arXiv subjects

Louis E. Strigari

Publications and source records attributed to Louis E. Strigari.

At least 91 records · Page 5Linked to original sources

arXiv2017

Sommerfeld-Enhanced $J$-Factors For Dwarf Spheroidal Galaxies

For models in which dark matter annihilation is Sommerfeld-enhanced, the annihilation cross section increases at low relative velocities. Dwarf spheroidal galaxies (dSphs) have low characteristic dark matter particle velocities and are thus ideal candidates to study such models. In this paper we model the dark matter phase space of dSphs as isotropic and spherically-symmetric, and determine the $J$-factors for several of the most important targets for indirect dark matter searches. For Navarro-Frenk-White density profiles, we quantify the scatter in the $J$-factor arising from the astrophysical uncertainty in the dark matter potential. We show that, in Sommerfeld-enhanced models, the ordering of the most promising dSphs may be different relative to the standard case of velocity-independent cross sections. This result can have important implications for derived upper limits on the annihilation cross section, or on possible signals, from dSphs.

astro-ph.CO↗

arXiv2016

Planck Constraint on Relic Primordial Black Holes

We investigate constraints on the abundance of primordial black holes (PBHs) in the mass range 10^{15}-10^{17} g using data from the Cosmic Microwave Background (CMB) and MeV extragalactic gamma-ray background (EGB). Hawking radiation from PBHs with lifetime greater than the age of the universe leaves an imprint on the CMB through modification of the ionization history and the damping of CMB anisotropies. Using a model for redshift dependent energy injection efficiencies, we show that a combination of temperature and polarization data from Planck provides the strongest constraint on the abundance of PBHs for masses \sim 10^{15}-10^{16} g, while the EGB dominates for masses \gtrsim 10^{16} g. Both the CMB and EGB now rule out PBHs as the dominant component of dark matter for masses \sim 10^{16}-10^{17} g. Planned MeV gamma-ray observatories are ideal for further improving constraints on PBHs in this mass range.

astro-ph.CO↗

arXiv2016

Probing light mediators at ultra-low threshold energies with coherent elastic neutrino-nucleus scattering

Light neutral mediators, with mass $\lesssim 1$ GeV, are common features of extensions to the Standard Model (SM). Current astrophysical and terrestrial experiments have constrained the model parameter space, and planned experiments around the world promise continued improvement in sensitivity. In this paper we study the prospects for probing light neutral mediators using terrestrial stopped pion and reactor sources in combination with ultra-low threshold nuclear and electron recoil detectors. We show that the coherent neutrino-nucleus and neutrino-electron scattering channels provide complementary sensitivity to light mediators. With low threshold detectors, we show that most stringent bounds on models arise from the nuclear scattering process, improving upon previous bounds from electron scattering of solar neutrinos by nearly an order of magnitude for mediator masses $\gtrsim 0.1$ GeV.

hep-ph↗

arXiv2016

Dynamical models for the Sculptor dwarf spheroidal in a Lambda CDM universe

The Sculptor dwarf spheroidal galaxy contains two distinct stellar populations: one metal-rich and the other metal-poor. Several authors have argued that in order for these two populations to reside in the same gravitational potential, the dark matter halo must have a core similar to that observed in the stellar count profile. This would rule out the cuspy Navarro-Frenk-White (NFW) density profiles predicted for halos and subhalos by dark matter only simulations of the Lambda Cold Dark Matter (Lambda-CDM) cosmological model. We present a new theoretical framework to analyse stellar count and velocity observations in a self-consistent manner based on separable models, f(E,J)=g(J)h(E), for the distribution function of an equilibrium spherical system. We use this machinery to analyse available photometric and kinematic data for the two stellar populations in Sculptor. We find, contrary to some previous claims, that the data are consistent with populations in equilibrium within an NFW dark matter potential with structural parameters in the range expected in Lambda-CDM. Our solution gives a maximum circular velocity for Sculptor between 20 and 35 km/s. We discuss why some previous authors came to a different conclusion.

