arXiv subjects

Anirban Biswas

Publications and source records attributed to Anirban Biswas.

42 records · Page 3Linked to original sources

arXiv2016

Explaining Low Energy $γ$-ray Excess from the Galactic Centre using a Two Component Dark Matter Model

Over the past few years, there has been a hint of the $γ$-ray excess observed by the Fermi-LAT satellite borne telescope from the regions surrounding the Galactic Centre at an energy range $\sim 1$-$3$ GeV. The nature of this excess $γ$-ray spectrum is found to be consistent with the $γ$-ray emission expected from dark matter annihilation at the Galactic Centre while disfavouring other known astrophysical sources as the possible origin of this phenomena. It is also reported that the spectrum and morphology of this excess $γ$-rays can well be explained by the dark matter particles having mass in the range $30\sim 40$ GeV annihilating significantly into ${\rm b} \bar{\rm b}$ final state with an annihilation cross section $σ{\rm v}\sim (1.4$ - $2.0)\times 10^{-26}$ cm$^3/$s at the Galactic Centre. In this work, we propose a two component dark matter model where two different types of dark matter particles namely a complex scalar and a Dirac fermion are considered. The stability of both the dark sector particles are maintained by virtue of an additional local U$(1)_{\rm X}$ gauge symmetry. We find that our proposed scenario can provide a viable explanation for this anomalous excess $γ$-rays besides satisfying all the existing relevant theoretical as well as experimental and observational bounds from LHC, PLANCK and LUX collaborations. The allowed range of "effective annihilation cross section" of lighter dark matter particle for the ${\rm b} \bar{\rm b}$ annihilation channel thus obtained, is finally compared with the limits reported by the Fermi-LAT and DES collaborations using data from various dwarf spheroidal galaxies.

hep-ph↗

arXiv2016

Dwarf Galaxy $γ$-excess and 3.55 keV X-ray Line In A Nonthermal Dark Matter Model

Recent data from Reticulum II (RetII) require the energy range of the FermiLAT $γ$-excess to be $\sim$ $2-10$ GeV. We adjust our unified nonthermal Dark Matter (DM) model to accommodate this. We have two extra scalars beyond the Standard Model to also explain 3.55 keV X-ray line. Now the mass of the heavier of them has to be increased to lie around 250 GeV, while that of the lighter one remains at 7.1 keV. This requires a new seed mechanism for the $γ$-excess and new Boltzmann equations for the generation of the DM relic density. All concerned data for RetII and the X-ray line can now be fitted well and consistency with other indirect limits attained.

hep-ph↗

arXiv2015

Nonthermal Two Component Dark Matter Model for Fermi-LAT $γ$-ray excess and 3.55 keV X-ray Line

A two component model of nonthermal dark matter is formulated to simultaneously explain the Fermi-LAT results indicating a $γ$-ray excess observed from our Galactic Centre in the 1-3 GeV energy range and the detection of an X-ray line at 3.55 keV from extragalactic sources. Two additional Standard Model singlet scalar fields $S_2$ and $S_3$ are introduced. These fields couple among themselves and with the Standard Model Higgs doublet $H$. The interaction terms among the scalar fields, namely $H$, $S_2$ and $S_3$, are constrained by the application of a discrete $\mathbb{Z}_2\times \mathbb{Z}^\prime_2$ symmetry which breaks softly to a remnant $\mathbb{Z}^{\prime \prime}_2$ symmetry. This residual discrete symmetry is then spontaneously broken through an MeV order vacuum expectation value $u$ of the singlet scalar field $S_3$. The resultant physical scalar spectrum has the Standard Model like Higgs as $χ_{{}_{{}_1}}$ with $M_{χ_{{}_{{}_1}}}\sim 125$ GeV, a moderately heavy scalar $χ_{{}_{{}_2}}$ with $50 \,\,{\rm GeV} \leq M_{χ_{{}_{{}_2}}}\leq 80\,\,{\rm GeV}$ and a light $χ_{{}_{{}_3}}$ with $M_{χ_{{}_{{}_3}}} \sim 7$ keV. There is only tiny mixing between $χ_{{}_{{}_1}}$ and $χ_{{}_{{}_2}}$ as well as between $χ_{{}_{{}_1}}$ and $χ_{{}_{{}_3}}$. The lack of importance of domain wall formation in the present scenario from the spontaneous breaking of the discrete symmetry ${\mathbb{Z}_2^{\prime\prime}}$, provided $u\leq 10$ MeV, is pointed out. We find that our proposed two component dark matter model is able to explain successfully both the above mentioned phenomena $-$ the Fermi-LAT observed $γ$-ray excess (from the $χ_{{}_{{}_2}} \rightarrow {\rm b} \bar{\rm b}$ decay mode) and the observation of the X-ray line (from the decay channel $χ_{{}_{{}_3}}\rightarrowγγ$) by the XMM-Newton observatory.

