Measurements of σ 8 from large scale structure observations show a discordance with the extrapolated σ 8 from Planck CMB parameters using ΛCDM cosmology. Similar discordance is found in the value of H 0 and Ω m . In this paper, we show that the presence of viscosity, shear or bulk or combination of both, can remove the above mentioned conflicts simultaneously. This indicates that the data from Planck CMB observation and different LSS observations prefer small but non-zero amount of viscosity in cold dark matter fluid.

Abstract. We study the generation and evolution of magnetic field in the presence of chiral imbalance and gravitational anomaly which gives an additional contribution to the vortical current. The contribution due to gravitational anomaly is proportional to T 2 which can generate seed magnetic field irrespective of plasma being chirally charged or neutral. We estimate the order of magnitude of the magnetic field to be 10 30 G at T ∼ 10 9 GeV, with a typical length scale of the order of 10 −18 cm, which is much smaller than the Hubble radius at that temperature (10 −8 cm). Moreover, such a system possess scaling symmetry. We show that the T 2 term in the vorticity current along with scaling symmetry leads to more power transfer from lower to higher length scale as compared to only chiral anomaly without scaling symmetry.

Modulus stabilization, a must for explaining the hierarchy problem in the context of the Randall-Sundrum (RS) scenario, is traditionally achieved through the introduction of an extra field with ad hoc couplings. We point out that the stabilization can, instead, be achieved in a purely geometrodynamical way, with plausible quantum corrections in the gravity sector playing the key role. The size of the corrections that lead to acceptable phenomenology is also delineated.

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Cosmological phase transitions can be a source of Stochastic Gravitational Wave (SGW) background. Apart from the dynamics of the phase transition, the characteristic frequency and the fractional energy density Ω gw of the SGW depends upon the temperature of the transition. In this article, we compute the SGW spectrum in the light of QCD equation of state provided by the lattice results. We find that the inclusion of trace anomaly from lattice QCD, enhances the SGW signal generated during QCD phase transition by ∼ 50% and the peak frequency of the QCD era SGW are shifted higher by ∼ 25% as compared to the earlier estimates without trace anomaly. This result is extremely significant for testing the phase transition dynamics near QCD epoch.A new era of astronomy and cosmology was ushered in by the discovery of gravitational waves (GW) from merging black holes by the LIGO collaboration [1]. LIGO detectors operate in the high frequency range (10 − 10 3 ) Hz to detect sources like compact binary inspirals. In order to detect sources like massive binaries, Supernovae etc., which produces low frequency GW signal, space-based detectors such as eLISA [2], expected to operate between (10 −5 − 1) Hz, have been proposed. Furthermore, experiments like Pulsar Timing Array (PTA) [3] and Square Kilometer Array (SKA) [4,5] can measure frequency range as low as 10 −9 Hz and promise to explore the stochastic gravitational wave backgrounds. Therefore, these upcoming detectors will begin the multi-wavelength GW astronomy as a means of understanding the universe in much greater detail.On the theoretical front, modeling sources of GW signals is important. In particular, the stochastic gravitational wave background which encapsulates the information about the early universe is of great interest. It has been argued that if the cosmological phase transitions are first order and lasts for sufficiently long duration then they can be a potential source of very low frequency stochastic gravitational wave background [6][7][8][9]. Within the purview of the standard model of particle physics, at least two transitions, namely electroweak phase transition at T * ∼ 100 GeV and QCD phase transition at T * ∼ 0.1 GeV, have taken place. The former transition is associated with electroweak symmetry breaking and latter with the breaking of chiral symmetry. Although, it has been argued that the above mentioned transition proceed through a smooth crossover [10][11][12][13], there are models beyond standard model which can generate strong first order transition at electroweak [14][15][16][17][18] and QCD [19,20] scale.Recently, QCD lattice results [21] have shown that in the presence of strong interactions, the pressure p deviates from its value in the radiation dominated epoch i.e., 1/3 of the energy density ρ. This interaction measure is characterized in terms of trace anomaly and it can have interesting cosmological consequences. For instance, the prediction of Weakly Interacting Massive Particles (WIMPs) relic density differs [22] from the phenomenologic...