astro-ph.GA↗

arXiv2016

Tidal features of classical Milky Way satellites in a $Λ$CDM universe

We use the APOSTLE cosmological hydrodynamic simulations to examine the effects of tidal stripping on cold dark matter (CDM) sub haloes that host three of the most luminous Milky Way (MW) dwarf satellite galaxies: Fornax, Sculptor, and Leo I. We identify simulated satellites that match the observed spatial and kinematic distributions of stars in these galaxies, and track their evolution after infall. We find $\sim$ 30$\%$ of subhaloes hosting satellites with present-day stellar mass $10^6$-$10^8$ $M_{\odot}$ experience $>20\%$ stellar mass loss after infall. Fornax analogues have earlier infall times compared to Sculptor and Leo I analogues. Star formation in Fornax analogues continues for $\sim3$-$6$ Gyr after infall, whereas Sculptor and Leo I analogues stop forming stars $< 2$-$3$ Gyr after infall. Fornax analogues typically show more significant stellar mass loss and exhibit stellar tidal tails, whereas Sculptor and Leo I analogues, which are more deeply embedded in their host DM haloes at infall, do not show substantial mass loss due to tides. When additionally comparing the orbital motion of the host subaloes to the measured proper motion of Fornax we find the matching more difficult; host subhaloes tend to have pericentres smaller than that measured for Fornax itself. From the kinematic and orbital data, we estimate that Fornax has lost $10-20\%$ of its infall stellar mass. Our best estimate for the surface brightness of a stellar tidal stream associated with Fornax is $Σ\sim$ 32.6 mag $ {\rm arcsec^{-2}}$, which may be detectable with deep imaging surveys such as DES and LSST.

astro-ph.GA↗

arXiv2016

Sensitivity to oscillation with a sterile fourth generation neutrino from ultra-low threshold neutrino-nucleus coherent scattering

We discuss prospects for probing short-range sterile neutrino oscillation using neutrino-nucleus coherent scattering with ultra-low energy ($\sim 10$ eV - 100 eV) recoil threshold cryogenic Ge detectors. The analysis is performed in the context of a specific and contemporary reactor-based experimental proposal, developed in cooperation with the Nuclear Science Center at Texas A\&M University, and references developing technology based upon economical and scalable detector arrays. The baseline of the experiment is substantially shorter than existing measurements, as near as about 2 meters from the reactor core, and is moreover variable, extending continuously up to a range of about 10 meters. This proximity and variety combine to provide extraordinary sensitivity to a wide spectrum of oscillation scales, while facilitating the tidy cancellation of leading systematic uncertainties in the reactor source and environment. With 100~eV sensitivity, for exposures on the order of 200 kg$\cdot$y, we project an estimated sensitivity to first/fourth neutrino oscillation with a mass gap $Δm^2 \sim 1 \, {\rm eV}^2$ at an amplitude $\sin^2 2θ\sim 10^{-1}$, or $Δm^2 \sim 0.2 \, {\rm eV}^2$ at unit amplitude. Larger exposures, around 5,000 kg$\cdot$y, together with 10 eV sensitivity are capable of probing more than an additional order of magnitude in amplitude.

hep-ph↗

arXiv2016

Dark matter, light mediators, and the neutrino floor

We analyze future direct data matter detection experiments using Effective Field Theory (EFT) operators with light, $\lesssim 100$ MeV mass mediators. We compare the nuclear recoil energy spectra from these operators to the predicted high energy solar neutrino spectrum. A set of operators that generate spectra similar to the neutrino background is identified, however this set is distinct from those that mimic the neutrino background for heavy, $\gtrsim 100$ MeV mass mediators. We outline a general classification scheme based on momentum dependence of the dark matter-nucleus interaction to determine how strong the discovery limit for a given operator saturates in the presence of the neutrino background. Our results highlight the benefit of considering a general theoretical framework regarding dark matter, and motivate continued experimental progress towards lower nuclear recoil energy thresholds.

hep-ph↗

arXiv2016

The neutrino floor at ultra-low threshold

By lowering their energy threshold direct dark matter searches can reach the neutrino floor with experimental technology now in development. The 7Be flux can be detected with $\sim 10$ eV nuclear recoil energy threshold and 50 kg-yr exposure. The pep flux can be detected with $\sim 3$ ton-yr exposure, and the first detection of the CNO flux is possible with similar exposure. The pp flux can be detected with threshold of $\sim$ eV and only $\sim$ kg-yr exposure. These can be the first pure neutral current measurements of the low-energy solar neutrino flux. Measuring this flux is important for low mass dark matter searches and for understanding the solar interior.

astro-ph.CO↗

arXiv2016

Sensitivity to Z-prime and non-standard neutrino interactions from ultra-low threshold neutrino-nucleus coherent scattering

