arXiv subjects

Gabrijela Zaharijas

Publications and source records attributed to Gabrijela Zaharijas.

46 records · Page 3Linked to original sources

arXiv2007

Prospects For Detecting Dark Matter With GLAST In Light Of The WMAP Haze

Observations by the WMAP experiment have identified an excess of microwave emission from the center of the Milky Way. It has previously been shown that this "WMAP Haze" could be synchrotron emission from relativistic electrons and positrons produced in the annihilations of dark matter particles. In particular, the intensity, spectrum and angular distribution of the WMAP Haze is consistent with an electroweak scale dark matter particle (such as a supersymmetric neutralino or Kaluza-Klein dark matter in models with universal extra dimensions) annihilating with a cross section on the order of sigma v~3x10^-26 cm^3/s and distributed with a cusped halo profile. No further exotic astrophysical or annihilation boost factors are required. If dark matter annihilations are in fact responsible for the observed Haze, then other annihilation products will also be produced, including gamma rays. In this article, we study the prospects for the GLAST satellite to detect gamma rays from dark matter annihilations in the Galactic Center region in this scenario. We find that by studying only the inner 0.1 degrees around the Galactic Center, GLAST will be able to detect dark matter annihilating to heavy quarks or gauge bosons over astrophysical backgrounds with 5sigma (3sigma) significance if they are lighter than approximately 320-500 GeV (500-750 GeV). If the angular window is broadened to study the dark matter halo profile's angular extension (while simultaneously reducing the astrophysical backgrounds), WIMPs as heavy as several TeV can be identified by GLAST with high significance. Only if the dark matter particles annihilate mostly to electrons or muons will GLAST be unable to identify the gamma ray spectrum associated with the WMAP Haze.

astro-ph↗

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.

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↗

arXiv2005

Dark Matter and the Baryon Asymmetry

We present a mechanism to generate the baryon asymmetry of the Universe which preserves the net baryon number created in the Big Bang. If dark matter particles carry baryon number $B_X$, and $σ^{\rm annih}_{\bar{X}} < σ^{\rm annih}_{X} $, the $\bar{X}$'s freeze out at a higher temperature and have a larger relic density than $X$'s. If $m_X \lsi 4.5 B_X $GeV and the annihilation cross sections differ by $\mathcal{O}$(10%) or more, this type of scenario naturally explains the observed $Ω_{DM} \approx 5 Ω_b$. Two concrete examples are given, one of which can be excluded on observational grounds.

hep-ph↗

arXiv2005

Alternative Approaches to Dark Matter Puzzle

We study the dark matter problem with particular reference to a candidate particle within the Standard Model: the $H$ dibaryon. We consider as well a scenario which aims to connect the dark matter origin to the Baryon Asymmetry of the Universe, studying the examples of $H$ and of a BSM particle $X$. Strongly attractive color forces in the flavor singlet channel may lead to a tightly bound and compact $H$ dibaryon. We find that the observation of $Λ$ decays from doubly-strange hypernuclei puts a constraint on the $H$ wavefunction which is plausibly satisfied. In this case the $H$ is long-lived as we calculate. We also show that an $H$ or another compact, flavor singlet hadron is unlikely to bind to nuclei, so that experimental bounds on exotic isotopes do not exclude their existence. Remarkably, the $H$ appears to evade other experimental constraints as well, when account is taken of its expected compact spatial wavefunction. We check whether the $H$ is a viable DM candidate by considering DM experiments sensitive to light particles. Taking into account the DM interaction in the crust above underground detectors we find a window in the exclusion limits in the micro-barn, $m\lsi 2.4$ GeV, range which coincides with the range expected for the tightly bound $H$. Finally, we present a scenario in which DM carries (anti-)baryon number and which offers a mechanism to generate the baryon asymmetry observed in the Universe. If $σ^{annih} _{\bar{X}} < σ^{annih}_{X}$, the $\bar{X}$'s freeze out at a higher temperature and have a larger relic density than $X$'s. If $m_X \lsi 4.5 B_X$ GeV and the annihilation cross sections differ by 10% or more, this type of scenario naturally explains the observed $Ω_{DM} \simeq 5 Ω_b$. Two examples are given, the $H$ and an hypothetical BSM candidate $X$.

astro-ph↗

arXiv2005

A Window in the Dark Matter Exclusion Limits

We consider the cross section limits for light dark matter candidates ($m=0.4$ to 10 GeV). We calculate the interaction of dark matter in the crust above underground dark matter detectors and find that in the intermediate cross section range, the energy loss of dark matter is sufficient to fall below the energy threshold of current underground experiments. This implies the existence of a window in the dark matter exclusion limits in the micro-barn range.

astro-ph↗

arXiv2004

Dark Matter and the Baryon Asymmetry of the Universe

We present a mechanism to generate the baryon asymmetry of the Universe which preserves the net baryon number created in the Big Bang. If dark matter particles carry baryon number $B_X$, and $σ^{\rm annih}_{\bar{X}} < σ^{\rm annih}_{X} $, the $\bar{X}$'s freeze out at a higher temperature and have a larger relic density than $X$'s. If $m_X \lsi 4.5 B_X $GeV and the annihilation cross sections differ by $\gsi 10%$, this type of scenario naturally explains the observed $Ω_{DM} \approx 5 Ω_b$.

hep-ph↗

arXiv2003

Nuclear and nucleon transitions of the H di-baryon

We consider 3 types of processes pertinent to the phenomenology of an H di-baryon: conversion of two $Λ$'s in a doubly-strange hypernucleus to an H, decay of the H to two baryons, and -- if the H is light enough -- conversion of two nucleons in a nucleus to an H. We compute the spatial wavefunction overlap using the Isgur-Karl and Bethe-Goldstone wavefunctions, and treat the weak interactions phenomenologically. The observation of $Λ$ decays from doubly-strange hypernuclei puts a constraint on the H wavefunction which is plausibly satisfied. In this case the H is very long-lived as we calculate. An absolutely stable H is not excluded at present. SuperK can provide valuable limits.

hep-ph↗

arXiv2003

Transitions of two baryons to the H dibaryon in nuclei

We calculate the suppression in the rate at which two baryons in a nucleus (viz., nucleons or $Λ$'s) convert to an H dibaryon, using an Isgur-Karl wavefunction for quarks in the baryons and H, and a Bethe-Goldstone wavefunction for the baryons in the nucleus. If $r_H \lsi 1/3~ r_N$, we find $τ_{A_{ΛΛ}\to A'_H}\gsi τ_Λ$ and the observation of $Λ$ decays from double-$Λ$ hypernuclei does not exclude the existence of the H. If $m_H < 2 m_p$, nuclei are unstable but have very long lifetimes. For reasonable values of $r_H$ and the nuclear wavefunction, the lifetime can be long enough to evade anticipated SuperK limits $τ_{A_{NN}\to A'_H}\gsi {\rm few} 10^{29}$ yr, or short enough to be observed. An analysis of SuperK data to look for this possibility should be undertaken.

hep-ph↗

arXiv2003

Non-binding of Flavor-Singlet Hadrons to Nuclei

Strongly attractive color forces in the flavor singlet channel may lead to a stable H dibaryon. Here we show that an H or other compact, flavor singlet hadron is unlikely to bind to nuclei, so that bounds on exotic isotopes do not exclude their stability. Remarkably, a stable H appears to evade other experimental constraints as well, when account is taken of its expected compact spatial wavefunction.

hep-ph↗