hep-ph↗

arXiv2013

Two Component Dark Matter : A Possible Explanation of 130 GeV γ-Ray Line from the Galactic Centre

Recently there has been a hint of a gamma-ray line at 130 GeV originated from the galactic centre after the analysis of the Fermi-LAT satellite data. Being monochromatic in nature, it rules out the possibility of having its astrophysical origin and there has been a speculation that this line could be originated from dark matter annihilation. In this work, we propose a two component dark matter scenario where an extension of the Standard model by an inert Higgs doublet and a gauge singlet scalar concocted with $\rm {Z_2 \times Z^{\prime}_2}$ symmetry, is considered. We find that our scenario can not only explain the 130 GeV gamma-ray line through dark matter annihilation but also produce the correct dark matter relic density. We have used the Standard Model Higgs mass around 125 GeV as intimated by the LHC data..

hep-ph↗

arXiv2013

The Real Gauge Singlet Scalar Extension of Standard Model: A Possible Candidate of Cold Dark Matter

We consider a simplest extension of Standard Model in which a real SM gauge singlet scalar with an additional discrete symmetry $Z_2$ is introduced to SM. This additional scalar can be a viable candidate of cold dark matter since the stability of $S$ is achieved by the application of $Z_2$ symmetry on $S$. Considering $S$ as a possible candidate of cold dark matter we have solved Boltzmann's equation to find the freeze out temperature and relic density of $S$ for Higgs mass 120 GeV in the scalar mass range 5 GeV to 1 TeV. As $HHSS$ coupling $δ_2$ appearing in Lagrangian depends upon the value of scalar mass $m_S$ and Higgs mass $m_h$, we have constrained the $m_S - δ_2$ parameter space by using the WMAP limit on the relic density of dark matter in the universe and the results of recent ongoing dark matter direct search experiments namely CDMS-II, CoGeNT, DAMA, EDELWEISS-II, XENON-10, XENON-100. From such analysis we find two distinct mass regions (a lower and higher mass domain) for such a dark matter candidate that satisfy both the WMAP limit and the experimental results considered here. We have estimated the possible differential direct detection rates and annual variation of total detection rates for this scalar dark matter candidate $S$ for two detector materials namely Ge, Xe. Finally we have calculated the $γ-$ray flux from the galactic centre due to annihilation of two 130 GeV scalar dark matter into two monoenergetic $γ-$rays.

hep-ph↗

arXiv2001

Turbulent Compressibilty of Protogalactic Gas

The star formation rate in galaxies should be related to the fraction of gas that can attain densities large enough for gravitational collapse. In galaxies with a turbulent interstellar medium, this fraction is controlled by the effective barotropic index $gamma = dlog P/dlog (rho)$ which measures the turbulent compressibility. When the cooling timescale is smaller than the dynamical timescale, gamma can be evaluated from the derivatives of cooling and heating functions, using the condition of thermal equilibrium. We present calculations of gamma for protogalaxies in which the metal abundance is so small that H_2 and HD cooling dominates. For a heating rate independent of temperature and proportional to the first power of density, the turbulent gas is relatively "hard", with $gamma >= 1$, at large densities, but moderately "soft", $gamma <= 0.8$, at densities below around $10^4 cm^(-3)$. At low temperatures the density probability distribution should fall ra pidly for densities larger than this value, which corresponds physically to the critical density at which collisional and radiative deexcitation rate s of HD are equal. The densities attained in turbulent protogalaxies thus depend on the relatively large deuterium abundance in our universe. We expect the same physical effect to occur in higher metallicity gas with different coolants. The case in which adiabatic (compressional) heating due to cloud collapse dominates is also discussed, and suggests a criterion for the maximum mass of Population III stars.

astro-ph↗