arXiv subjects

Dan Hooper

Publications and source records attributed to Dan Hooper.

At least 235 records · Page 13Linked to original sources

arXiv2007

MeV Dark Matter and Small Scale Structure

WIMPs with electroweak scale masses (neutralinos, etc.) remain in kinetic equilibrium with other particle species until temperatures approximately in the range of 10 MeV to 1 GeV, leading to the formation of dark matter substructure with masses as small as $10^{-4} M_{\odot}$ to $10^{-12} M_{\odot}$. However, if dark matter consists of particles with MeV scale masses, as motivated by the observation of 511 keV emission from the Galactic Bulge, such particles are naturally expected to remain in kinetic equilibrium with the cosmic neutrino background until considerably later times. This would lead to a strong suppression of small scale structure with masses below about $10^7 M_{\odot}$ to $10^4 M_{\odot}$. This cutoff scale has important implications for present and future searches for faint Local Group satellite galaxies and for the missing satellites problem.

astro-ph↗

arXiv2007

Detecting MeV Gauge Bosons With High-Energy Neutrino Telescopes

If annihilating MeV-scale dark matter particles are responsible for the observed 511 keV emission from the Galactic bulge, then new light gauge bosons which mediate the dark matter annihilations may have other observable consequences. In particular, if such a gauge boson exists and has even very small couplings to Standard Model neutrinos, cosmic neutrinos with ~TeV energies will scatter with the cosmic neutrino background through resonant exchange, resulting in a distinctive spectral absorption line in the high-energy neutrino spectrum. Such a feature could potentially be detected by future high-energy neutrino telescopes.

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arXiv2006

Distinguishing Supersymmetry From Universal Extra Dimensions or Little Higgs Models With Dark Matter Experiments

There are compelling reasons to think that new physics will appear at or below the TeV-scale. It is not known what form this new physics will take, however. Although The Large Hadron collider is very likely to discover new particles associated with the TeV-scale, it may be difficult for it to determine the nature of those particles, whether superpartners, Kaluza-Klein modes or other states. In this article, we consider how direct and indirect dark matter detection experiments may provide information complementary to hadron colliders, which can be used to discriminate between supersymmetry, models with universal extra dimensions, and Little Higgs theories. We find that, in many scenarios, dark matter experiments can be effectively used to distinguish between these possibilities.

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arXiv2006

The Interplay Between Collider Searches For Supersymmetric Higgs Bosons and Direct Dark Matter Experiments

In this article, we explore the interplay between searches for supersymmetric particles and Higgs bosons at hadron colliders (the Tevatron and the LHC) and direct dark matter searches (such as CDMS, ZEPLIN, XENON, EDELWEISS, CRESST, WARP and others). We focus on collider searches for heavy MSSM Higgs bosons ($A$, $H$, $H^{\pm}$) and how the prospects for these searches are impacted by direct dark matter limits and vice versa. We find that the prospects of these two experimental programs are highly interrelated. A positive detection of $A$, $H$ or $H^{\pm}$ at the Tevatron would dramatically enhance the prospects for a near future direct discovery of neutralino dark matter. Similarly, a positive direct detection of neutralino dark matter would enhance the prospects of discovering heavy MSSM Higgs bosons at the Tevatron or the LHC. Combining the information obtained from both types of experimental searches will enable us to learn more about the nature of supersymmetry.

