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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
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DOE OSTI2012

Mixed sneutrino dark matter in light of the 2011 XENON and LHC results

In the context of supersymmetric models in which small Dirac neutrino masses are generated by supersymmetry breaking, a mainly right-handed (RH) mixed sneutrino can be an excellent cold dark matter (DM) candidate. We perform a global analysis of the Minimal Supersymmetric Standard Model (MSSM)+RH neutrino parameter space by means of Markov Chain Monte Carlo sampling. We include all relevant constraints from collider and dark matter searches, paying particular attention to nuclear and astrophysical uncertainties. Two distinct cases can satisfy all constraints: heavy sneutrino DM with mass of order 100 GeV, as well as light sneutrino DM with mass of about 3–6 GeV. We discuss the implications for direct and indirect dark matter searches, as well as for SUSY and Higgs searches at the LHC for both, the light and the heavy sneutrino dark matter case. The light sneutrino case is excluded by the 125–126 GeV Higgs signal.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Mixed inflaton and curvaton scenario with sneutrinos

A variation of sneutrino inflation based on χ{sup 2} potential is considered where the inflaton and the late-decaying field are sneutrinos of different generations. The lighter, late-decaying sneutrino dilutes the gravitinos over-produced after inflaton decay and generates the matter asymmetry. It can also significantly contribute to the curvature perturbation, realizing the mixed inflaton-curvaton case. The cosmic microwave background (CMB) observables can distinguish this case from inflation with χ{sup 2} potential, provided that the initial value of the late-decaying sneutrino is either an order of magnitude smaller or larger than the reduced Planck scale.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

PAMELA and FERMI limits on the neutralino-chargino mass degeneracy

Searches for Dark Matter (DM) particles with indirect detection techniques have reached important milestones with the precise measurements of the anti-proton ( p-bar ) and gamma-ray spectra, notably by the PAMELA and FERMI-LAT experiments. While the γ-ray results have been used to test the thermal Dark Matter hypothesis and constrain the Dark Matter annihilation cross section into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA experiment remains relatively unexploited. Here we show that the latter can be used to set a constraint on the neutralino-chargino mass difference. To illustrate our point we use a Supersymmetric model in which the gauginos are light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP) is the neutralino. In this framework the W{sup +}W{sup −} production is expected to be significant, thus leading to large p-bar and γ-ray fluxes. After determining a generic limit on the Dark Matter pair annihilation cross section into W{sup +}W{sup −} from the p-bar data only, we show that one can constrain scenarios in which the neutralino-chargino mass difference is as large as ≅ 20 GeV for a mixed neutralino (and intermediate choices of the p-bar propagation scheme). This result is consistent with the limit obtained by using the FERMI-LAT data. As a result, we can safely rule out the pure wino neutralino hypothesis if it is lighter than 450 GeV and constitutes all the Dark Matter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Axions and saxions from the primordial supersymmetric plasma and extra radiation signatures

We calculate the rate for thermal production of axions and saxions via scattering of quarks, gluons, squarks, and gluinos in the primordial supersymmetric plasma. Systematic field theoretical methods such as hard thermal loop resummation are applied to obtain a finite result in a gauge-invariant way that is consistent to leading order in the strong gauge coupling. We calculate the thermally produced yield and the decoupling temperature for both axions and saxions. For the generic case in which saxion decays into axions are possible, the emitted axions can constitute extra radiation already prior to big bang nucleosynthesis and well thereafter. We update associated limits imposed by recent studies of the primordial helium-4 abundance and by precision cosmology of the cosmic microwave background and large scale structure. We show that the trend towards extra radiation seen in those studies can be explained by late decays of thermal saxions into axions and that upcoming Planck results will probe supersymmetric axion models with unprecedented sensitivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Dark radiation constraints on mixed Axion/Neutralino dark matter

Recent analyses of CMB data combined with the measurement of BAO and H{sub 0} show that dark radiation — parametrized by the apparent number of additional neutrinos ΔN{sub eff} contributing to the cosmic expansion — is bounded from above by about ΔN{sub eff}∼<1.6 at 95% CL. We consider the mixed axion/neutralino cold dark matter scenario which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by hadronic axions with a concommitant axion(a)/saxion(s)/axino(ã) supermultiplet. Our new results include improved calculations of thermal axion and saxion production and include effects of saxion decay to axinos and axions. We show that the above bound on ΔN{sub eff} is easily satisfied if saxions are mainly thermally produced and m{sub LSP} < m{sub ã}∼<m{sub s}. However, if the dominant mechanism of saxion production is through coherent oscillations, the CMB data provides a strong bound on saxion production followed by saxion decays to axions. Furthermore we show that scenarios with mixed neutralino/axion dark matter are highly constrained by combined CMB, BBN and Xe-100 constraints. In particular, supersymmetric models with a standard overabundance of neutralino dark matter are excluded for all values of the Peccei-Quinn breaking scale. Next generation WIMP direct detection experiments may be able to discover or exclude mixed axion-neutralino CDM scenarios where s → aa is the dominant saxion decay mode.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Matter inflation with A{sub 4} flavour symmetry breaking

