165 research outputs found
Crypto-unitary forms of quantum evolution operators
For the description of quantum evolution, the use of a manifestly
time-dependent quantum Hamiltonian
is shown equivalent to the work with its simplified, time-independent
alternative . A tradeoff analysis is performed recommending
the latter option. The physical unitarity requirement is shown fulfilled in a
suitable ad hoc representation of Hilbert space.Comment: 15 p
(An)Isotropic models in scalar and scalar-tensor cosmologies
We study how the constants and may vary in different
theoretical models (general relativity with a perfect fluid, scalar
cosmological models (\textquotedblleft quintessence\textquotedblright) with and
without interacting scalar and matter fields and a scalar-tensor model with a
dynamical ) in order to explain some observational results. We apply
the program outlined in section II to study three different geometries which
generalize the FRW ones, which are Bianchi \textrm{V}, \textrm{VII} and
\textrm{IX}, under the self-similarity hypothesis. We put special emphasis on
calculating exact power-law solutions which allow us to compare the different
models. In all the studied cases we arrive to the conclusion that the solutions
are isotropic and noninflationary while the cosmological constant behaves as a
positive decreasing time function (in agreement with the current observations)
and the gravitational constant behaves as a growing time function
Higher Dimensional Dark Energy Investigation with Variable and
Time variable and are studied here under a phenomenological
model of through an () dimensional analysis. The relation of
Zeldovich (1968) between and is
employed here, where is the proton mass and is Planck's constant. In
the present investigation some key issues of modern cosmology, viz. the age
problem, the amount of variation of and the nature of expansion of the
Universe have been addressed.Comment: 7 Latex pages with few change
Transverse gravity versus observations
Theories of gravity invariant under those diffeomorphisms generated by
transverse vectors, \pd_\m\xi^\m=0 are considered. Such theories are dubbed
transverse, and differ from General Relativity in that the determinant of the
metric, , is a transverse scalar. We comment on diverse ways in which these
models can be constrained using a variety of observations. Generically, an
additional scalar degree of freedom mediates the interaction, so the usual
constraints on scalar-tensor theories have to be imposed. If the purely
gravitational part is Einstein--Hilbert but the matter action is transverse,
the models predict that the three {\em a priori} different concepts of mass
(gravitational active and gravitational passive as well as inertial) are not
equivalent anymore. These transverse deviations from General Relativity are
therefore tightly constrained, actually correlated with existing bounds on
violations of the equivalence principle, local violations of Newton's third law
and/or violation of Local Position Invariance.Comment: 21 pages. Title changed. New section on Newtonian limi
Discovery of an inflated hot Jupiter around a slightly evolved star TOI-1789
Stars and planetary system
Dimensionless cosmology
Although it is well known that any consideration of the variations of
fundamental constants should be restricted to their dimensionless combinations,
the literature on variations of the gravitational constant is entirely
dimensionful. To illustrate applications of this to cosmology, we explicitly
give a dimensionless version of the parameters of the standard cosmological
model, and describe the physics of Big Bang Neucleosynthesis and recombination
in a dimensionless manner. The issue that appears to have been missed in many
studies is that in cosmology the strength of gravity is bound up in the
cosmological equations, and the epoch at which we live is a crucial part of the
model. We argue that it is useful to consider the hypothetical situation of
communicating with another civilization (with entirely different units),
comparing only dimensionless constants, in order to decide if we live in a
Universe governed by precisely the same physical laws. In this thought
experiment, we would also have to compare epochs, which can be defined by
giving the value of any {\it one} of the evolving cosmological parameters. By
setting things up carefully in this way one can avoid inconsistent results when
considering variable constants, caused by effectively fixing more than one
parameter today. We show examples of this effect by considering microwave
background anisotropies, being careful to maintain dimensionlessness
throughout. We present Fisher matrix calculations to estimate how well the fine
structure constants for electromagnetism and gravity can be determined with
future microwave background experiments. We highlight how one can be misled by
simply adding to the usual cosmological parameter set
K2-60b and K2-107b. A Sub-Jovian and a Jovian Planet from the K2 Mission
FWN – Publicaties zonder aanstelling Universiteit LeidenStars and planetary system
Qualidade de folhas e rendimento de óleo essencial em hortelã pimenta (Mentha x Piperita L.) submetida ao processo de secagem em secador de leito fixo
A new integral representation for quasi-periodic scattering problems in two dimensions
Teor e composição do óleo essencial de patchouli (Pogostemon cablin (Blanco) Benth.) após diferentes tempos de secagem em estufa e temperatura ambiente
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