arXiv subjects

Gabe Shaughnessy

Publications and source records attributed to Gabe Shaughnessy.

50 records · Page 3Linked to original sources

arXiv2008

Spin Dependence of Dark Matter Scattering

New experiments designed to discover a weakly interacting dark matter (DM) particle via spin dependent scattering can distinguish models of electroweak symmetry breaking. The plane of spin dependent versus spin independent DM scattering cross sections is a powerful model diagnostic. We detail representative predictions of mSUGRA, singlet extended SM and MSSM, a new Dirac neutrino, Littlest Higgs with T-parity (LHT) and Minimal Universal Extra Dimensions (mUED) models. Of these models, the nMSSM has the largest spin dependent (SD) cross section. It has a very light neutralino which would give lower energy nuclear recoils. The Focus Point region of mSUGRA, mUED and the right handed neutrino also predict a very large SD cross section and predict a large signal of high energy neutrinos in the IceCube experiment from annihilations of dark matter in the Sun. We also describe a model independent treatment of the scattering of DM particles of different intrinsic spins.

hep-ph↗

arXiv2007

Monochromatic Neutrino Signals from Dark Matter Annihilation

Dark matter annihilations in the Sun to neutrino-antineutrino pairs have striking signatures in neutrino detectors such as IceCube and KM3. We make a model independent study of the signals after propagation of the neutrinos from the center of the Sun to the Earth. A large spin-dependent DM capture cross section in the Sun make the discovery prospects robust.

astro-ph↗

arXiv2007

High energy neutrinos from neutralino annihilations in the Sun

Neutralino annihilations in the Sun to weak boson and top quark pairs lead to high-energy neutrinos that can be detected by the IceCube and KM3 experiments in the search for neutralino dark matter. We calculate the neutrino signals from real and virtual WW, ZZ, Zh, and $t \bar t$ production and decays, accounting for the spin-dependences of the matrix elements, which can have important influences on the neutrino energy spectra. We take into account neutrino propagation including neutrino oscillations, matter-resonance, absorption, and nu_tau regeneration effects in the Sun and evaluate the neutrino flux at the Earth. We concentrate on the compelling Focus Point (FP) region of the supergravity model that reproduces the observed dark matter relic density. For the FP region, the lightest neutralino has a large bino-higgsino mixture that leads to a high neutrino flux and the spin-dependent neutralino capture rate in the Sun is enhanced by 10^3 over the spin-independent rate. For the standard estimate of neutralino captures, the muon signal rates in IceCube are identifiable over the atmospheric neutrino background for neutralino masses above M_Z up to 400 GeV.

hep-ph↗

arXiv2007

Singlet Higgs Phenomenology and the Electroweak Phase Transition

We study the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. We determine the conditions on the scalar potential parameters that lead to a strong first order phase transition as needed to produce the observed baryon asymmetry of the universe. We analyze the constraints on the potential parameters derived from Higgs boson searches at LEP and electroweak precision observables. For models that satisfy these constraints and that produce a strong first order phase transition, we discuss the prospective signatures in future Higgs studies at the Large Hadron Collider and a Linear Collider. We argue that such studies will provide powerful probes of phase transition dynamics in models with an extended scalar sector.

hep-ph↗

arXiv2007

LHC Phenomenology of an Extended Standard Model with a Real Scalar Singlet

Gauge singlet extensions of the Standard Model (SM) scalar sector may help remedy its theoretical and phenomenological shortcomings while solving outstanding problems in cosmology. Depending on the symmetries of the scalar potential, such extensions may provide a viable candidate for the observed relic density of cold dark matter or a strong first order electroweak phase transition needed for electroweak baryogenesis. Using the simplest extension of the SM scalar sector with one real singlet field, we analyze the generic implications of a singlet-extended scalar sector for Higgs boson phenomenology at the Large Hadron Collider (LHC). We consider two broad scenarios: one in which the neutral SM Higgs and singlet mix and the other in which no mixing occurs and the singlet can be a dark matter particle. For the first scenario, we analyze constraints from electroweak precision observables and their implications for LHC Higgs phenomenology. For models in which the singlet is stable, we determine the conditions under which it can yield the observed relic density, compute the cross sections for direct detection in recoil experiments, and discuss the corresponding signatures at the LHC.

