99 research outputs found
Cosmological simulations using a static scalar-tensor theory
We present CDM -body cosmological simulations in the framework of
a static general scalar-tensor theory of gravity. Due to the influence of the
non-minimally coupled scalar field, the gravitational potential is modified by
a Yukawa type term, yielding a new structure formation dynamics. We present
some preliminary results and, in particular, we compute the density and
velocity profiles of the most massive group.Comment: 4 pages, 6 figures, to appear in Journal of Physics: Conference
Series: VII Mexican School on Gravitation and Mathematical Physics. 26
November to 1 December 2006, Playa del Carmen, Quintana Roo, Mexic
Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory
Using scaled variables we are able to integrate an equation valid for
isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD)
theory. We analyze known and new solutions for these models in relation with
the possibility that anisotropic models asymptotically isotropize, and/or
possess inflationary properties. In particular, a new solution of curve
() Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory
is analyzed.Comment: 15 pages, 4 postscript figures, to appear in Gen. Rel. Grav., special
issue dedicated in honour of Prof. H. Dehne
Non-Minimal Chaotic Inflation, Peccei-Quinn Phase Transition and non-Thermal Leptogenesis
We consider a phenomenological extension of the minimal supersymmetric
standard model (MSSM) which incorporates non-minimal chaotic inflation, driven
by a quadratic potential in conjunction with a linear term in the frame
function. Inflation is followed by a Peccei-Quinn phase transition, based on
renormalizable superpotential terms, which resolves the strong CP and mu
problems of MSSM and provide masses lower than about 10^12 GeV for the
right-handed (RH) (s)neutrinos. Baryogenesis occurs via non-thermal
leptogenesis, realized by the out-of-equilibrium decay of the RH sneutrinos
which are produced by the inflaton's decay. Confronting our scenario with the
current observational data on the inflationary observables, the light neutrino
masses, the baryon asymmetry of the universe and the gravitino limit on the
reheat temperature, we constrain the strength of the gravitational coupling to
rather large values (~45-2950) and the Dirac neutrino masses to values between
about 1 and 10 GeV.Comment: Final versio
Galactic phase transition at Ec=0.11 eV from rotation curves of cored LSB galaxies and nonperturbative dark matter mass
We analyze the a set of seventeen rotation curves of Low Surface Brightness
(LSB) galaxies from the The HI Nearby Galaxy Survey (THINGS) with different
mass models to study the core structure and to determine a phase transition
energy scale (E_c) between hot and cold dark matter, due to nonperturbative
effects in the Bound Dark Matter (BDM) model. Our results agree with previous
ones implying the cored profiles are preferred over the N-body motivated cuspy
NFW profile. We find an average galactic core radius of r_c = 260 \times
10^{+/- 1.3} pc and a phase transition energy E_c = 0.11\times 10^{+/- 0.46}
eV, that is of the same order of magnitude as the sum of the neutrino masses.Comment: 5 pages, 1 figure
Higgsflation at the GUT scale in a Higgsless Universe
We revisit inflation in induced gravity. Our focus is on models where the low
scale Planck mass is completely determined by the breaking of the scaling
symmetry in the field theory sector. The Higgs-like field which breaks the
symmetry with a GUT-scale vacuum expectation value has non-minimal couplings to
the curvature, induced by the gravitational couplings of the other light fields
in the theory, so that its expectation value controls the gravitational
strength. This field can drive inflation, and give a low energy universe in
very good agreement with the cosmological observations. The low energy dynamics
of the Standard Model cannot be unitarized by the Higgsflaton, which decouples
from the low energy theory, both because it picks up a large mass and because
its direct couplings to the low energy modes are weakened. Instead, the short
distance behavior of the Standard Model may be regulated by the dynamics of
other light degrees of freedom, such as in Higgsless models.Comment: 12 pages LaTeX, v2: takes into account the revised version of ref.
[26], v3: improved discussion of the origin of the action, version published
on PR
A spherical scalar-tensor galaxy model
We build a spherical halo model for galaxies using a general scalar-tensor
theory of gravity in its Newtonian limit. The scalar field is described by a
time-independent Klein-Gordon equation with a source that is coupled to the
standard Poisson equation of Newtonian gravity. Our model, by construction,
fits both the observed rotation velocities of stars in spirals and a typical
luminosity profile. As a result, the form of the new Newtonian potential, the
scalar field, and dark matter distribution in a galaxy are determined. Taking
into account the constraints for the fundamental parameters of the theory
(lambda,alpha), we analyze the influence of the scalar field in the dark matter
distribution, resulting in shallow density profiles in galactic centers.Comment: 14 pages, 16 plots set in 7 figures, typos and references adde
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