arXiv subjects

Pearl Sandick

Publications and source records attributed to Pearl Sandick.

At least 55 records · Page 3Linked to original sources

arXiv2017

Black Holes, Dark Matter Spikes, and Constraints on Simplified Models with $t$-Channel Mediators

The density spike of dark matter (DM) in the subparsec region near the supermassive black hole at the Galactic Center can provide potentially observable gamma-ray signals coming from DM annihilations. Taking Fermi-$LAT$ data for the gamma-ray flux from the point source 3FGL J1745.6-2859c (Sgr A*), we calculate the resulting constraints on generic models of DM, allowing for the possibility of a non-negligible velocity-dependent component of the annihilation cross section. We consider a variety of selections for the astrophysical parameters that describe the spike profile and find that the gamma-ray flux is strongly dependent on these selections, particularly the modelling of spike depletion effects due to gravitational interactions with baryons, which affect the spike radius and steepness profile. We calculate constraints on the DM parameter space for both attenuated and idealized spikes, considering different choices for the steepness profiles in each case. We find that for the most conservative selection of parameters, corresponding to a depleted spike with an NFW cusp profile, the gamma-ray flux for a 100 GeV thermal relic is lower than current observational constraints by several orders of magnitude. For more optimistic choices of parameters corresponding to spikes that have not been attenuated, bounds on DM masses can be obtained for a variety of choices of steepness profiles. We then specialize to a class of simplified models of fermionic DM that annihilate dominantly through the $t-$channel exchange of two scalar mediators with arbitrary mixing angle $α$, and calculate the indirect detection constraints coming from the DM spike. Along the way, we discuss constraints on the astrophysical parameters describing the DM spike, taking the Galactic Center excess as a signal of DM annihilation.

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arXiv2016

Simplified Dark Matter Models with Charged Mediators: Prospects for Direct Detection

We consider direct detection prospects for a class of simplified models of fermionic dark matter (DM) coupled to left and right-handed Standard Model fermions via two charged scalar mediators with arbitrary mixing angle $α$. DM interactions with the nucleus are mediated by higher electromagnetic moments, which, for Majorana DM, is the anapole moment. After giving a full analytic calculation of the anapole moment, including its $α$ dependence, and matching with limits in the literature, we compute the DM-nucleon scattering cross-section and show the LUX and future LZ constraints on the parameter space of these models. We then compare these results with constraints coming from $Fermi$-LAT continuum and line searches. Results in the supersymmetric limit of these simplified models are provided in all cases. We find that future direct detection experiments will be able to probe most of the parameter space of these models for $\mathcal{O}(100-200)$ GeV DM and lightest mediator mass $\lesssim \mathcal{O}(5\%)$ larger than the DM mass. The direct detection prospects dwindle for larger DM mass and larger mass gap between the DM and the lightest mediator mass, although appreciable regions are still probed for $\mathcal{O}(200)$ GeV DM and lightest mediator mass $\lesssim \mathcal{O}(20\%)$ larger than the DM mass. The direct detection bounds are also attenuated near certain "blind spots" in the parameter space, where the anapole moment is severely suppressed due to cancellation of different terms. We carefully study these blind spots and the associated $Fermi$-LAT signals in these regions.

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arXiv2016

Gamma-ray Signals from Dark Matter Annihilation Via Charged Mediators

We consider a simplified model in which Majorana fermion dark matter annihilates to charged fermions through exchange of charged mediators. We consider the gamma-ray signals arising from the processes $XX \rightarrow \bar f f γ$, $γγ$, and $γZ$ in the most general case, including non-trivial fermion mass and non-trivial left-right mixing and $CP$-violating phase for the charged mediators. In particular, we find the most general spectrum for internal bremsstrahlung, which interpolates between the regimes dominated by virtual internal bremsstrahlung and by final state radiation. We also examine the variation in the ratio $σ(γγ) / σ(γZ)$ and the helicity asymmetry in the $XX \rightarrow γγ$ process, each as a function of mixing angle and $CP$-violating phase. As an application, we apply these results to searches for a class of MSSM models.

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arXiv2016

SUSY Dark Matter: Beyond the Standard Paradigm

Within the framework of the Minimal Supersymmetric Standard Model (MSSM), we explore a decoupling of the parameters into separate sectors that determine consistency with collider data, the abundance of dark matter, and potential signatures at direct dark matter searches. We consider weak-scale bino-like neutralino dark matter, and find that annihilations via light slepton exchange present a viable mechanism for obtaining the appropriate dark matter abundance assuming a thermal history. Constraints and prospects for discovery of these models are discussed, including the possibility that direct dark matter searches may be sensitive to these models if light squarks exhibit left-right mixing. Differences between the scenarios presented here and the typical expectations for the MSSM are discussed.