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arXiv2006

The intergalactic propagation of ultra-high energy cosmic ray nuclei

We investigate the propagation of ultra-high energy cosmic ray nuclei (A = 1-56) from cosmologically distant sources through the cosmic radiation backgrounds. Various models for the injected composition and spectrum and of the cosmic infra-red background are studied using updated photo-disintegration cross-sections. The observational data on the spectrum and the composition of ultra-high energy cosmic rays are jointly consistent with a model where all of the injected primary cosmic rays are iron nuclei (or a mixture of heavy and light nuclei).

astro-ph↗

arXiv2006

Tidal Destruction of The First Dark Microhalos

We point out that the usual self-similarity in cold dark matter models is broken by encounters with individual normal galactic stars on sub-pc scale. Tidal heating and stripping must have redefined the density and velocity structures of the population of the Earth-mass dark matter halos, which are likely to have been the first bound structures to form in the Universe. The disruption rate depends strongly on {\it galaxy types} and the orbital distribution of the microhalos; in the Milky Way, stochastic radial orbits are destroyed first by stars in the triaxial bulge, microhalos on non-planar retrograde orbits with large pericenters and/or apocenters survive the longest. The final microhalo distribution in the {\it solar neighborhood} is better described as a superposition of filamentry microstreams rather than as a set of discrete spherical clumps in an otherwise homogeneous medium. We discuss its important consequences to our detections of microhalos by direct recoil signal and indirect annihilation signal.

astro-ph↗

arXiv2006

Implications of Direct Dark Matter Constraints for Minimal Supersymmetric Standard Model Higgs Boson Searches at the Tevatron

Searches for the Minimal Supersymmetric Standard Model (MSSM) Higgs bosons are among the most promising channels for exploring new physics at the Tevatron. In particular, interesting regions of large $\tan β$ and small $m_A$ are probed by searches for heavy neutral Higgs bosons, A and H, when they decay to $τ^+ τ^-$ and $b\bar{b}$. At the same time, direct searches for dark matter, such as CDMS, attempt to observe neutralino dark matter particles scattering elastically off nuclei. This can occur through t-channel Higgs exchange, which has a large cross section in the case of large $\tan β$ and small $m_A$. As a result, there is a natural interplay between the heavy, neutral Higgs searches at the Tevatron and the region of parameter space explored by CDMS. We show that if the lightest neutralino makes up the dark matter of our universe, current limits from CDMS strongly constrain the prospects of heavy, neutral MSSM Higgs discovery at the Tevatron (at 3 sigma with 4 fb^-1 per experiment) unless $|μ| \gsim$ 400 GeV. The limits of CDMS projected for 2007 will increase this constraint to $|μ| \gsim$ 800 GeV. On the other hand, if CDMS does observe neutralino dark matter in the near future, it will make the discovery of heavy, neutral MSSM Higgs bosons far more likely at the Tevatron.

hep-ph↗

arXiv2006

Probing low-x QCD with cosmic neutrinos at the Pierre Auger Observatory

The sources of the observed ultra-high energy cosmic rays must also generate ultra-high energy neutrinos. Deep inelastic scattering of these neutrinos with nucleons on Earth probe center-of-mass energies $\sqrt{s} \sim 100$ TeV, well beyond those attainable at terrestrial colliders. By comparing the rates for two classes of observable events, any departure from the benchmark (unscreened perturbative QCD) neutrino-nucleon cross-section can be constrained. Using the projected sensitivity of the Pierre Auger Observatory to quasi-horizontal showers and Earth-skimming tau neutrinos, we show that a `Super-Auger' detector can thus provide an unique probe of strong interaction dynamics.

hep-ph↗

arXiv2006

Determining Supersymmetric Parameters With Dark Matter Experiments

In this article, we explore the ability of direct and indirect dark matter experiments to not only detect neutralino dark matter, but to constrain and measure the parameters of supersymmetry. In particular, we explore the relationship between the phenomenological quantities relevant to dark matter experiments, such as the neutralino annihilation and elastic scattering cross sections, and the underlying characteristics of the supersymmetric model, such as the values of mu (and the composition of the lightest neutralino), m_A and tan beta. We explore a broad range of supersymmetric models and then focus on a smaller set of benchmark models. We find that by combining astrophysical observations with collider measurements, mu can often be constrained far more tightly than it can be from LHC data alone. In models in the A-funnel region of parameter space, we find that dark matter experiments can potentially determine m_A to roughly +/-100 GeV, even when heavy neutral MSSM Higgs bosons (A, H_1) cannot be observed at the LHC. The information provided by astrophysical experiments is often highly complementary to the information most easily ascertained at colliders.