hep-ph↗

arXiv2007

Precision gluino mass at the LHC in SUSY models with decoupled scalars

One way to ameliorate the SUSY flavor and CP problems is to postulate that scalar masses lie in the TeV or beyond regime. For example, the focus point (FP) region of the minimal supergravity (mSUGRA) model is especially compelling in that heavy scalar masses can co-exist with low fine-tuning while yielding the required relic abundance of cold dark matter (via a mixed higgsino-bino neutralino). We examine many of the characteristics of collider events expected to arise at the CERN LHC in models with multi-TeV scalars, taking the mSUGRA FP region as a case study. The collider events are characterized by a hard component arising from gluino pair production, plus a soft component arising from direct chargino and neutralino production. Gluino decays in the FP region are characterized by lengthy cascades yielding very large jet and lepton multiplicities, and a large b-jet multiplicity. Thus, as one steps to higher jet, b-jet or lepton multiplicity, signal-over-background rates should steadily improve. The lengthy cascade decays make mass reconstruction via kinematic edges difficult; however, since the hard component is nearly pure gluino pair production, the gluino mass can be extracted to +- 8% via total rate for \eslt +\ge 7-jet +\ge 2 b-jet events, assuming 100 fb^{-1} of integrated luminosity. The distribution of invariant mass of opposite-sign/same-flavor dileptons in the hard component exhibits two dilepton mass edges: m_{\tz_2}-m_{\tz_1} and m_{\tz_3}-m_{\tz_1}. As a consistency check, the same mass edges should be seen in isolated opposite-sign dileptons occurring in the soft component trilepton signal which originates mainly from chargino-neutralino production.

hep-ph↗

arXiv2007

Recoil Detection of the Lightest Neutralino in MSSM Singlet Extensions

We investigate the correlated predictions of singlet extended MSSM models for direct detection of the lightest neutralino with its cosmological relic density. To illustrate the general effects of the singlet, we take heavy sleptons and squarks. We apply LEP, $(g-2)_μ$ and perturbativity constraints. We find that the WMAP upper bound on the cold dark matter density limits much of the parameter space to regions where the lightest neutralino can be discovered in recoil experiments. The results for the NMSSM and UMSSM are typically similar to the MSSM since their light neutralinos have similar compositions and masses. In the n/sMSSM the neutralino is often very light and its recoil detection is within the reach of the CDMS II experiment. In general, most points in the parameter spaces of the singlet models we consider are accessible to the WARP experiment.

hep-ph↗

arXiv2007

TeV physics and the Planck scale

Supersymmetry is one of the best motivated possibilities for new physics at the TeV scale. However, both concrete string constructions and phenomenological considerations suggest the possibility that the physics at the TeV scale could be more complicated than the Minimal Supersymmetric Standard Model (MSSM), e.g., due to extended gauge symmetries, new vector-like supermultiplets with non-standard SU(2)xU(1) assignments, and extended Higgs sectors. We briefly comment on some of these possibilities, and discuss in more detail the class of extensions of the MSSM involving an additional standard model singlet field. The latter provides a solution to the $μ$ problem, and allows significant modifications of the MSSM in the Higgs and neutralino sectors, with important consequences for collider physics, cold dark matter, and electroweak baryogenesis.

hep-ph↗

arXiv2006

Collider Signatures of Singlet Extended Higgs Sectors

We explore the collider signatures of the Higgs sectors in singlet-extended MSSM models. We find that even with reduced couplings due to singlet mixing, a significant portion of the parameter spaces have a discoverable Higgs via traditional decay modes or via invisible decays (directly to neutralinos or through cascade decays to neutralinos and neutrinos). For illustrative points in parameter space we give the likelihood of Higgs discovery. In cases where neither traditional nor invisible modes can discover the Higgs, the neutralino sector may provide evidence for the extended models.

