84 research outputs found
Inflation driven by a holographic energy density
In this letter we study a model of inflation in which the inflationary
regimen comes from a type of holographic energy density. In particular, we
consider the Granda-Oliveros proposal for the holographic energy density, which
contains two free dimensionless parameters, and . This
holographic energy density is associated to the so-called Granda-Oliveros
infrared cutoff (G-O cutoff). Additionally, since in the inflationary regimen
the energy scales are very high, it is necessary to modify the G-O cutoff
taking into account a correction due to the ultraviolet cutoff. In this way, we
obtain an algebraic equation which implicitly includes the Hubble parameter (as
a function of e-folding number, ) and from this, we calculate the Hubble
slow-roll parameters and the values of the inflationary observables: the scalar
spectral index of the curvature perturbations and its running, the tensor
spectral index and the tensor-to-scalar ratio. Finally, since the values for
these inflationary observables are known (Planck 2018 observations), we present
constraints on the parameters and to make this a viable model.Comment: 7 pages, 2 figures, references added, minor changes, accepted for
publication in EP
Late-time cosmology in a model of modified gravity with an exponential function of the curvature
In this work, we analyse the late-time evolution of the universe for a
particular gravity model built from an exponential function of the
scalar curvature. Following the literature, we write the field equations in
terms of a suited statefinder function () and considering well
motivated physical initial conditions, the resulting equations are solved
numerically. Also, the cosmological parameters , ,
and and the statefinder quantities , , and
are explicitly expressed in terms of and its derivatives.
Furthermore, setting an appropriate set of values for the model parameters, the
cosmological parameters as well as the statefinder quantities are plotted, and
their present values (at ), are shown to be compatible with Planck 2018
observations and the CDM-model values. Considering updated
measurements from the dynamics of the expansion of the universe, , we
perform an statistical analysis to constrain the free parameters of the model,
finding a particular set of values that fit the data well and predict
acceptable values for the cosmological and statefinder parameters at present
time. Therefore, the gravity model is found to be consistent with the
considered observational data, and a viable alternative to explain the
late-time acceleration of the universe.Comment: 23 pages (in the current format), 16 figure
Cosmological constraints on a light non-thermal sterile neutrino
Although the MiniBooNE experiment has severely restricted the possible
existence of light sterile neutrinos, a few anomalies persist in oscillation
data, and the possibility of extra light species contributing as a subdominant
hot (or warm) component is still interesting. In many models, this species
would be in thermal equilibrium in the early universe and share the same
temperature as active neutrinos, but this is not necessarily the case. In this
work, we fit up-to-date cosmological data with an extended LambdaCDM model,
including light relics with a mass typically in the range 0.1 -10 eV. We
provide, first, some nearly model-independent constraints on their current
density and velocity dispersion, and second, some constraints on their mass,
assuming that they consist either in early decoupled thermal relics, or in
non-resonantly produced sterile neutrinos. Our results can be used for
constraining most particle-physics-motivated models with three active neutrinos
and one extra light species. For instance, we find that at the 3 sigma
confidence level, a sterile neutrino with mass m_s = 2 eV can be accommodated
with the data provided that it is thermally distributed with (T_s/T_nu) < 0.8,
or non-resonantly produced with (Delta N_eff) < 0.5. The bounds become
dramatically tighter when the mass increases. For m_s < 0.9 eV and at the same
confidence level, the data is still compatible with a standard thermalized
neutrino.Comment: 18 pages, 6 figure
Planning multi-terminal direct current grids based graphs theory
Transmission expansion planning in AC power systems is well known and employs a variety of optimization techniques and methodologies that have been used in recent years. By contrast, the planning of HVDC systems is a new matter for the interconnection of large power systems, and the interconnection of renewable sources in power systems. Although the HVDC systems has evolved, the first implementations were made considering only the needs of transmission of large quantities of power to be connected to the bulk AC power system. However, for the future development of HVDC systems, meshed or not, each AC system must be flexible to allow the expansion of these for future conditions. Hence, a first step for planning HVDC grids is the planning and development of multi-terminal direct current (MTDC) systems which will be later transformed in a meshed system. This paper presented a methodology that use graph theory for planning MTDC grids and for the selection of connection buses of the MTDC to an existing HVAC transmission system. The proposed methodology was applied to the Colombian case, where the obtained results permit to migrate the system from a single HVDC line to a MTDC grid
Covariant Impulse Approximation for the study of the internal structure of composite particles
We present a brief review on the Impulse Approximation method to study
processes of scattering off composite particles. We first construct the model
in a non-relativistic fashion that enables us to extend the model to a
covariant Impulse Approximation, which is needed for the study of high momentum
transfer processes.Comment: 8 Page
Evaluation of the Leggett-Garg inequality by means of the neutrino oscillations observed in reactor and accelerator experiments
We revisit the study of the violation of the Leggett-Garg inequality in
neutrino oscillation data as a mean to test some of the fundamental aspects of
quantum mechanics. In particular, we consider the results by the Daya Bay and
RENO reactor experiments, and the MINOS and NOvA accelerator experiments. We
find that DB and MINOS exhibit a strong manifestation of Leggett-Garg
violation, while for RENO and NOvA data the indication is weaker. Considering
the particular baselines and energy ranges explored by each experiment, our
results demonstrate that the Leggett-Garg violation is more evident for smaller
baseline-to-energy ratio in all the data sets considered, a relevant aspect to
be considered when searching for evidences of quantum mechanical decoherence on
neutrino oscillations.Comment: 20 pages, 13 (16) figures. Comments are welcom
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