arXiv subjects

Pearl Sandick

Publications and source records attributed to Pearl Sandick.

67 records · Page 4Linked to original sources

arXiv2010

Signatures of Dark Star Remnants in the Galactic Halo

The very first stars likely formed from metal-free, molecular hydrogen-cooled gas at the centers of dark matter minihalos. Prior to nuclear fusion, these stars may have been supported by dark matter heating from annihilations in the star, in which case they could have grown to be quite massive before collapsing to black holes. Many remnant black holes and their surrounding dark matter density spikes may be part of our Milky Way halo today. Here we explore the gamma-ray signatures of dark matter annihilations in the dark matter spikes surrounding these black holes for a range of star formation scenarios, black hole masses, and dark matter annihilation modes. Data from the Fermi Gamma-Ray Space Telescope are used to constrain models of dark matter annihilation and the formation of the first stars.

astro-ph.CO↗

arXiv2010

The Sensitivity of the IceCube Neutrino Detector to Dark Matter Annihilating in Dwarf Galaxies

In this paper, we compare the relative sensitivities of gamma-ray and neutrino observations to the dark matter annihilation cross section in leptophilic models such as have been designed to explain PAMELA data. We investigate whether the high energy neutrino telescope IceCube will be competitive with current and upcoming searches by gamma-ray telescopes, such as the Atmospheric Cerenkov Telescopes (ACTs) (HESS, VERITAS and MAGIC), or the Fermi Gamma Ray Space Telescope, in detecting or constraining dark matter particles annihilating in dwarf spheroidal galaxies. We find that after ten years of observation of the most promising nearby dwarfs, IceCube will have sensitivity comparable to the current sensitivity of gamma-ray telescopes only for very heavy (m_X > 7 TeV) or relatively light (m_X < 200 GeV) dark matter particles which annihilate primarily to mu+mu-. If dark matter particles annihilate primarily to tau+tau-, IceCube will have superior sensitivity only for dark matter particle masses below the 200 GeV threshold of current ACTs. If dark matter annihilations proceed directly to neutrino-antineutrino pairs a substantial fraction of the time, IceCube will be competitive with gamma-ray telescopes for a much wider range of dark matter masses.

astro-ph.CO↗

arXiv2010

Particle Dark Matter: Status and Searches

A brief overview is given of the phenomenology of particle dark matter and the properties of some of the most widely studied dark matter candidates. Recent developments in direct and indirect dark matter searches are discussed.

astro-ph.CO↗

arXiv2009

Neutralino Dark Matter in MSSM Models with Non-Universal Higgs Masses

We consider the Minimal Supersymmetric Standard Model (MSSM) with varying amounts of non-universality in the soft supersymmetry-breaking contributions to the Higgs scalar masses. In addition to the constrained MSSM (CMSSM) in which these are universal with the soft supersymmetry-breaking contributions to the squark and slepton masses at the input GUT scale, we consider scenarios in which both the Higgs masses are non-universal by the same amount (NUHM1), and scenarios in which they are independently non-universal (NUHM2). As the lightest neutralino is a dark matter candidate, we demand that the relic density of neutralinos not be in conflict with measurements by WMAP and others, and examine the viable regions of parameter space. Prospects for direct detection of neutralino dark matter via elastic scattering in these scenarios are discussed.

hep-ph↗

arXiv2009

Update on the Direct Detection of Dark Matter in MSSM Models with Non-Universal Higgs Masses

We discuss the possibilities for the direct detection of neutralino dark matter via elastic scattering in variants of the minimal supersymmetric extension of the Standard Model (MSSM) with non-universal supersymmetry-breaking contributions to the Higgs masses, which may be either equal (NUHM1) or independent (NUHM2). We compare the ranges found in the NUHM1 and NUHM2 with that found in the MSSM with universal supersymmetry-breaking contributions to all scalar masses, the CMSSM. We find that both the NUHM1 and NUHM2 offer the possibility of larger spin-independent dark matter scattering cross sections than in the CMSSM for larger neutralino masses, since they allow the density of heavier neutralinos with large Higgsino components to fall within the allowed range by astrophysics. The NUHM1 and NUHM2 also offer more possibilities than the CMSSM for small cross sections for lower neutralino masses, since they may be suppressed by scalar and pseudoscalar Higgs masses that are larger than in the CMSSM.

