arXiv subjects

Arpan Kar

Publications and source records attributed to Arpan Kar.

24 records · Page 2Linked to original sources

arXiv2020

Dark matter annihilation in $ω$ Centauri: Astrophysical implications derived from the MWA radio data

We present an analysis of Murchison Widefield Array radio telescope data from $ω$ Cen, possibly a stripped dwarf spheroidal galaxy core captured by our Galaxy. Recent interpretations of Fermi-LAT $γ$-ray data by Brown {\it et al.} (2019) and Reynoso-Cordova {\it et al.} (2019) suggest that $ω$ Cen may contain significant Dark Matter. We utilise their best-fit Dark Matter annihilation models, and an estimate of the magnetic field strength in $ω$ Cen, to calculate the expected radio synchrotron signal from annihilation, and show that one can usefully rule out significant parts of the magnetic field - diffusion coefficient plane using our current observational limits on the radio emission. Improvement by a factor of 10-100 on these limits could constrain the models even more tightly.

astro-ph.HE↗

arXiv2020

Heavy dark matter particle annihilation in dwarf spheroidal galaxies: radio signals at the SKA telescope

A weakly interacting dark matter candidate is difficult to detect at high-energy colliders like the LHC, if its mass is close to, or higher than a TeV. On the other hand, pair-annihilation of such particles may give rise to $e^+ e^-$ pairs in dwarf spheroidal galaxies (dSph), which in turn can lead to radio synchrotron signals that are detectable at the upcoming Square Kilometre Array (SKA) telescope within a moderate observation time. We investigate the circumstances under which this complementarity between collider and radio signals of dark matter can be useful in probing physics beyond the standard model of elementary particles. Both particle physics issues and the roles of diffusion and electromagnetic energy loss of the $e^\pm$ are taken into account. First, the criteria for detectability of trans-TeV dark matter are analysed independently of the particle physics model(s) involved. We thereafter use some benchmarks based on a popular scenario, namely, the minimal supersymmetric standard model. It is thus shown that the radio flux from a dSph like Draco should be observable in about 100 hours at the SKA, for dark matter masses upto 4-8 TeV. In addition, the regions in the space spanned by astrophysical parameters, for which such signals should be detectable at the SKA, are marked out.

hep-ph↗

arXiv2019

Constraints on dark matter annihilation in dwarf spheroidal galaxies from low frequency radio observations

We present the first observational limits on the predicted synchrotron signals from particle Dark Matter annihilation models in dwarf spheroidal galaxies at radio frequencies below 1 GHz. We use a combination of survey data from the Murchison Widefield Array (MWA) and the Giant Metre-wave Radio Telescope (GMRT) to search for diffuse radio emission from 14 dwarf spheroidal galaxies. For in-situ magnetic fields of 1 $μG$ and any plausible value for the diffusion coefficient, our limits do not constrain any Dark Matter models. However, for stronger magnetic fields our data might provide constraints comparable to existing limits from gamma-ray and cosmic ray observations. Predictions for the sensitivity of the upgraded MWA show that models with Dark Matter particle mass up to $\sim$ 1.6 TeV (1 TeV) may be constrained for magnetic field of 2 $μG$ (1 $μG$). While much deeper limits from the future low frequency Square Kilometre Array (SKA) will challenge the LHC in searches for Dark Matter particles, the MWA provides a valuable first step toward the SKA at low frequencies.

astro-ph.HE↗

arXiv2019

Can SKA--Phase 1 go much beyond the LHC in supersymmetry search?

We study the potential of the Square Kilometre Array in the first phase (SKA1) in detecting dark matter annihilation signals from dwarf spheroidals in the form of diffuse radio synchrotron. Taking the minimal supersymmetric standard model as illustration, we show that it is possible to detect such signals for dark matter masses about an order of magnitude beyond the reach of the Large Hadron Collider, with about 100 hours of observation with the SKA1.

hep-ph↗

arXiv2018

Dark matter, extra-terrestrial gamma-rays and the MSSM: a viability study

We fit the $γ$-ray excess from the galactic centre (GC) in terms of parameters of the minimal supersymmetric standard model (MSSM). Consistency with other $γ$-ray observation, such as those from dwarf spheroidal galaxies, is also ensured, in addition to the constraints from direct dark matter search. Furthermore, we expect the contribution to the relic density from the MSSM dark mater candidate, namely, the lightest neutralino, should not go below the stipulated value; otherwise it will amount to going beyond the MSSM by including some additional dark matter source. After a detailed scan of the parameter space in terms of four representative types of particle spectra, we identify the ones that are best fit to the observed data. However, these two are somewhat unsatisfactory in terms of $χ^2_{min}$ as well as $p$-values. In some case(s), the unacceptability of low-$χ^2_{min}$ regions due to direct search constraint is responsible for this. In others, the observed shape of the $γ$-ray spectrum makes the fits unsatisfactory. The imposed lower limit on relic density, too, has a role to play all along. On the whole, the conclusion is that the MSSM is not a very satisfactory fit for the GC $γ$-ray compounded with other cosmological observations and direct search limits.

hep-ph↗

arXiv2017

Do astrophysical data disfavour the minimal supersymmetric standard model?

If the minimal supersymmetric standard model (MSSM) is the only new physics around the TeV-scale, it has to account for the entire dark matter relic density, or else it will cease to be `minimal'. We use this expectation to obtain the best quantitative explanation of the galactic centre $γ$-ray excess. The $γ$-ray data/flux limits from other astrophysical sources are also taken into account, together with all laboratory constraints. The lower limit on the relic density, together with the latest direct dark matter search constraints and the shape of the galactic centre $γ$-ray spectrum, makes the MSSM fits appear rather poor. A comparison with similar fits of the Higgs boson mass from indirect and direct search results makes one suspicious that the MSSM is not a good explanation of data related to dark matter.

hep-ph↗