Chiral plasma instability and primordial Gravitational wave

It is known that cosmic magnetic field, if present, can generate anisotropic stress in the plasma and hence, can act as a source of gravitational waves. These cosmic magnetic fields can be generated at very high temperature, much above electroweak scale, due to the gravitational anomaly in presence of the chiral asymmetry. The chiral asymmetry leads to instability in the plasma which ultimately leads to the generation of magnetic fields. In this article, we discuss the generation of gravitational waves, during the period of instability, in the chiral plasma sourced by the magnetic field created due to the gravitational anomaly. We have shown that such gravitational wave will have a unique spectrum. Moreover, depending on the temperature of the universe at the time of its generation, such gravitational waves can have a wide range of frequencies. We also estimate the amplitude and frequency of the gravitational waves and delineate the possibility of its detection by future experiments like eLISA.Comment: 8 pages, 2 figure

Bounds on Neutrino Mass in Viscous Cosmology

Effective field theory of dark matter fluid on large scales predicts the presence of viscosity of the order of $10^{-6} H_0 M_P^2$. It has been shown that this magnitude of viscosities can resolve the discordance between large scale structure observations and Planck CMB data in the $\sigma_8$-$\Omega_m^0$ and $H_0$-$\Omega_m^0$ parameters space. Massive neutrinos suppresses the matter power spectrum on the small length scales similar to the viscosities. We show that by including the effective viscosity, which arises from summing over non linear perturbations at small length scales, severely constrains the cosmological bound on neutrino masses. Under a joint analysis of Planck CMB and different large scale observation data, we find that upper bound on the sum of the neutrino masses at 2-$\sigma$ level, decreases from $\sum m_\nu \le 0.396\,$eV (normal hierarchy) and $\sum m_\nu \le 0.378 \,$eV (inverted hierarchy) to $\sum m_\nu \le 0.267\,$eV (normal hierarchy) and $\sum m_\nu \le 0.146\,$eV (inverted hierarchy) when the effective viscosities are included.Comment: 19 pages, 13 figure

Chiral Battery, scaling laws and magnetic fields

by Sampurn Anand, Jitesh R. Bhatt and Arun Kumar Pande

Bounds on neutrino mass in viscous cosmology

Effective field theoretic description of dark matter fluid on large scales predicts viscosity of the order 10−6 H0 MP2. Recently, it has been shown that the same magnitude of viscosity can resolve the discordance between large scale structure observations and Planck CMB data in the σ8-Ωm0 and H0-Ωm0 parameters space. On the other hand, massive neutrinos suppresses the matter power spectrum on the small length scales similar to the viscosities. Therefore, it is expected that the viscous dark matter setup along with massive neutrinos can provide stringent constraint on neutrino mass. In this article, we show that the inclusion of effective viscosity, which arises from summing over non linear perturbations at small length scales, indeed severely constrains the cosmological bound on neutrino masses. Under a joint analysis of Planck CMB and different large scale observation data, we find that upper bound on the sum of the neutrino masses, at 2-σ level, decreases respectively from ∑ mν ≤ 0.396 eV (for normal hierarchy) and ∑ mν ≤ 0.378 eV (for inverted hierarchy) to ∑ mν ≤ 0.267 eV (for normal hierarchy) and ∑ mν ≤ 0.146 eV (for inverted hierarchy).by Sampurn Ananda, Prakrut Chaubala, Arindam Mazumdara, Subhendra Mohantya and Priyank Parashari

σ8 Discrepancy and its solutions

In the recent past, measurements of ?8 from large scale structure observations have shown some discordance with its value obtained from Planck CMB within the ? CDM frame. This discordance naturally leads to a mismatch in the value of H0 also. Under the presumption that these discordances are not due to systematics, several attempts have been made to ameliorate the tensions. In this article, we describe the methods of determination of ?8 from large scale as well as CMB observations. We discuss that these discrepancies vanish if we consider the energy momentum tensor for an imperfect fluid which could arise due to self-interaction of dark matter or in an effective description of large scale structure. We demonstrate how the presence of viscosities in cold dark fluid on large scales ameliorate the problem elegantly than other solutions. We also estimate the neutrino mass in the viscous cosmological setup.by Subhendra Mohanty, Sampurn Anand, PrakrutChaubal, Arindam Mazumdar and Priyank Parashar