arXiv subjects

Christopher Dessert

Publications and source records attributed to Christopher Dessert.

22 records · Page 2Linked to original sources

arXiv2021

The dark matter interpretation of the 3.5-keV line is inconsistent with blank-sky observations

Observations of nearby galaxies and galaxy clusters have reported an unexpected X-ray emission line around 3.5 kilo-electron volts (keV). Proposals to explain this line include decaying dark matter$-$in particular, that the decay of sterile neutrinos with a mass around 7 keV could match the available data. If this interpretation is correct, the 3.5 keV line should also be emitted by dark matter in the halo of the Milky Way. We used more than 30 megaseconds of XMM-Newton (X-ray Multi-Mirror Mission) blank-sky observations to test this hypothesis, finding no evidence of the 3.5-keV line emission from the Milky Way halo. We set an upper limit on the decay rate of dark matter in this mass range, which is inconsistent with the possibility that the 3.5-keV line originates from dark matter decay.

astro-ph.CO↗

arXiv2020

Hard X-ray Excess from the Magnificent Seven Neutron Stars

We report significant hard X-ray excesses in the energy range 2-8 keV for two nearby isolated neutron stars RX J1856.6-3754 and RX J0420.0-5022. These neutron stars have previously been observed in soft X-rays to have nearly thermal spectra at temperatures ~100 eV, which are thought to arise from the warm neutron star surfaces. We find nontrivial hard X-ray spectra well above the thermal surface predictions with archival data from the XMM-Newton and Chandra X-ray telescopes. We analyze possible systematic effects that could generate such spurious signals, such as nearby X-ray point sources and pileup of soft X-rays, but we find that the hard X-ray excesses are robust to these systematics. We also investigate possible sources of hard X-ray emission from the neutron stars and find no satisfactory explanation with known mechanisms, suggesting that a novel source of X-ray emission is at play. We do not find high-significance hard X-ray excesses from the other five Magnificent Seven isolated neutron stars.

astro-ph.HE↗

arXiv2020

Systematics in the XENON1T data: the 15-keV anti-axion

The XENON1T collaboration has found an excess of electron recoil events in their Science Run 1 data below ~7 keV with a spectral shape consistent with that expected from a solar-axion-induced signal. The claimed statistical significance of the solar-axion model over the null hypothesis is 3.5$σ$. In this work we provide evidence for mismodeling in the electron recoil data that may decrease the local significance of the axion model to as low as $p \approx 0.1$. To reach this conclusion, we search for a signal with the spectral template of the solar axion model, but shifted to higher (unphysical) energies above ~7 keV. We find that the distribution of significances found from this side-band analysis does not follow the expected chi-square distribution, which allows us to quantify the extent to which mismodeling may be affecting the interpretation of the data at energies below ~7 keV. For example, we find that there is an even higher-significance fit to the data when the solar axion model is shifted upwards in energy by ~15 keV and allowed to have a negative normalization.

hep-ph↗

arXiv2019

Addressing Astrophysical and Cosmological Problems With Secretly Asymmetric Dark Matter

We present a simple model of dark matter that can address astrophysical and cosmological puzzles across a wide range of scales. The model is an application of the Secretly Asymmetric Dark Matter mechanism, where several flavors of dark matter are fully asymmetric despite an exact dark matter number symmetry $U(1)_χ$. The dark matter relic abundance arises from these asymmetries, generated in the early universe through right-handed neutrino decays. The $U(1)_χ$ is gauged by a massless dark photon, and asymmetries with opposite signs in the different DM flavors result in the formation of bound states. Dark acoustic oscillations in the early universe lead to a suppression in the matter power spectrum for addressing the $σ_8$ problem. The dark photon as a relativistic degree of freedom contributes to $ΔN_{eff}$, easing the tension between the CMB and late-time $H_{0}$ measurements. Finally, scattering between the bound states after structure formation leads to a flattening of the dark matter distribution at the cores of haloes.

hep-ph↗