keV Neutrino Dark Matter in a Fast Expanding Universe

We study the possibility of keV neutrino dark matter in the minimal $U(1)_{B-L}$ gauge extension of the standard model where three right handed neutrinos are automatically included due to the requirement of anomaly cancellations. Without considering extra additional particles or symmetries, we consider the lightest right handed neutrino to be in the keV mass range which is kinematically long lived. Due to gauge interactions, such a keV neutrino can be thermally produced in the early Universe followed by decoupling while being relativistic. The final relic abundance of such keV neutrino typically overclose the Universe requiring additional mechanism to bring it under observed limits. We propose a non-standard cosmological history where a scalar field $\phi$, that redshifts faster than radiation dominates the Universe prior to the radiation dominated era. We show that such a non-standard phase can keep the abundance of thermally generated keV neutrino dark matter within observed relic abundance. We constrain the non-standard phase, $U(1)_{B-L}$ parameters from these requirements and also briefly comment upon the observational aspects of such keV neutrino dark matter.Comment: 23 pages, 5 figure

Nonthermal Two Component Dark Matter Model for Fermi-LAT γ\gamma-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 $\gamma$-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 $\chi_{{}_{{}_1}}$ with $M_{\chi_{{}_{{}_1}}}\sim 125$ GeV, a moderately heavy scalar $\chi_{{}_{{}_2}}$ with $50 \,\,{\rm GeV} \leq M_{\chi_{{}_{{}_2}}}\leq 80\,\,{\rm GeV}$ and a light $\chi_{{}_{{}_3}}$ with $M_{\chi_{{}_{{}_3}}} \sim 7$ keV. There is only tiny mixing between $\chi_{{}_{{}_1}}$ and $\chi_{{}_{{}_2}}$ as well as between $\chi_{{}_{{}_1}}$ and $\chi_{{}_{{}_3}}$. 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 $\gamma$-ray excess (from the $\chi_{{}_{{}_2}} \rightarrow {\rm b} \bar{\rm b}$ decay mode) and the observation of the X-ray line (from the decay channel $\chi_{{}_{{}_3}}\rightarrow\gamma \gamma$) by the XMM-Newton observatory.Comment: 11 eps Figures, 2 Tables, 32 Pages. Minor addition in Abstract. Inclusion in Section 1 of discussion of earlier attempts to explain the concerned phenomena by astrophysical processes. Extension of discussion in Section 6 to the case of a steeper dark matter density profile. Results unchanged. Version accepted for publication in JHE

Dwarf Galaxy γ\gamma-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 $\gamma$-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 $\gamma$-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.Comment: 8 eps figures, 1 Table, 7 pages. The paper has been completely rewritten with additional references and discussions of indirect constraints from AMS-02 and ANTARES data. Basic results remain unchanged. Version accepted for publication in Europhysics Letter

Possible explanation of indirect gamma ray signatures from hidden sector fermionic dark matter

We propose the existence of a hidden or dark sector besides the standard model (SM) of particle physics, whose members (both fermionic and bosonic) obey a local SU(2)$_{\rm H}$ gauge symmetry while behaving like a singlet under the SM gauge group. However, the fermiomic fields of the dark sector also possess another global U(1)$_{\rm H}$ symmetry which remains unbroken. The local SU(2)$_{\rm H}$ invariance of the dark sector is broken spontaneously when a scalar field in this sector acquires a vacuum expectation value (VEV) and thereby generating masses to the dark gauge bosons and dark fermions charged under the SU(2)$_{\rm H}$. The lightest fermion in this dark SU(2)$_{\rm H}$ sector can be a potential dark matter candidate. We first examine the viability of the model and constrain the model parameter space by theoretical constraints such as vacuum stability and by the experimental constraints such as PLANCK limit on relic density, LHC data, limits on spin independent scattering cross-section from dark matter direct search experiments etc. We then investigate the gamma rays from the pair annihilation of the proposed dark matter candidate at the Galactic Centre region. We also extend our calculations of gamma rays flux for the case of dwarf galaxies and compare the signatures of gamma rays obtained from these astrophysical sites.Comment: 33 pages, 16 figures, title changed, major revisio