hep-ph↗

arXiv2008

Varying the Universality of Supersymmetry-Breaking Contributions to MSSM Higgs Boson Masses

We consider the minimal supersymmetric extension of the Standard Model (MSSM) with varying amounts of non-universality in the soft supersymmetry-breaking contributions to the Higgs scalar masses. In addition to the constrained MSSM (CMSSM) in which these are universal with the soft supersymmetry-breaking contributions to the squark and slepton masses at the input GUT scale, we consider scenarios in which both the Higgs scalar masses are non-universal by the same amount (NUHM1), and scenarios in which they are independently non-universal (NUHM2). We show how the NUHM1 scenarios generalize the (m_{1/2}, m_0) planes of the CMSSM by allowing either mu or m_A to take different (fixed) values and we also show how the NUHM1 scenarios are embedded as special cases of the more general NUHM2 scenarios. Generalizing from the CMSSM, we find regions of the NUHM1 parameter space that are excluded because the LSP is a selectron. We also find new regions where the neutralino relic density falls within the range preferred by astrophysical and cosmological measurements, thanks to rapid annihilation through direct-channel Higgs poles, or coannihilation with selectrons, or because the LSP composition crosses over from being mainly bino to mainly Higgsino. Generalizing further to the NUHM2, we find regions of its parameter space where a sneutrino is the LSP, and others where neutralino coannihilation with sneutrinos is important for the relic density. In both the NUHM1 and the NUHM2, there are slivers of parameter space where the LHC has fewer prospects for discovering sparticles than in the CMSSM, because either m_{1/2} and/or m_0 may be considerably larger than in the CMSSM.

hep-ph↗

arXiv2008

Sparticle Discovery Potentials in the CMSSM and GUT-less Supersymmetry-Breaking Scenarios

We consider the potentials of the LHC and a linear e^+e^- collider (LC) for discovering supersymmetric particles in variants of the MSSM with soft supersymmetry-breaking mass parameters constrained to be universal at the GUT scale (CMSSM) or at some lower scale M_{in} (GUT-less models), as may occur in some scenarios with mirage unification. Whereas the LHC should be able to discover squarks and/or gluinos along all the CMSSM coannihilation strip where the relic neutralino LSP density lies within the range favoured for cold dark matter, many GUT-less models could escape LHC detection. In particular, if M_{in} < 10^{11} GeV, the LHC would not detect sparticles if the relic density lies within the favoured range. For any given discovery of supersymmetry at the LHC, in such GUT-less models the lightest neutralino mass and hence the threshold for sparticle pair production at a LC increases as M_{in} decreases, and the CMSSM offers the best prospects for measuring sparticles at a LC. For example, if the LHC discovers sparticles with 1 fb^{-1} of data, within the CMSSM a centre-of-mass energy of 600 GeV would suffice for a LC to to produce pairs of neutralinos, if they provide the cold dark matter, whereas over 1 TeV might be required in a general GUT-less model. These required energies increase to 800 GeV in the CMSSM and 1.4 TeV in GUT-less models if the LHC requires 10 fb^{-1} to discover supersymmetry.

hep-ph↗

arXiv2007

Dark Matter Phenomenology of GUT-less SUSY Breaking

We study models in which supersymmetry breaking appears at an intermediate scale, M_in, below the GUT scale. That is, that the soft supersymmetry-breaking parameters of the MSSM are universal at M_in. We demand that the lightest neutralino be the LSP, and that the relic neutralino density not conflict with measurements by WMAP and others, and study the morphology of this constraint as the universality scale is reduced from the GUT scale. At moderate values of M_in, we find that the allowed regions of the (m_1/2,m_0) plane are squeezed by the requirements of electroweak symmetry breaking and that the lightest neutralino be the LSP, whereas the constraint on the relic density is less severe. At very low M_in, the electroweak vacuum conditions become the dominant constraint, and a secondary source of astrophysical cold dark matter would be necessary to explain the measured relic density for nearly all values of the soft SUSY-breaking parameters and tan(beta).