We discuss model building in tribrid inflation, which is a framework for realising inflation in the matter sector of supersymmetric particle physics models. The inflaton is a D-flat combination of matter fields, and inflation ends by a phase transition in which some Higgs field obtains a vacuum expectation value. We first describe the general procedure for implementing tribrid inflation in realistic models of particle physics that can be applied to a wide variety of BSM particle physics models around the GUT scale. We then demonstrate how the procedure works for an explicit lepton flavour model based on an A{sub 4} family symmetry. The model is both predictive and phenomenologically viable, and illustrates how tribrid inflation connects cosmological and particle physics parameters. In particular, it predicts a relation between the neutrino Yukawa coupling and the running of the spectral index α{sub s}. We also show how topological defects from the flavour symmetry breaking can be avoided automatically.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

On the sbottom resonance in dark matter scattering

A resonance in the neutralino-nucleus elastic scattering cross section is usually purported when the neutralino-sbottom mass difference m{sub b-tilde}−m{sub χ} is equal to the bottom quark mass m{sub b} ∼ 4 GeV. Such a scenario has been discussed as a viable model for light ( ∼ 10 GeV) neutralino dark matter as explanation of possible DAMA and CoGeNT direct detection signals. Here we give physical and analytical arguments showing that the sbottom resonance may actually not be there. In particular, we show analytically that the one-loop gluon-neutralino scattering amplitude has no pole at m{sub b-tilde} = m{sub χ}+m{sub b}, while by analytic continuation to the regime m{sub b-tilde} < m{sub χ}, it develops a pole at m{sub b-tilde} = m{sub χ}−m{sub b}. In the limit of vanishing gluon momenta, this pole corresponds to the only cut of the neutralino self-energy diagram with a quark and a squark running in the loop, when the decay process χ→ Q-tilde +Q becomes kinematically allowed. The pole can be interpreted as the formation of a b-tilde b-bar qqq or b-tilde *bqqq resonant state (where qqq are the nucleon valence quarks), which is however kinematically not accessible if the neutralino is the LSP. Our analysis shows that the common practice of estimating the neutralino-nucleon cross section by introducing an ad-hoc pole at m{sub b-tilde} = m{sub χ}+m{sub b} into the effective four-fermion interaction (also including higher-twist effects) should be discouraged, since it corresponds to adding a spurious pole to the scattering process at the center-of-mass energy (s){sup 1/2} ≅ m{sub χ} ≅ m{sub b-tilde}−m{sub b}. Our considerations can be extended from the specific case of supersymmetry to other similar cases in which the dark matter particle scatters off nucleons through the exchange of a b-flavored state almost degenerate in mass with the dark matter particle, such as for instance in theories with extra dimensions and in other mass-degenerate dark matter scenarios recently discussed in the literature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Enhanced lines and box-shaped features in the gamma-ray spectrum from annihilating dark matter in the NMSSM

We study spectral features in the gamma-ray emission from dark matter (DM) annihilation in the Next-to-Minimal Supersymmetric Standard Model (NMSSM), with either neutralino or right-handed (RH) sneutrino DM . We perform a series of scans over the NMSSM parameter space, compute the DM annihilation cross section into two photons and the contribution of box-shaped features, and compare them with the limits derived from the Fermi-LAT search for gamma-ray lines using the latest Pass 8 data. We implement the LHC bounds on the Higgs sector and on the masses of supersymmetric particles as well as the constraints on low-energy observables. We also consider the recent upper limits from the Fermi-LAT satellite on the continuum gamma-ray emission from dwarf spheroidal galaxies (dSphs). We show that in the case of the RH sneutrino the constraint on gamma-ray spectral features can be more stringent than the dSph bounds. This is due to the Breit-Wigner enhancement near the ubiquitous resonances with a CP even Higgs and the contribution of scalar and pseudoscalar Higgs final states to box-shaped features. By contrast, for neutralino DM, the di-photon final state is only enhanced in the resonance with a Z boson and box-shaped features are even more suppressed. Therefore, the observation of spectral features could constitute a discriminating factor between both models. In addition, we compare our results with direct DM searches, including the SuperCDMS and LUX limits on the elastic DM-nucleus scattering cross section and show that some of these scenarios would be accessible to next generation experiments. Thus, our findings strengthen the idea of complementarity among distinct DM search strategies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Cosmology with a heavy Polonyi field

