180 research outputs found

### 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
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### Leptogenesis by curvature coupling of heavy neutrinos

We introduce a CP violating coupling between the Ricci curvature and the
heavy right handed neutrinos. This splits the Majorana masses of the left and
the right handed heavy neutrinos. When the heavy neutrinos decay, their decay
rates are different into left and right chirality light neutrinos. A time
varying non-zero Ricci curvature can give rise to a net lepton asymmetry. The
source of a non-zero curvature in a radiation era is the quantum fluctations of
primordial fields.Comment: 13 pages. Accepted for publication in PR

### 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.

### Constraints on Covariant Horava-Lifshitz Gravity from frame-dragging experiment

The effects of Horava-Lifshitz corrections to the gravito-magnetic field are
analyzed. Solutions in the weak field, slow motion limit, referring to the
motion of a satellite around the Earth are considered. The post-newtonian
paradigm is used to evaluate constraints on the Horava-Lifshitz parameter space
from current satellite and terrestrial experiments data. In particular, we
focus on GRAVITY PROBE B, LAGEOS and the more recent LARES mission, as well as
a forthcoming terrestrial project, GINGER.Comment: 14 pages, 1 figur

### Quantization of Scalar Fields in Curved Background and Quantum Algebras

We show that a suitable deformation of the algebra $h_k(1)$ of the creation
and annihilation operators for a complex scalar field, initially quantized in
Minkowski space--time, induces the canonical quantization of the same field in
a generic gravitational background. This discloses the physical meaning of the
deformation parameter $q$ which turns out to be related to the gravitational
field. The thermal properties are re-obtained in this formalism, and the
application to Schwarzschild and Rindler space-times are carried out.Comment: 20 pages, Revte

### 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

### 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

### Primordial magnetic fields and gravitational baryogenesis in nonlinear electrodynamics

The amplification of the primordial magnetic fields and the gravitational
baryogenesis, a mechanism that allows to generate the baryon asymmetry in the
Universe by means of the coupling between the Ricci scalar curvature and the
baryon current, are reviewed in the framework of the nonlinear electrodynamics.
To study the amplification of the primordial magnetic field strength, we write
down the gauge invariant wave equations and then solve them (in the long
wavelength approximation) for three different eras of the Universe: de Sitter,
the reheating and the radiation dominated era. Constraints on parameters
entering the nonlinear electrodynamics are obtained by using the amplitude of
the observed galactic magnetic fields and the baryon asymmetry, which are
characterized by the dimensionless parameters $r\sim 10^{-37}$ and
$\eta_B\lesssim 9\times 10^{-11}$, respectively.Comment: 10 pages, 3 tables, 6 figures. Accepted for publication in Physical
Review

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