hep-ph↗

arXiv2007

Phenomenology of GUT-less Supersymmetry Breaking

We study models in which supersymmetry breaking appears at an intermediate scale, M_{in}, below the GUT scale. We assume that the soft supersymmetry-breaking parameters of the MSSM are universal at M_{in}, and analyze the morphology of the constraints from cosmology and collider experiments on the allowed regions of parameter space as M_{in} is reduced from the GUT scale. We present separate analyses of the (m_{1/2},m_0) planes for tan(beta)=10 and tan(beta)=50, as well as a discussion of non-zero trilinear couplings, A_0. Specific scenarios where the gaugino and scalar masses appear to be universal below the GUT scale have been found in mirage-mediation models, which we also address here. We demand that the lightest neutralino be the LSP, and that the relic neutralino density not conflict with measurements by WMAP and other observations. At moderate values of M_{in}, we find that the allowed regions of the (m_{1/2},m_0) plane are squeezed by the requirements of electroweak symmetry breaking and that the lightest neutralino be the LSP, whereas the constraint on the relic density is less severe. At very low M_{in}, the electroweak vacuum conditions become the dominant constraint, and a secondary source of astrophysical cold dark matter would be necessary to explain the measured relic density for nearly all values of the soft SUSY-breaking parameters and tan(beta). We calculate the neutralino-nucleon cross sections for viable scenarios and compare them with the present and projected limits from direct dark matter searches.

hep-ph↗

arXiv2006

What if supersymmetry breaking appears below the GUT scale?

We consider the possibility that the soft supersymmetry-breaking parameters m_{1/2} and m_0 of the MSSM are universal at some scale M_{in} below the supersymmetric grand unification scale M_{GUT}, as might occur in scenarios where either the primordial supersymmetry-breaking mechanism or its communication to the observable sector involve a dynamical scale below M_{GUT}. We analyze the (m_{1/2}, m_0) planes of such sub-GUT CMSSM models, noting the dependences of phenomenological, experimental and cosmological constraints on M_{in}. In particular, we find that the coannihilation, focus-point and rapid-annihilation funnel regions of the GUT-scale CMSSM approach and merge when M_{in} \sim 10^{12} GeV. We discuss sparticle spectra and the possible sensitivity of LHC measurements to the value of M_{in}.

hep-ph↗

arXiv2006

Gravitational Waves from the First Stars

We consider the stochastic background of gravitational waves produced by an early generation of Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift $z \la 6$, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at $z\sim 10-20$ as indicated by the first year results released by WMAP. We find that the normal mode of star formation produces a gravitational wave background which peaks at 300-500 Hz and is within LIGO III sensitivity. The Population III component peaks at lower frequencies (30-100 Hz depending on the model), and could be detected by LIGO III as well as the planned BBO and DECIGO interferometers.

astro-ph↗

arXiv2006

The Relic Neutrino Backround from the First Stars

We consider the relic neutrino background produced by Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z \la 6, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at z ~ 10-20. We consider both a burst and non-burst model for Population III star formation. We find that although the high redshift burst of Population III stars does lead to an appreciable flux of neutrinos at relatively low energy (E_ν\approx 1 MeV), the observable neutrino flux is dominated by the normal mode of star formation. We also find that predicted fluxes are at the present level of the SuperK limit. As a consequence, the supernova relic neutrino background has a direct impact on models of chemical evolution and/or supernova dynamics.

astro-ph↗

arXiv2005

Neutrino Signatures from the First Stars

Evidence from the WMAP polarization data indicates that the Universe may have been reionized at very high redshift. It is often suggested that the ionizing UV flux originates from an early population of massive or very massive stars. Depending on their mass, such stars can explode either as type II supernovae or pair-instability supernovae, or may entirely collapse into a black hole. The resulting neutrino emission can be quite different in each case. We consider here the relic neutrino background produced by an early burst of Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z \la 6, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at z \sim 10-20. We find that although the high redshift burst of Population III stars does lead to an appreciable flux of neutrinos at relatively low energy (E_ν\approx 1 MeV), the observable neutrino flux is dominated by the normal mode of star formation. We also find that predicted fluxes are at the present level of the SuperK limit. As a consequence, the supernova relic neutrino background has a direct impact on models of chemical evolution and/or supernova dynamics.

astro-ph↗