We consider a cosmologically consistent scenario with a heavy Polonyi field. The Polonyi field with a mass of O(100) TeV decays before the Big-Bang Nucleosynthesis (BBN) and avoids the severe constraint from the BBN. However, the abundance of the Lightest Supersymmetric Particle (LSP) produced from the decay often exceeds the observed dark matter density. In our scenario, the dark matter density is obtained by the LSP abundance with an aid of entropy production, and baryon asymmetry is generated by the Affleck-Dine mechanism. We show that the observed baryon-to-dark matter ratio of O(0.1−1) is naturally explained in sequestering models with a QCD axion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Sneutrino Inflation with α-attractors

Sneutrino inflation employs the fermionic partners of the inflaton and stabilizer field as right-handed neutrinos to realize the seesaw mechanism for light neutrino masses. We show that one can improve the latest version of this scenario and its consistency with the Planck data by embedding it in the theory of cosmological α-attractors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Leptogenesis in B-L gauged supersymmetry with MSSM Higgs sector

We study a modified version of a U(1){sub B-L} gauged MSSM that was recently shown to produce a new source of leptogenesis through the CP asymmetry of sneutrinos and antisneutrinos [K. S. Babu, Yanzhi Meng, and Zurab Tavartkiladze, Phys. Lett. B 681, 37 (2009)]. By taking all superpotential terms and couplings between the MSSM Higgs and B-L scalar sectors into account we find that the model allows a large enough CP violation to explain the observed baryon number to entropy ratio. Monte Carlo analysis shows that a large amount of CP violation can be produced in the decays of the B-L Higgs bosons and that there are two dominating channels that drive CP violation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Yukawa coupling and anomalous magnetic moment of the muon: An update for the LHC era

We study the interplay between a soft muon Yukawa coupling generated radiatively with the trilinear A-terms of the minimal supersymmetric standard model (MSSM) and the anomalous magnetic moment of the muon. In the absence of a tree-level muon Yukawa coupling the lightest smuon mass is predicted to be in the range between 600 GeV and 2200 GeV at 2{sigma}, if the bino mass M{sub 1} is below 1 TeV. Therefore, a detection of a smuon (in conjunction with a sub-TeV bino) at the LHC would directly imply a nonzero muon Yukawa coupling in the MSSM superpotential. Inclusion of slepton flavor mixing could in principle lower the mass of one smuonlike slepton below 600 GeV. However, the experimental bounds on radiative lepton decays instead strengthen the lower mass bound, with larger effects for smaller M{sub 1}, We also extend the analysis to the electron case and find that a light selectron close to the current experimental search limit may prove the MSSM electron Yukawa coupling to be nonzero.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measuring a light neutralino mass at the ILC: Testing the MSSM neutralino cold dark matter model

The LEP experiments give a lower bound on the neutralino mass of about 46 GeV which, however, relies on a supersymmetric grand unification relation. Dropping this assumption, the experimental lower bound on the neutralino mass vanishes completely. Recent analyses suggest, however, that in the minimal supersymmetric standard model (MSSM), a light neutralino dark matter candidate has a lower bound on its mass of about 7 GeV. In light of this, we investigate the mass sensitivity at the ILC for very light neutralinos. We study slepton pair production, followed by the decay of the sleptons to a lepton and the lightest neutralino. We find that the mass measurement accuracy for a few-GeV neutralino is around 2 GeV, or even less if the relevant slepton is sufficiently light. We thus conclude that the ILC can help verify or falsify the MSSM neutralino cold dark matter model even for very light neutralinos.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Multiphoton signal in supersymmetry comprising nonpointing photon(s) at the LHC