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arXiv2015

Beyond the CMSSM without an Accelerator: Proton Decay and Direct Dark Matter Detection

We consider two potential non-accelerator signatures of generalizations of the well-studied constrained minimal supersymmetric standard model (CMSSM). In one generalization, the universality constraints on soft supersymmetry-breaking parameters are applied at some input scale $M_{in}$ below the grand unification (GUT) scale $M_{GUT}$, a scenario referred to as `sub-GUT'. The other generalization we consider is to retain GUT-scale universality for the squark and slepton masses, but to relax universality for the soft supersymmetry-breaking contributions to the masses of the Higgs doublets. As with other CMSSM-like models, the measured Higgs mass requires supersymmetric particle masses near or beyond the TeV scale. Because of these rather heavy sparticle masses, the embedding of these CMSSM-like models in a minimal SU(5) model of grand unification can yield a proton lifetime consistent with current experimental limits, and may be accessible in existing and future proton decay experiments. Another possible signature of these CMSSM-like models is direct detection of supersymmetric dark matter. The direct dark matter scattering rate is typically below the reach of the LUX-ZEPLIN (LZ) experiment if $M_{in}$ is close to $M_{GUT}$, but may lie within its reach if $M_{in} \lesssim 10^{11}$ GeV. Likewise, generalizing the CMSSM to allow non-universal supersymmetry-breaking contributions to the Higgs offers extensive possibilities for models within reach of the LZ experiment that have long proton lifetimes.

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arXiv2015

Charged mediators in dark matter scattering with nuclei and the strangeness content of nucleons: Strange Brew

We consider a scenario, within the framework of the MSSM, in which dark matter is bino-like and dark matter-nucleon spin-independent scattering occurs via the exchange of light squarks which exhibit left-right mixing. We show that direct detection experiments such as LUX and SuperCDMS will be sensitive to a wide class of such models through spin-independent scattering. Moreover, these models exhibit properties, such as isospin violation, that are not typically observed for the MSSM LSP if scattering occurs primarily through Higgs exchange. The dominant nuclear physics uncertainty is the quark content of the nucleon, particularly the strangeness content.

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arXiv2015

Searching for Dark Matter Annihilation to Monoenergetic Neutrinos with Liquid Scintillation Detectors

We consider searches for dark matter annihilation to monoenergetic neutrinos in the core of the Sun. We find that liquid scintillation neutrino detectors have enhanced sensitivity to this class of dark matter models, due to the energy and angular resolution possible for electron neutrinos and antineutrinos that scatter via charged-current interactions. In particular we find that KamLAND, utilizing existing data, could provide better sensitivity to such models than any current direct detection experiment for $m_X \lesssim 15$ GeV. KamLAND's sensitivity is signal-limited, and future liquid scintillation or liquid argon detectors with similar energy and angular resolution, but with larger exposure, will provide significantly better sensitivity. These detectors may be particularly powerful probes of dark matter with mass $\mathcal{O}(10)$ GeV.

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arXiv2013

Lowering the Threshold in the DAMA Dark Matter Search

The DAMA experiment searches for Weakly Interacting Massive Particle (WIMP) dark matter via its expected but rare interactions within the detector, where the interaction rates will modulate throughout the year due to the orbital motion of the Earth. Over the course of more than 10 years of operation, DAMA has indeed detected a strong modulation in the event rate above the detector threshold of 2 keVee. Under standard assumptions regarding the dark matter halo and WIMP interactions, this signal is consistent with that expected of WIMPs of two different approximate masses: ~ 10 GeV and ~ 70 GeV. We examine how a lower threshold, allowed by recent upgrades to the DAMA detector, may shed light on this situation. We find that the lower threshold data should rule out one of the two mass ranges for spin-independent couplings (in the worst case, disfavoring one of the masses by still more than 2.6$σ$) and is likely, though not certain, to do the same for spin-dependent couplings. Furthermore, the data may indicate whether the interaction is predominantly spin-independent or spin-dependent in some cases. Our findings illustrate the importance of a low threshold in modulation searches.

astro-ph.CO↗

arXiv2013

Gamma Rays from Bino-like Dark Matter in the MSSM

We consider regions of the parameter space of the Minimal Supersymmetric Standard Model (MSSM) with bino-like neutralino dark matter in which a large fraction of the total dark matter annihilation cross section in the present era arises from annihilation to final states with monoenergetic photons. The region of interest is characterized by light sleptons and heavy squarks. We find that it is possible for the branching fraction to final states with monoenergetic photons to be comparable to that for continuum photons, but in those cases the total cross section will be so small that it is unlikely to be observable. For models where dark matter annihilation may be observable in the present era, the branching fraction to final states with monoenergetic photons is O(1-10%).