hep-ph↗

arXiv2006

AMANDA Observations Constrain the Ultra-High Energy Neutrino Flux

A number of experimental techniques are currently being deployed in an effort to make the first detection of ultra-high energy cosmic neutrinos. To accomplish this goal, techniques using radio and acoustic detectors are being developed, which are optimally designed for studying neutrinos with energies in the PeV-EeV range and above. Data from the AMANDA experiment, in contrast, has been used to place limits on the cosmic neutrino flux at less extreme energies (up to ~10 PeV). In this letter, we show that by adopting a different analysis strategy, optimized for much higher energy neutrinos, the same AMANDA data can be used to place a limit competitive with radio techniques at EeV energies. We also discuss the sensitivity of the IceCube experiment, in various stages of deployment, to ultra-high energy neutrinos.

astro-ph↗

arXiv2006

Probing Supersymmetric Parameters With Astrophysical Observations

A wide range of techniques have been developed to search for particle dark matter, including direct detection, indirect detection, and collider searches. The prospects for the detection of neutralino dark matter is quite promising for each of these three very different methods. Looking ahead to a time in which these techniques have successfully detected neutralino dark matter, we explore the ability of these observations to determine the parameters of supersymmetry. In particular, we focus on the ability of direct and indirect detection techniques to measure the parameters $μ$ and $m_A$. We find that $μ$ can be much more tightly constrained if astrophysical measurements are considered than by LHC data alone. In supersymmetric models within the $A$-funnel region of parameter space, we find that astrophysical measurements can determine $m_A$ to roughly $\pm100$ GeV precision.

hep-ph↗

arXiv2006

Challenges in Detecting Gamma-Rays From Dark Matter Annihilations in the Galactic Center

Atmospheric Cerenkov Telescopes, including HESS and MAGIC, have detected a spectrum of gamma-rays from the galactic center region which extends from $\sim$200 GeV or lower, to at least $\sim$10 TeV. Although the source of this radiation is not yet known, the spectrum appears to behave as a simple power-law, which is not the expectation for gamma-rays generated through the annihilation of dark matter particles. If instead we conclude that the source of these gamma-rays is astrophysical in origin, this spectrum will constitute a background for future dark matter searches using gamma-rays from this region. In this paper we study how this background will affect the prospects for experiments such as GLAST to detect dark matter in the galactic center. We find that only a narrow range of dark matter annihilation rates are potentially observable by GLAST given this newly discovered background and considering current constraints from EGRET and HESS. We also find that a detection of line emission, while not completely ruled out, is only possible for a very narrow range of dark matter models and halo profiles.

astro-ph↗

arXiv2006

Pierre Auger Data, Photons, and Top-Down Cosmic Ray Models

We consider the ultra-high energy cosmic ray (UHECR) spectrum as measured by the Pierre Auger Observatory. Top-down models for the origin of UHECRs predict an increasing photon component at energies above about $10^{19.7}$eV. Here we present a simple prescription to compare the Auger data with a prediction assuming a pure proton component or a prediction assuming a changing primary component appropriate for a top-down model. We find that the UHECR spectrum predicted in top-down models is a good fit to the Auger data. Eventually, Auger will measure a composition-independent spectrum and will be capable of either confirming or excluding the quantity of photons predicted in top-down models.

astro-ph↗

arXiv2006

Constraints on Light Dark Matter From Core-Collapse Supernovae

We show that light ($\simeq$ 1 -- 30 MeV) dark matter particles can play a significant role in core-collapse supernovae, if they have relatively large annihilation and scattering cross sections, as compared to neutrinos. We find that if such particles are lighter than $\simeq$ 10 MeV and reproduce the observed dark matter relic density, supernovae would cool on a much longer time scale and would emit neutrinos with significantly smaller energies than in the standard scenario, in disagreement with observations. This constraint may be avoided, however, in certain situations for which the neutrino--dark matter scattering cross sections remain comparatively small.

