. It is seen that the heavier Higgs boson plays a dominating role in the {chi}-tilde{sub 1}{sup 0}-p cross section in the associated zone of parameter space in spite of having a larger mass. Possible LHC signatures are discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Semi-inclusive bottom-Higgs production at LHC: The complete one-loop electroweak effect in the MSSM

We present the first complete calculation of the one-loop electroweak effect in the process of semi-inclusive bottom-Higgs production at LHC in the minimal supersymmetric standard model. The size of the electroweak contribution depends on the choice of the final produced neutral Higgs boson and can be relevant, in some range of the input parameters. A comparison of the one-loop results obtained in two different renormalization schemes is also performed, showing a very good next-to-leading order scheme independence. We further comment on two possible, simpler, approximations of the full next-to-leading order result, and on their reliability.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

SU(4){sub L}xU(1){sub X} models with little Higgs mechanism

We study the aspects of the fermion and gauge boson sectors in SU(4){sub L}xU(1){sub X} models with a little Higgs mechanism. We introduce a new setup of fermions, which ensures the cancellation of gauge anomaly and the cancellation of one-loop quadratic divergence to the Higgs mass for all fermion multiplets and gauge bosons. We explicitly present the interactions between the standard model fermions and the heavy gauge bosons to discuss the phenomenological implications of extra Z{sup '} and Z{sup ''} gauge bosons based on recent experimental data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Massive gravity in de Sitter space via the gravitational Higgs mechanism

In this paper we discuss massive gravity in de Sitter space via the gravitational Higgs mechanism, which provides a nonlinear definition thereof. The Higgs scalars are described by a nonlinear sigma model, which includes higher derivative terms required to obtain the Fierz-Pauli mass term. Using the aforesaid nonperturbative definition, we address the appearance of an enhanced local symmetry and a null norm state in the linearized massive gravity in de Sitter space at the special value of the graviton mass to the Hubble parameter ratio. By studying full nonperturbative equations of motion, we argue that there is no enhanced symmetry in the full nonlinear theory. We then argue that in the full nonlinear theory no null norm state is expected to arise at the aforesaid special value. This suggests that no ghost might be present for lower graviton mass values and the full nonlinear theory might be unitary for all values of the graviton mass and the Hubble parameter with no van Dam-Veltman-Zakharov discontinuity. We argue that this is indeed the case by studying the full nonlinear Hamiltonian for the relevant conformal and helicity-0 longitudinal modes. In particular, we argue that no negative norm state is present in the full nonlinear theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