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arXiv2013

Closing Supersymmetric Resonance Regions With Direct Detection Experiments

In order for neutralino dark matter to avoid being overproduced in the early universe, these particles must annihilate (or coannihilate) rather efficiently. Neutralinos with sufficiently large couplings to annihilate at such high a rate (such as those resulting from gaugino-higgsino mixing, as in "well-tempered" or "focus point" scenarios), however, have become increasingly disfavored by the null results of XENON100 and other direct detection experiments. One of the few remaining ways that neutralinos could potentially evade such constraints is if they annihilate through a resonance, as can occur if 2$m_{χ^0}$ falls within about $\sim$10% of either $m_{A/H}$, $m_h$, or $m_Z$. If no signal is observed from upcoming direct detection experiments, the degree to which such a resonance must be tuned will increase significantly. In this paper, we quantify the degree to which such a resonance must be tuned in order to evade current and projected constraints from direct detection experiments. Assuming a future rate of progress among direct detection experiments that is similar to that obtained over the past decade, we project that within 7 years the light Higgs and $Z$ pole regions will be entirely closed, while the remaining parameter space near the $A/H$ resonance will require that $2m_{χ^0}$ be matched to the central value (near $m_A$) to within less than 4%. At this rate of progress, it will be a little over a decade before multi-ton direct detection experiments will be able to close the remaining, highly-tuned, regions of the $A/H$ resonance parameter space.

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arXiv2013

Well-Mixed Dark Matter and the Higgs

The breaking of electroweak symmetry through renormalization group flow in models that have MSSM spectra is found to produce "well-mixed" neutralino dark matter with a relic density consistent with the WMAP data and elastic scattering cross section with nuclei consistent with current limits from direct dark matter searches. These models predict a Higgs boson mass in the range (125-126) GeV. Well-mixed neutralino dark matter is predominantly bino-like, but has significant Higgsino and wino content, each with fractions of comparable size. With a ~1 TeV gluino mass and sizable neutralino-nucleon scattering cross sections, natural models will be fully tested by both the LHC and future dark matter direct detection experiments.

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arXiv2012

The Higgs Mass beyond the CMSSM

The apparent discovery of a Higgs boson with mass ~125 GeV has had a significant impact on the constrained minimal supersymmetric extension of the Standard Model in which the scalar masses, gaugino masses and tri-linear A-terms are assumed to be universal at the GUT scale (the CMSSM). Much of the low-mass parameter space in the CMSSM has been excluded by supersymmetric particle searches at the LHC as well as by the Higgs mass measurement and the emergent signal for B_s to mu^+ mu^-. Here, we consider the impact of these recent LHC results on several variants of the CMSSM with a primary focus on obtaining a Higgs mass of ~125 GeV. In particular, we consider the one- and two-parameter extensions of the CMSSM with one or both of the Higgs masses set independently of the common sfermion mass, m_0 (the NUHM1,2). We also consider the one-parameter extension of the CMSSM in which the input universality scale M_in is below the GUT scale (the sub-GUT CMSSM). We find that when M_in < M_GUT large regions of parameter space open up where the relic density of neutralinos can successfully account for dark matter with a Higgs boson mass ~125 GeV. In some of these regions essential roles are played by coannihilation processes that are usually less important in the CMSSM with M_in = M_GUT. Finally, we reconsider mSUGRA models with sub-GUT universality, which have the same number of parameters as the CMSSM. Here too, we find phenomenologically viable regions of parameter space, which are essentially non-existent in GUT-scale mSUGRA models. Interestingly, we find that the preferred range of the A-term straddles that predicted by the simplest Polonyi model.

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arXiv2012

Dark Matter and EWSB Naturalness in Unified SUSY Models

The relationship between the degree of fine-tuning in Electroweak Symmetry Breaking (EWSB) and the discoverability of dark matter in current and next generation direct detection experiments is investigated in the context of two unified Supersymmetry scenarios: the constrained Minimal Supersymmetric Standard Model (CMSSM) and models with non-universal Higgs masses (NUHM). Attention is drawn to the mechanism(s) by which the relic abundance of neutralino dark matter is suppressed to cosmologically viable values. After a summary of Amsel, Freese, and Sandick (2011), results are updated to reflect current constraints, including the discovery of a new particle consistent with a Standard Model-like Higgs boson. We find that a Higgs mass of ~125 GeV excludes the least fine-tuned CMSSM points in our parameter space and that remaining viable models may be difficult to probe with next generation direct dark matter searches. Relatively low fine-tuning and good direct detection prospects are still possible in NUHM scenarios.

