Matter-Antimatter Asymmetry Generated by Loop Quantum Gravity

We show that Loop Quantum Gravity provides new mechanisms through which observed matter-antimatter asymmetry in the Universe can naturally arise at temperatures less than GUT scale. This is enabled through the introduction of a new length scale ${\cal L}$, much greater than Planck length ($l_P$), to obtain semi-classical weave states in the theory. This scale which depends on the momentum of the particle modifies the dispersion relation for different helicities of fermions and leads to lepton asymmetry.Comment: To appear in Phys. Lett. B. Minor changes in presentation. References adde

The emission of Gamma Ray Bursts as a test-bed for modified gravity

The extreme physical conditions of Gamma Ray Bursts can constitute a useful observational laboratory to test theories of gravity where very high curvature regimes are involved. Here we propose a sort of curvature engine capable, in principle, of explaining the huge energy emission of Gamma Ray Bursts. Specifically, we investigate the emission of radiation by charged particles non-minimally coupled to the gravitational background where higher order curvature invariants are present. The coupling gives rise to an additional force inducing a non-geodesics motion of particles. This fact allows a strong emission of radiation by gravitationally accelerated particles. As we will show with some specific model, the energy emission is of the same order of magnitude of that characterizing the Gamma Ray Burst physics. Alternatively, strong curvature regimes can be considered as a natural mechanism for the generation of highly energetic astrophysical events. Possible applications to cosmology are discussed.Comment: 4 pages, 1 figure, accepted for publication in Phys. Lett.

Dark energy from Neutrinos and Standard Model Higgs potential

If neutrino mass is a function of the Higgs potential then minimum of the total thermodynamic potential $\Omega$ (which is the Higgs potential minus the neutrino pressure) can shift from the standard electro-weak vev $v=246.2$ GeV by a small amount which depends on the neutrino pressure. If the neutrino mass is a very steep function of the Higgs field then the equilibrium thermodynamic potential can act like the dark energy with $\omega \simeq -1$. Choosing the neutrino mass as logarithmic function of the Higgs field and a heavy mass scale, we find that the correct magnitude of the cosmological density of the present universe $\rho_\lambda \simeq (0.002 eV)^4$ is obtained by choosing the heavy mass at the GUT scale.Comment: 12 page

Constraints on NonCommutative Spectral Action from Gravity Probe B and Torsion Balance Experiments

Noncommutative spectral geometry offers a purely geometric explanation for the standard model of strong and electroweak interactions, including a geometric explanation for the origin of the Higgs field. Within this framework, the gravitational, the electroweak and the strong forces are all described as purely gravitational forces on a unified noncommutative space-time. In this study, we infer a constraint on one of the three free parameters of the model, namely the one characterising the coupling constants at unification, by linearising the field equations in the limit of weak gravitational fields generated by a rotating gravitational source, and by making use of recent experimental data. In particular, using data obtained by Gravity Probe B, we set a lower bound on the Weyl term appearing in the noncommutative spectral action, namely $\beta \gtrsim 10^{-6}$m$^{-1}$. This constraint becomes stronger once we use results from torsion balance experiments, leading to $\beta \gtrsim 10^{4}$m$^{-1}$. The latter is much stronger than any constraint imposed so far to curvature squared terms.Comment: 12 page

Thermal condensate structure and cosmological energy density of the Universe

The aim of this paper is the study of thermal vacuum condensate for scalar and fermion fields. We analyze the thermal states at the temperature of the cosmic microwave background (CMB) and we show that the vacuum expectation value of the energy momentum tensor density of photon fields reproduces the energy density and pressure of the CMB. We perform the computations in the formal framework of the thermo field dynamics. We also consider the case of neutrinos and thermal states at the temperature of the neutrino cosmic background. Consistency with the estimated lower bound of the sum of the active neutrino masses is verified. In the boson sector, non trivial contribution to the energy of the universe is given by particles of masses of the order of $10^{-4}eV$ compatible with the ones of the axion-like particles. The fractal self-similar structure of the thermal radiation is also discussed and related to the coherent structure of the thermal vacuum.Comment: 5 page