We study a distinct supersymmetric signal of multiphotons in association with jets and missing transverse energy. At least one of these photons has the origin in displaced vertex, and thus it is delayed and nonpointing. We consider a supersymmetric scenario in which the gravitino is the lightest supersymmetric particle (LSP) (with a mass {approx}1 keV) and the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP). The NLSP decays dominantly into a photon and a gravitino within the detector with a decay length ranging from c{tau}{sub {tilde {chi}}} {approx}50-100 cm. In addition, we assume that the second-lightest neutralino and the lightest neutralino are nearly degenerate and this leads to a prompt radiative decay of the next-to-lightest neutralino into a photon and a lightest neutralino with a large branching ratio. Such degenerate neutralinos can be realized in various representations of the SU(5), SO(10) and E(6) GUT group. The nonpointing photons can be reconstructed at the electromagnetic calorimeter of the ATLAS detector, which have been designed with good timing and directional resolution. We find that with a center-of-mass energy E{sub cm}=14 TeV at an integrated luminosity of 100 fb{sup -1} one may see evidence of hundreds of triphoton events at the LHC, in addition to several thousands diphoton events. We also predict the event rates even at the early phase of LHC run.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Do new data on B{sup +{yields}{tau}+{nu}}{sub {tau}} decays point to an early discovery of supersymmetry at the LHC?

The recent Belle and BABAR measurements of the branching ratio of B{sup +{yields}{tau}+{nu}}{sub {tau}} indicate a significant deviation from the standard model prediction. We demonstrate that this measurement has a serious impact on models with minimal flavor violation involving a charged Higgs boson, ruling out a large portion of the currently allowed parameter space. In the constrained minimal supersymmetric standard model, this creates a tension between the measurements of B{sup +{yields}{tau}+{nu}}{sub {tau}} and the anomalous magnetic moment of the muon, unless tan{beta} is small, {mu}>0, and A{sub 0} takes a large negative value. In fact, a very small region of the parameter space of this model, with small values of m{sub 0} and m{sub 1/2}, survives all the constraints at 95% C.L. It is remarkable that this specific region is still consistent with the lightest supersymmetric particle as the dark matter. Moreover, it predicts observable supersymmetric signals in the early runs of the LHC, even perhaps at 7 TeV. We also show that a consistent explanation for the deviation of the B{sup +{yields}{tau}+{nu}}{sub {tau}} branching ratio from the standard model can be achieved in a nonuniversal Higgs-mass model, which could also predict early signals of supersymmetry at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Scalar neutrinos at the LHC

We study a softly broken supersymmetric model whose gauge symmetry is that of the standard model gauge group times an extra Abelian symmetry U(1){sup '}. We call this gauge-extended model the U(1){sup '} model, and we study a U(1){sup '} model with a secluded sector such that neutrinos acquire Dirac masses via higher-dimensional terms allowed by the U(1){sup '} invariance. In this model the {mu} term of the minimal supersymmetric model (MSSM) is dynamically induced by the vacuum expectation value of a singlet scalar. In addition, the model contains exotic particles necessary for anomaly cancellation, and extra singlet bosons for achieving correct Z{sup '}/Z mass hierarchy. The neutrinos are charged under U(1){sup '}, and thus, their production and decay channels differ from those in the MSSM in strength and topology. We implement the model into standard packages and perform a detailed analysis of sneutrino production and decay at the Large Hadron Collider, for various mass scenarios, concentrating on three types of signals: (1) 0l+MET, (2) 2l+MET, and (3) 4l+MET. We compare the results with those of the MSSM whenever possible, and analyze the standard model background for each signal. The sneutrino production and decays provide clear signatures enabling distinction of the U(1){sup '} model from the MSSM at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Determining the squark mass at the LHC

We propose a new way to determine the squark mass based on the shape of dijet invariant mass distribution of supersymmetry dijet events at the Large Hadron Collider. Our algorithm, which is based on event kinematics, requires that the branching ratio B(q-tilde{yields}qZ-tilde{sub 1}) is substantial for at least some types of squarks, and that m{sub Z}-tilde{sub 1}{sup 2}/m{sub q}-tilde{sup 2}<<1. We select dijet events with no isolated leptons, and impose cuts on the total jet transverse energy, E{sub T}{sup tot}=E{sub T}(j{sub 1})+E{sub T}(j{sub 2}), on {alpha}=E{sub T}(j{sub 2})/m{sub jj}, and on the azimuthal angle between the two jets to reduce standard model backgrounds. The shape of the resulting dijet mass distribution depends sensitively on the squark mass, especially if the integrated luminosity is sufficient to allow a hard enough cut on E{sub T}{sup tot} and yet leave a large enough signal to obtain the m{sub jj} distribution. We simulate the signal and standard model backgrounds for 100 fb{sup -1} integrated luminosity at 14 TeV requiring E{sub T}{sup tot}>700 GeV. We show that it should be possible to extract m{sub q}-tilde to within about 3% at 95% confidence level-similar to the precision obtained using m{sub T2}-from the dijet mass distribution if m{sub q}-tilde{approx}650 GeV, or to within {approx}5% if m{sub q}-tilde{approx}1 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