hep-ph↗

arXiv2006

Neutralino Signatures of the Singlet Extended MSSM

Extending the Higgs sector of the MSSM by the addition of a gauge singlet scalar field can remedy the mu problem. We explore the implications of extended models for both the spectrum of the neutralinos and the cascade decays of the neutralinos and charginos. Extra steps due to light decoupled neutralinos in the cascade decays of both neutralinos and charginos allow an excess of trilepton events compared to the MSSM and the existence of events with higher lepton multiplicity. Additionally, displaced vertices of the chi_2^0 due to small decay widths in some models may be observable.

hep-ph↗

arXiv2006

Singlet Extensions of the MSSM

The Higgs sector of the MSSM may be extended to solve the mu problem by the addition of a gauge singlet scalar field. We consider the consequences of the singlet on the Higgs and neutralino states compositions. We discuss the potential for discovering Higgs bosons of singlet models and observing the unique multilepton signatures of the extended neutralino sector.

hep-ph↗

arXiv2006

Neutralino annihilation to q qbar g

We compute the cross section for chi chi -> q qbar g at order alpha_s^2/M_{squark}^6 arising from interference between the tree-level and loop-induced processes. This interference term is the same order in alpha_s as chi chi -> gg; for mass degenerate squarks M_{squark_R} = M_{squark_L} = M_{squark} we find v_{rel} sigma_{int} = [-2 m_{chi}^2 / 3 M_{squark}^2] v_{rel} sigma(chi chi -> gg).

hep-ph↗

arXiv2006

Higgs Sector in Extensions of the MSSM

Extensions of the Minimal Supersymmetric Standard Model (MSSM) with additional singlet scalar fields solve the important mu-parameter fine tuning problem of the MSSM. We compute and compare the neutral Higgs boson mass spectra, including one-loop corrections, of the following MSSM extensions: Next-to-Minimal Supersymmetric Standard Model (NMSSM), the nearly-Minimal Supersymmetric Standard Model (nMSSM), and the U(1)'-extended Minimal Supersymmetric Standard Model (UMSSM) by performing scans over model parameters. We find that the Secluded U(1)'-extended Minimal Supersymmetric Standard Model (sMSSM) is identical to the nMSSM if three of the additional scalars decouple. The dominant part of the one-loop corrections are model-independent since the singlet field does not couple to MSSM particles other than the Higgs doublets. Thus, model-dependent parameters enter the masses only at tree-level. We apply constraints from LEP bounds on the Standard Model and MSSM Higgs boson masses and the MSSM chargino mass, the invisible Z decay width, and the Z-Z' mixing angle. Some extended models permit a Higgs boson with mass substantially below the SM LEP limit or above theoretical limits in the MSSM. Ways to differentiate the models via masses, couplings, decays and production of the Higgs bosons are discussed.

hep-ph↗

arXiv2005

Neutralino annihilation beyond leading order

High-precision measurements of the relic dark matter density and the calculation of dark matter annihilation branching fractions in the sun or the galactic halo today motivate the computation of the neutralino annihilation cross section beyond leading order. We consider neutralino annihilation via squark exchange and parameterize the effective annihilation vertex as a dimension-six operator suppressed by two powers of the squark mass and related to the divergence of the axial vector current of the final-state quarks. Since the axial vector current is conserved at tree level in the limit of massless quarks, this dimension-six operator contains a suppression by the quark mass. The quark mass suppression can be lifted in two ways: (1) by corrections to the dimension-six operator involving the anomalous triangle diagram, and (2) by going to dimension-eight. We address the first of these possibilities by evaluating the anomalous triangle diagram, which contributes to neutralino annihilation to gluon pairs. We relate the triangle diagram via the anomaly equation to the decay of a pseudoscalar into two gluons and use the Adler-Bardeen theorem to extract the next-to-leading order (NLO) QCD corrections to chi chi --> gg from the known corrections to pseudoscalar decay. The strong dependence of the dominant chi chi --> q qbar cross section on the relative velocity of the neutralinos makes these NLO corrections unimportant at chi decoupling but significant today.

hep-ph↗