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arXiv2012

Gamma-Ray Constraints on the First Stars from Annihilation of Light WIMPs

We calculate the limits on the fraction of viable dark matter minihalos in the early universe to host Population III.1 stars, surviving today as dark matter spikes in our Milky Way halo. Motivated by potential hints of light dark matter from the DAMA and CoGeNT direct dark matter searches, we consider thermal relic WIMP dark matter with masses of 5, 10, and 20 GeV, and annihilation to mu^+ mu^-, tau^+ tau^-, and q bar{q}. From this brief study we conclude that, if dark matter is light, either the typical black hole size is \lesssim 100 M_\odot (i.e. there is no significant Dark Star phase), and/or dark matter annihilates primarily to mu^+ mu^- or other final states that result in low gamma-ray luminosity, and/or that an extremely small fraction of minihalos in the early universe that seem suitable to host the formation of the first stars actually did.

astro-ph.CO↗

arXiv2011

Probing EWSB Naturalness in Unified SUSY Models with Dark Matter

We have studied Electroweak Symmetry Breaking (EWSB) fine-tuning in the context of two unified Supersymmetry scenarios: the Constrained Minimal Supersymmetric Model (CMSSM) and models with Non-Universal Higgs Masses (NUHM), in light of current and upcoming direct detection dark matter experiments. We consider both those models that satisfy a one-sided bound on the relic density of neutralinos, $Ω_χ h^2 < 0.12$, and also the subset that satisfy the two-sided bound in which the relic density is within the 2 sigma best fit of WMAP7 + BAO + H0 data. We find that current direct detection searches for dark matter probe the least fine-tuned regions of parameter-space, or equivalently those of lowest Higgs mass parameter $μ$, and will tend to probe progressively more and more fine-tuned models, though the trend is more pronounced in the CMSSM than in the NUHM. Additionally, we examine several subsets of model points, categorized by common mass hierarchies; $M_{χ_0} \sim M_{χ^\pm}, M_{χ_0} \sim M_{\stau}, M_{χ_0} \sim M_{\stop_1}$, the light and heavy Higgs poles, and any additional models classified as "other"; the relevance of these mass hierarchies is their connection to the preferred neutralino annihilation channel that determines the relic abundance. For each of these subsets of models we investigated the degree of fine-tuning and discoverability in current and next generation direct detection experiments.

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arXiv2011

Detection Prospects for Majorana Fermion WIMPless Dark Matter

We consider both velocity-dependent and velocity-independent contributions to spin-dependent (SD) and spin-independent (SI) nuclear scattering (including one-loop corrections) of WIMPless dark matter, in the case where the dark matter candidate is a Majorana fermion. We find that spin-independent scattering arises only from the mixing of exotic squarks, or from velocity-dependent terms. Nevertheless (and contrary to the case of MSSM neutralino WIMPs), we find a class of models which cannot be detected through SI scattering, but can be detected at IceCube/DeepCore through SD scattering. We study the detection prospects for both SI and SD detection strategies for a large range of Majorana fermion WIMPless model parameters.

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arXiv2011

Black Holes in our Galactic Halo: Compatibility with FGST and PAMELA Data and Constraints on the First Stars

10 to 10^5 solar mass black holes with dark matter spikes that formed in early minihalos and still exist in our Milky Way Galaxy today are examined in light of recent data from the Fermi Gamma-Ray Space Telescope (FGST). The dark matter spikes surrounding black holes in our Galaxy are sites of significant dark matter annihilation. We examine the signatures of annihilations into gamma-rays, electrons and positrons, and neutrinos. We find that some significant fraction of the point sources detected by FGST might be due to dark matter annihilation near black holes in our Galaxy. We obtain limits on the properties of dark matter annihilations in the spikes using the information in the FGST First Source Catalog as well as the diffuse gamma-ray flux measured by FGST. We determine the maximum fraction of high redshift minihalos that could have hosted the formation of the first generation of stars and, subsequently, their black hole remnants. The strength of the limits depends on the choice of annihilation channel and black hole mass; limits are strongest for the heaviest black holes and annhilation to $b \bar{b}$ and $W^+W^-$ final states. The larger black holes considered in this paper may arise as the remnants of Dark Stars after the dark matter fuel is exhausted and thermonuclear burning runs its course; thus FGST observations may be used to constrain the properties of Dark Stars. Additionally, we comment on the excess positron flux found by PAMELA and its possible interpretation in terms of dark matter annihilation around these black hole spikes.

astro-ph.CO↗

arXiv2011

Constraints on a Non-thermal History from Galactic Dark Matter Spikes

In this paper we examine whether indirect detection constraints on dark matter associated with a non-thermal history may be significantly improved when accounting for the presence of galactic substructure in the form of dark matter spikes. We find that significant constraints may be derived from the non-observation of an excess of diffuse gamma-rays and from the properties of bright gamma-ray point sources observed by the Fermi Gamma-Ray Space Telescope, but these constraints depend sensitively on the details of the formation of the first stars and their subsequent black hole remnants. However, we also find that, especially if WIMPs annihilate primarily to quarks or gauge bosons, it is possible to extract meaningful and conservative bounds on the annihilation cross section.

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