Two component WIMP-FImP dark matter model with singlet fermion, scalar and pseudo scalar

We explore a two component dark matter model with a fermion and a scalar. In this scenario the Standard Model (SM) is extended by a fermion, a scalar and an additional pseudo scalar. The fermionic component is assumed to have a global ${\rm U(1)}_{\rm DM}$ and interacts with the pseudo scalar via Yukawa interaction while a $\mathbb{Z}_2$ symmetry is imposed on the other component -- the scalar. These ensure the stability of both the dark matter components. Although the Lagrangian of the present model is CP conserving, however the CP symmetry breaks spontaneously when the pseudo scalar acquires a vacuum expectation value (VEV). The scalar component of the dark matter in the present model also develops a VEV on spontaneous breaking of the $\mathbb{Z}_2$ symmetry. Thus the various interactions of the dark sector and the SM sector are progressed through the mixing of the SM like Higgs boson, the pseudo scalar Higgs like boson and the singlet scalar boson. We show that the observed gamma ray excess from the Galactic Centre, self-interaction of dark matter from colliding clusters as well as the 3.55 keV X-ray line from Perseus, Andromeda etc. can be simultaneously explained in the present two component dark matter model.Comment: 35 pages, 5 figure

A STUDY ON STRIDE LENGTH IN INITIAL ACCELERATION PHASE FOR TRIBAL AND NON-TRIBAL SCHOOL BOYS

In India, tribal is relating to a group of people or community of people belonging to tribes. The aim of the present study was to find out average stride length in initial acceleration phases for tribal and non-tribal boys during 100m sprinting. A total of 120 boys within the age groups of 10 to 15 yrs. were selected as subject for this study. The subjects were divided into three equal sized age groups i.e., 10-11 yrs., 12-13 yrs. and 14-15 yrs. Each group was consisted of 40 subjects, among them 20 tribal boys and 20 non-tribal boys. The video graphic data was collected from 100 m performance of the subject. The data was analyzed by motional analysis software Kinovea 0.8.15 from movement of two trials of the subject. The average stride length in initial acceleration phase for tribal boys group i.e. (10-11) yrs., (12-13) yrs. and (14-15) yrs. were 200.48 cm, 220.90 cm and 228.26cm whereas non-tribal boys were 208.66 cm, 226.87 cm and 231.07 cm respectively. The stride length increased with increase of age for tribal and non-tribal of both groups. The mean values of stride length were higher for the non-tribal group of subjects than their tribal counterparts for all age groups. The difference between tribal and non-tribal boys was statistically non-significant at 0.05 levels. The average stride length in initial acceleration phase increased with increase of age for both tribal and non-tribal boys. The stride length of non-tribal boys was higher than the tribal boys for all age groups. The difference between tribal and non-tribal boys was not statistically significant. Article visualizations

Why are Women’s Self-help Groups on the Periphery of Adivasi Movements in India? Insights from Practitioners

‘Adivasi’ is an identity of protest against the oppressive practices of displacement and dispossession faced by tribal communities across India. As the social and political scenario of the vast Central Indian Plateau (CIP), the homeland of many such communities, is shaped by the social dynamics of oppression and resistance, any social or political organisation working in this region for justice and equity has to not only understand this adivasi consciousness of resistance against the concentration of capital and accumulation of surplus through a process of dispossession but also evolve their strategy in the context of adivasi consciousness. The authors have many years of experience of working with women’s group in the CIP. In this reflective piece they critique their own action as failing to assimilate the important socio-political dynamics of the adivasi consciousness. As a result the women’s groups promoted by them have remained peripheral in the struggle against dispossession. Non-inclusion of women in traditionally male dominated forums in adivasi society is a hindering factor for the women to take leading part in the adivasi movements. The authors conclude that it is important to work with both men and women to fight against dispossession which will also change the culture of male dominated committees within the Adivasi society