hep-ph↗

arXiv2006

Dark Matter and Gamma-Rays From Draco: MAGIC, GLAST and CACTUS

The dwarf spheroidal galaxy Draco has long been considered likely to be one of the brightest point sources of gamma-rays generated through dark matter annihilations. Recent studies of this object have found that it remains largely intact from tidal striping, and may be more massive than previously thought. In this article, we revisit Draco as a source of dark matter annihilation radiation, with these new observational constraints in mind. We discuss the prospects for the experiments MAGIC and GLAST to detect dark matter in Draco, as well as constraints from the observations of EGRET. We also discuss the possibility that the CACTUS experiment has already detected gamma-rays from Draco. We find that it is difficult to generate the flux reported by CACTUS without resorting to non-thermally produced WIMPs and/or a density spike in Draco's dark matter distribution due to the presence of an intermediate mass black hole. We also find that for most annihilation modes, a positive detection of Draco by CACTUS would be inconsistent with the lack of events seen by EGRET.

hep-ph↗

arXiv2005

Light Neutralino Dark Matter in the NMSSM

Neutralino dark matter is generally assumed to be relatively heavy, with a mass near the electroweak scale. This does not necessarily need to be the case, however. In the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and other supersymmetric models with an extended Higgs sector, a very light CP-odd Higgs boson can naturally arise making it possible for a very light neutralino to annihilate efficiently enough to avoid being overproduced in the early Universe. In this article, we explore the characteristics of a supersymmetric model needed to include a very light neutralino, 100 MeV $< \mcnone <$ 20 GeV, using the NMSSM as a prototype. We discuss the most important constraints from Upsilon decays, $b \to s γ$, $B_s \to μ^+ μ^-$ and the magnetic moment of the muon, and find that a light bino or singlino neutralino is allowed, and can be generated with the appropriate relic density. It has previously been shown that the positive detection of dark matter claimed by the DAMA collaboration can be reconciled with other direct dark matter experiments such as CDMS II if the dark matter particle is rather light, between about 6 and 9 GeV. A singlino or bino-like neutralino could easily fall within this range of masses within the NMSSM. Additionally, models with sub-GeV neutralinos may be capable of generating the 511 keV gamma-ray emission observed from the galactic bulge by the INTEGRAL/SPI experiment. We also point out measurements which can be performed immediately at CLEO, BaBar and Belle using existing data to discover or significantly constrain this scenario.

hep-ph↗

arXiv2005

What Can Gamma Ray Bursts Teach Us About Dark Energy?

It has been suggested that Gamma Ray Bursts (GRB) may enable the expansion rate of our Universe to be measured out to very high redshifts ($z \gsim 5$) just as type Ia supernovae have done at $z \sim$1--1.5. We explore this possibility here, and find that GRB have the potential to detect dark energy at high statistical significance, but they are unlikely to be competitive with future supernovae missions, such as SNAP, in measuring the properties of the dark energy. The exception to this conclusion is if there is appreciable dark energy at early times, in which case the information from GRB's will provide an excellent complement to the $z\sim 1$ information from supernovae.

astro-ph↗

arXiv2005

Improved Bounds on Universal Extra Dimensions and Consequences for LKP Dark Matter

We study constraints on models with a flat "Universal'' Extra Dimension in which all Standard Model fields propagate in the bulk. A significantly improved constraint on the compactification scale is obtained from the extended set of electroweak precision observables accurately measured at LEP1 and LEP2. We find a lower bound of M_c = R^{-1} > 700 (800) GeV at the 99% (95%) confidence level. We also discuss the implications of this constraint on the prospects for the direct and indirect detection of Kaluza-Klein dark matter in this model.

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