We discuss prospects for probing Z-prime and non-standard neutrino interactions using neutrino-nucleus coherent scattering with ultra-low energy (~ 10 eV) threshold Si and Ge detectors. The analysis is performed in the context of a specific and contemporary reactor-based experimental proposal, developed in cooperation with the Nuclear Science Center at Texas A&M University, and referencing available technology based upon economical and scalable detector arrays. For expected exposures, we show that sensitivity to the Z-prime mass is on the order of several TeV, and is complementary to the LHC search with low mass detectors in the near term. This technology is also shown to provide sensitivity to the neutrino magnetic moment, at a level that surpasses terrestrial limits, and is competitive with more stringent astrophysical bounds. We demonstrate the benefits of combining silicon and germanium detectors for distinguishing between classes of models of new physics, and for suppressing correlated systematic uncertainties.

hep-ph↗

arXiv2016

No $ν$ floors: Effective field theory treatment of the neutrino background in direct dark matter detection experiments

Distinguishing a dark matter interaction from an astrophysical neutrino-induced interaction will be major challenge for future direct dark matter searches. In this paper, we consider this issue within non-relativistic Effective Field Theory (EFT), which provides a well-motivated theoretical framework for determining nuclear responses to dark matter scattering events. We analyze the nuclear energy recoil spectra from the different dark matter-nucleon EFT operators, and compare to the nuclear recoil energy spectra that is predicted to be induced by astrophysical neutrino sources. We determine that for 11 of the 14 possible operators, the dark matter-induced recoil spectra can be cleanly distinguished from the corresponding neutrino-induced recoil spectra with moderate size detector technologies that are now being pursued, e.g., these operators would require 0.5 tonne years to be distinguished from the neutrino background for low mass dark matter. Our results imply that in most models detectors with good energy resolution will be able to distinguish a dark matter signal from a neutrino signal, without the need for much larger detectors that must rely on additional information from timing or direction.

hep-ph↗

arXiv2015

WIMP searches with gamma rays in the Fermi era: challenges, methods and results

The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.

astro-ph.CO↗

arXiv2015

Mass assembly history and infall time of the Fornax dwarf spheroidal galaxy

We use cosmological simulations to identify dark matter subhalo host candidates of the Fornax dwarf spheroidal galaxy using the stellar kinematic properties of Fornax. We consider cold dark matter (CDM), warm dark matter (WDM), and decaying dark matter (DDM) simulations for our models of structure formation. The subhalo candidates in CDM typically have smaller mass and higher concentrations at z = 0 than the corresponding candidates in WDM and DDM. We examine the formation histories of the ~ 100 Fornax candidate subhalos identified in CDM simulations and, using approximate luminosity-mass relationships for subhalos, we find two of these subhalos that are consistent with both the Fornax luminosity and kinematics. These two subhalos have a peak mass over ten times larger than their z = 0 mass. We suggest that in CDM the dark matter halo hosting Fornax must have been severely stripped of mass and that it had an infall time into the Milky Way of ~ 9 Gyr ago. In WDM, we find that candidate subhalos consistent with the properties of Fornax have a similar infall time and a similar degree of mass loss, while in DDM we find a later infall time of ~ 3 - 4 Gyr ago and significantly less mass loss. We discuss these results in the context of the Fornax star formation history, and show that these predicted subhalo infall times can be linked to different star formation quenching mechanisms. This emphasizes the links between the properties of the dark matter and the mechanisms that drive galaxy evolution.

astro-ph.GA↗

arXiv2015

Readout strategies for directional dark matter detection beyond the neutrino background

The search for weakly interacting massive particles (WIMPs) by direct detection faces an encroaching background due to coherent neutrino-nucleus scattering. As the sensitivity of these experiments improves, the question of how to best distinguish a dark matter signal from neutrinos will become increasingly important. A proposed method of overcoming this so-called 'neutrino floor' is to utilize the directional signature that both neutrino and dark matter induced recoils possess. We show that directional experiments can indeed probe WIMP-nucleon cross-sections below the neutrino floor with little loss in sensitivity due to the neutrino background. In particular we find at low WIMP masses (around 6 GeV) the discovery limits for directional detectors penetrate below the non-directional limit by several orders of magnitude. For high WIMP masses (around 100 GeV), the non-directional limit is overcome by a factor of a few. Furthermore we show that even for directional detectors which can only measure 1- or 2-dimensional projections of the 3-dimensional recoil track, the discovery potential is only reduced by a factor of 3 at most. We also demonstrate that while the experimental limitations of directional detectors, such as sense recognition and finite angular resolution, have a detrimental effect on the discovery limits, it is still possible to overcome the ultimate neutrino background faced by non-directional detectors.

