35 research outputs found
Higgs Scalar-Tensor Theory for Gravity and the Flat Rotation Curves of Spiral Galaxies
The scalar-tensor theory of gravity with the Higgs field as scalar field is
presented. For central symmetry it reproduces the empirically measured flat
rotation curves of galaxies. We approximate the galaxy by a polytropic gas
sphere with the polytropic index and a massive core.Comment: 17 pages, 12 figure
Can induced gravity isotropize Bianchi I, V, or IX Universes?
We analyze if Bianchi I, V, and IX models in the Induced Gravity (IG) theory
can evolve to a Friedmann--Roberson--Walker (FRW) expansion due to the
non--minimal coupling of gravity and the scalar field. The analytical results
that we found for the Brans-Dicke (BD) theory are now applied to the IG theory
which has ( being the square ratio of the Higgs to
Planck mass) in a cosmological era in which the IG--potential is not
significant. We find that the isotropization mechanism crucially depends on the
value of . Its smallness also permits inflationary solutions. For the
Bianch V model inflation due to the Higgs potential takes place afterwads, and
subsequently the spontaneous symmetry breaking (SSB) ends with an effective FRW
evolution. The ordinary tests of successful cosmology are well satisfied.Comment: 24 pages, 5 figures, to be published in Phys. Rev. D1
Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes
In the weak field limit general relativity reduces, as is well known, to the
Newtonian gravitation. Alternative theories of gravity, however, do not
necessarily reduce to Newtonian gravitation; some of them, for example, reduce
to Yukawa-like potentials instead of the Newtonian potential. Since the
Newtonian gravitation is largely used to model with success the structures of
the universe, such as for example galaxies and clusters of galaxies, a way to
probe and constrain alternative theories, in the weak field limit, is to apply
them to model the structures of the universe. In the present study, we consider
how to probe Yukawa-like potentials using N-body numerical simulations.Comment: 17 pages, 11 figures. To appear in General Relativity and Gravitatio
Reconstruction of the Dark Energy equation of state
One of the main challenges of modern cosmology is to investigate the nature
of dark energy in our Universe. The properties of such a component are normally
summarised as a perfect fluid with a (potentially) time-dependent
equation-of-state parameter . We investigate the evolution of this
parameter with redshift by performing a Bayesian analysis of current
cosmological observations. We model the temporal evolution as piecewise linear
in redshift between `nodes', whose -values and redshifts are allowed to
vary. The optimal number of nodes is chosen by the Bayesian evidence. In this
way, we can both determine the complexity supported by current data and locate
any features present in . We compare this node-based reconstruction with
some previously well-studied parameterisations: the Chevallier-Polarski-Linder
(CPL), the Jassal-Bagla-Padmanabhan (JBP) and the Felice-Nesseris-Tsujikawa
(FNT). By comparing the Bayesian evidence for all of these models we find an
indication towards possible time-dependence in the dark energy
equation-of-state. It is also worth noting that the CPL and JBP models are
strongly disfavoured, whilst the FNT is just significantly disfavoured, when
compared to a simple cosmological constant . We find that our node-based
reconstruction model is slightly disfavoured with respect to the CDM
model.Comment: 17 pages, 5 figures, minor correction
Stability analysis and Observational Measurement in Chameleonic Generalised Brans--Dicke Cosmology
We investigate the dynamics of the chameleonic Generalised Brans--Dicke model
in flat FRW cosmology. In a new approach, a framework to study stability and
attractor solutions in the phase space is developed for the model by
simultaneously best fitting the stability and model parameters with the
observational data. The results show that for an accelerating universe the
phantom crossing does not occur in the past and near future.Comment: 15 pages, 18 figure
Non-minimal coupling of the scalar field and inflation
We study the prescriptions for the coupling constant of a scalar field to the
Ricci curvature of spacetime in specific gravity and scalar field theories. The
results are applied to the most popular inflationary scenarios of the universe;
their theoretical consistency and certain observational constraints are
discussed.Comment: 23 pages, LaTex, no figures, to appear in Physical Review
Towards testing the theory of gravity with DESI: summary statistics, model predictions and future simulation requirements
Large scale structure and cosmolog
DESI 2024: Constraints on Physics-Focused Aspects of Dark Energy using DESI DR1 BAO Data
International audienceBaryon acoustic oscillation data from the first year of the Dark Energy Spectroscopic Instrument (DESI) provide near percent-level precision of cosmic distances in seven bins over the redshift range -. We use this data, together with other distance probes, to constrain the cosmic expansion history using some well-motivated physical classes of dark energy. In particular, we explore three physics-focused behaviors of dark energy from the equation of state and energy density perspectives: the thawing class (matching many simple quintessence potentials), emergent class (where dark energy comes into being recently, as in phase transition models), and mirage class (where phenomenologically the distance to CMB last scattering is close to that from a cosmological constant despite dark energy dynamics). All three classes fit the data at least as well as CDM, and indeed can improve on it by to for the combination of DESI BAO with CMB and supernova data, while having one more parameter. The mirage class does essentially as well as CDM while having one less parameter. These classes of dynamical behaviors highlight worthwhile avenues for further exploration into the nature of dark energy