27 research outputs found
Emergence of inflationary perturbations in the CSL model
The inflationary paradigm is the most successful model that explains the
observed spectrum of primordial perturbations. However, the precise emergence
of such inhomogeneities and the quantum-to-classical transition of the
perturbations has not yet reached a consensus among the community. The
Continuous Spontaneous Localization model (CSL), in the cosmological context,
might be used to provide a solution to the mentioned issues by considering a
dynamical reduction of the wave function. The CSL model has been applied to the
inflationary universe before and different conclusions have been obtained. In
this letter, we use a different approach to implement the CSL model during
inflation. In particular, in addition to accounting for the
quantum-to-classical transition, we use the CSL model to generate the
primordial perturbations, that is, the dynamical evolution provided by the CSL
model is responsible for the transition from a homogeneous and isotropic
initial state to a final one lacking such symmetries. Our approach leads to
results that can be clearly distinguished from preceding works. Specifically,
the scalar and tensor power spectra are not time-dependent, and retains the
amplification mechanism of the CSL model. Moreover, our framework depends only
on one parameter (the CSL parameter) and its value is consistent with
cosmological and laboratory observations.Comment: 14 pages. Final version. To be published in EPJ
Quasi-matter bounce and inflation in the light of the CSL model
The Continuous Spontaneous Localization (CSL) model has been proposed as a
possible solution to the quantum measurement problem by modifying the
Schr\"{o}dinger equation. In this work, we apply the CSL model to two
cosmological models of the early Universe: the matter bounce scenario and slow
roll inflation. In particular, we focus on the generation of the classical
primordial inhomogeneities and anisotropies that arise from the dynamical
evolution, provided by the CSL mechanism, of the quantum state associated to
the quantum fields. In each case, we obtained a prediction for the shape and
the parameters characterizing the primordial spectra (scalar and tensor), i.e.
the amplitude, the spectral index and the tensor-to-scalar ratio. We found that
there exist CSL parameter values, allowed by other non-cosmological
experiments, for which our predictions for the angular power spectrum of the
CMB temperature anisotropy are consistent with the best fit canonical model to
the latest data released by the Planck Collaboration.Comment: 27 pages, including 6 figures, 2 tables and one Appendix. Final
version. Accepted in EPJ
On the quantum description of the early universe
Why is it interesting to try to understand the origin of the universe?
Everything we observe today, including our existence, arose from that event.
Although we still do not have a theory that allows us to describe the origin
itself, the study of the very early era of the universe involves the ideal
terrain to analyze the interface between two of today's most successful
physical theories, General Relativity and Quantum physics. But it is also an
area in which we have a large number of observational data to test our
theoretical ideas. Two of the fathers of Quantum physics, Niels Bohr and Werner
Heisenberg, shared some thoughts that could be described with these words:
"Quantum physics tells us that there is a line between the observed and the
observer, and therefore science should be limited to what is observed. We must
give up a complete, objective and realistic theory of the world". This article
will orbit around these ideas and summarizes how it is that today, from recent
works, we are in a position to try to challenge them (at least in part) through
cosmology, seeking the quantum description of the early universe.Comment: 9 page
Novel vacuum conditions in inflationary collapse models
Within the framework of inflationary models that incorporate a spontaneous reduction of the wave function for the emergence of the seeds of cosmic structure, we study the effects on the primordial scalar power spectrum by choosing a novel initial quantum state that characterizes the perturbations of the inflaton. Specifically, we investigate under which conditions one can recover an essentially scale free spectrum of primordial inhomogeneities when the standard Bunch–Davies vacuum is replaced by another one that minimizes the renormalized stress–energy tensor via a Hadamard procedure. We think that this new prescription for selecting the vacuum state is better suited for the self-induced collapse proposal than the traditional one in the semiclassical gravity picture. We show that the parametrization for the time of collapse, considered in previous works, is maintained. Also, we obtain an angular spectrum for the CMB temperature anisotropies consistent with the one that best fits the observational data. Therefore, we conclude that the collapse mechanism might be of a more fundamental character than previously suspected.Facultad de Ciencias Astronómicas y Geofísica
Novel vacuum conditions in inflationary collapse models
Within the framework of inflationary models that incorporate a spontaneous reduction of the wave function for the emergence of the seeds of cosmic structure, we study the effects on the primordial scalar power spectrum by choosing a novel initial quantum state that characterizes the perturbations of the inflaton. Specifically, we investigate under which conditions one can recover an essentially scale free spectrum of primordial inhomogeneities when the standard Bunch–Davies vacuum is replaced by another one that minimizes the renormalized stress–energy tensor via a Hadamard procedure. We think that this new prescription for selecting the vacuum state is better suited for the self-induced collapse proposal than the traditional one in the semiclassical gravity picture. We show that the parametrization for the time of collapse, considered in previous works, is maintained. Also, we obtain an angular spectrum for the CMB temperature anisotropies consistent with the one that best fits the observational data. Therefore, we conclude that the collapse mechanism might be of a more fundamental character than previously suspected.Facultad de Ciencias Astronómicas y Geofísica
Is Planckian discreteness observable in cosmology?
A Planck scale inflationary era -- in a quantum gravity theory predicting
discreteness of quantum geometry at the fundamental scale -- produces the scale
invariant spectrum of inhomogeneities with very small tensor-to-scalar ratio of
perturbations and a hot big bang leading to a natural dark matter genesis
scenario. Here we evoke the possibility that some of the major puzzles in
cosmology would have an explanation rooted in quantum gravity
A clarification on prevailing misconceptions in unimodular gravity
The traditional presentation of Unimodular Gravity (UG) consists on
indicating that it is an alternative theory of gravity that restricts the
generic diffeomorphism invariance of General Relativity. In particular, as
often encountered in the literature, unlike General Relativity, Unimodular
Gravity is invariant solely under volume-preserving diffeomorphisms. That
characterization of UG has led to some confusion and incorrect statements in
various treatments on the subject. For instance, sometimes it is claimed
(mistakenly) that only spacetime metrics such that det
can be considered as valid solutions of the theory. Additionally, that same
(incorrect) statement is often invoked to argue that some particular gauges
(e.g. the Newtonian or synchronous gauge) are not allowed when dealing with
cosmological perturbation theory in UG. The present article is devoted to
clarify those and other misconceptions regarding the notion of diffeomorphism
invariance, in general, and its usage in the context of UG, in particular.Comment: 21 pages + Refs, 2 figure