astro-ph.CO↗

arXiv2015

Confronting Galactic center and dwarf spheroidal gamma-ray observations with cascade annihilation models

Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation models, we study the compatibility of the dark matter interpretation of the Fermi- LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies. For canonical values of the Milky Way density profile and the local dark matter density, we find that the dark matter interpretation to the Galactic center emission is strongly constrained. However, uncertainties in the dark matter distribution weaken the constraints and leave open dark matter interpretations over a wide range of mass scales.

hep-ph↗

arXiv2015

The Leptoquark Implication from the CMS and IceCube Experiments

The recent excess in the CMS measurements of $eejj$ and $eνjj$ channels and the emergence of PeV comsic neutrino events at the IceCube experiment share an intriguing implication for a leptoquark with a 600-650 GeV mass. We investigate the CMS constraints on the flavor structure of a scenario with the minimal leptoquark Yukawa couplings and correlate such a scenario to the resonant enhancement in the very high energy shower event rates at the IceCube. We find for a single leptoquark, the CMS signals require large couplings to the third generation leptons. This leads to an enhancement in the $ν_τ$-nucleon scattering cross-section and subsequently more $ν_τ$ events at PeV energies. However, a visible enhancement above the Standard Model scattering would require a leptoquark Yukawa coupling larger than one that can be easily tested at the upcoming LHC runs.

hep-ph↗

arXiv2014

Dark Matter from Late Invisible Decays to/of Gravitinos

In this work, we sift a simple supersymmetric framework of late invisible decays to/of the gravitino. We investigate two cases where the gravitino is the lightest supersymmetric particle or the next-to-lightest supersymmetric particle. The next-to-lightest supersymmetric particle decays into two dark matter candidates and has a long lifetime due to gravitationally suppressed interactions. However, because of the absence of any hadronic or electromagnetic products, it satisfies the tight bounds set by big bang nucleosynthesis and cosmic microwaved background. One or both of the dark matter candidates produced in invisible decays can contribute to the amount of dark radiation and suppress perturbations at scales that are being probed by the galaxy power spectrum and the Lyman-alpha forest data. We show that these constraints are satisfied in large regions of the parameter space and, as a result, the late invisible decays to/of the gravitino can be responsible for the entire dark matter relic abundance.

hep-ph↗

arXiv2014

Cosmological Simulations of Decaying Dark Matter: Implications for Small-scale Structure of Dark Matter Halos

We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable non-interacting dark matter particle, with decay lifetime comparable to the Hubble time. We study the effects of the kinematic recoil velocity received by the stable dark matter on the structures of dark matter halos ranging from galaxy-cluster to Milky Way mass scales. For Milky Way-mass halos, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. In general, halos with circular velocities comparable to the magnitude of kick velocity are most strongly affected by decays. We show that decaying dark matter models with lifetimes comparable to Hubble time and recoil speeds about 20-40 km/s can significantly reduce both the abundance of Galactic subhalos and the internal densities of the subhalos. We also compare subhalo circular velocity profiles with observational constraints on the Milky Way dwarf satellite galaxies. Interestingly, we find that decaying dark matter models that do not violate current astrophysical constraints, can significantly mitigate both the well-documented "missing satellites problem" and the more recent "too big to fail problem" associated with the abundances and densities of Local Group dwarf satellite galaxies. A relatively unique feature of late decaying dark matter models is that they predict significant evolution of halos as a function of time. This is an important consideration because at high redshifts, prior to decays, decaying models exhibit the same sequence of structure formation as cold dark matter. We conclude that models of decaying dark matter make predictions that are relevant for the interpretation of observations of small galaxies in the Local Group and can be tested or constrained by the kinematics of Local Group dwarf galaxies as well as by forthcoming large-scale surveys.

astro-ph.CO↗

arXiv2014

Connecting Direct Dark Matter Detection Experiments to Cosmologically Motivated Halo Models

Several direct detection experiments, including recently CDMS-II, have reported signals consistent with 5 to 10 GeV dark matter (DM) that appear to be in tension with null results from XENON and LUX experiments; these indicate a careful review of the theoretical basis, including the galactic DM velocity distribution function (VDF). We establish a VDF parameter space from DM-only cosmological simulations and illustrate that seemingly contradictory experimental results can be made consistent within this parameter space. Future experimental limits should be reported after they are marginalized over a range of VDF parameters.

astro-ph.CO↗