552 research outputs found
Outstanding intraindividual genetic diversity in fissiparous planarians (Dugesia, Platyhelminthes) with facultative sex.
Predicted genetic consequences of asexuality include high intraindividual genetic diversity (i.e., the Meselson effect) and accumulation of deleterious mutations (i.e., Mullerâs Ratchet), among others. These consequences have been largely studied in parthenogenetic organisms, but studies on fissiparous species are scarce. Differing from parthenogens, fissiparous organisms inherit part of the soma of the progenitor, including somatic mutations. Thus, in the long term, fissiparous reproduction may also result in genetic mosaicism, besides the presence of the Meselson effect and Mullerâs Ratchet. Dugesiidae planarians show outstanding regeneration capabilities, allowing them to naturally reproduce by fission, either strictly or combined with sex (facultative). Therefore, they are an ideal model to analyze the genetic footprint of fissiparous reproduction, both when it is alternated with sex and when it is the only mode of reproduction
What is there in the black box of dark energy: variable cosmological parameters or multiple (interacting) components?
The coincidence problems and other dynamical features of dark energy are
studied in cosmological models with variable cosmological parameters and in
models with the composite dark energy. It is found that many of the problems
usually considered to be cosmological coincidences can be explained or
significantly alleviated in the aforementioned models.Comment: 6 pages, 1 figure, talk given at IRGAC2006 (Barcelona, July 11-15,
2006), to appear in J. Phys.
String-Inspired Running Vacuum, the "Vacuumon", and the Swampland Criteria
We elaborate further on the compatibility of the "vacuumon potential" that
characterises the inflationary phase of the Running Vacuum Model (RVM) with the
Swampland criteria. The work is motivated by the fact that, as demonstrated
recently by the authors [1-3], the RVM framework can be derived as an effective
gravitational field theory stemming from underlying microscopic (critical)
string theory models with gravitational anomalies, involving condensation of
primordial gravitational waves. Although believed to be a classical scalar
field description, not representing a fully fledged quantum field, nonetheless
we show here that the vacuumon potential satisfies certain Swampland criteria
for the relevant regime of parameters and field range. We link the criteria to
the Gibbons-Hawking entropy that has been argued to characterise the RVM during
the de Sitter phase. These results imply that the vacuumon may, after all,
admit under certain conditions, a r\^ole as a quantum field during the
inflationary (almost de Sitter) phase of the running vacuum. The conventional
slow-roll interpretation of this field, however, fails just because it
satisfies the Swampland criteria. The RVM effective theory derived from the
low-energy effective action of string theory does, however, successfully
describe inflation thanks to the terms induced by the gravitational
anomalous condensates. In addition, the stringy version of the RVM involves the
Kalb-Ramond (KR) axion field, which, in contrast to the vacuumon, does
perfectly satisfy the slow-roll condition. We conclude that the vacuumon
description is not fully equivalent to the stringy formulation of the RVM.Comment: 37 pages revtex, 3 pdf figures incorporated; amended discussion on
running-vacuum properties and evolution in sections IVA, IVC; References
added. No effects on conclusions; version accepted for publication in
Univers
Cosmology with variable parameters and effective equation of state for Dark Energy
A cosmological constant, Lambda, is the most natural candidate to explain the
origin of the dark energy (DE) component in the Universe. However, due to
experimental evidence that the equation of state (EOS) of the DE could be
evolving with time/redshift (including the possibility that it might behave
phantom-like near our time) has led theorists to emphasize that there might be
a dynamical field (or some suitable combination of them) that could explain the
behavior of the DE. While this is of course one possibility, here we show that
there is no imperative need to invoke such dynamical fields and that a variable
cosmological constant (including perhaps a variable Newton's constant too) may
account in a natural way for all these features.Comment: LaTeX, 9 pages, 1 figure. Talk given at the 7th Intern. Workshop on
Quantum Field Theory Under the Influence of External Conditions (QFEXT 05
Cosmologies with a time dependent vacuum
The idea that the cosmological term, Lambda, should be a time dependent
quantity in cosmology is a most natural one. It is difficult to conceive an
expanding universe with a strictly constant vacuum energy density, namely one
that has remained immutable since the origin of time. A smoothly evolving
vacuum energy density that inherits its time-dependence from cosmological
functions, such as the Hubble rate or the scale factor, is not only a
qualitatively more plausible and intuitive idea, but is also suggested by
fundamental physics, in particular by quantum field theory (QFT) in curved
space-time. To implement this notion, is not strictly necessary to resort to ad
hoc scalar fields, as usually done in the literature (e.g. in quintessence
formulations and the like). A "running" Lambda term can be expected on very
similar grounds as one expects (and observes) the running of couplings and
masses with a physical energy scale in QFT. Furthermore, the experimental
evidence that the equation of state of the dark energy could be evolving with
time/redshift (including the possibility that it might currently behave
phantom-like) suggests that a time-variable Lambda term (possibly accompanied
by a variable Newton's gravitational coupling G=G(t)) could account in a
natural way for all these features. Remarkably enough, a class of these models
(the "new cosmon") could even be the clue for solving the old cosmological
constant problem, including the coincidence problem.Comment: LaTeX, 15 pages, 4 figure
Quantum anomalies in string-inspired running vacuum universe: Inflation and axion dark matter
In this letter, we elaborate further on a Cosmological 'Running-Vacuum' type model for the Universe, suggested previously by the authors [1], [2], within the context of a string-inspired effective theory in the presence of a Kalb-Ramond (KR) gravitational axion field which descends from the antisymmetric tensor of the massless gravitational string multiplet. In the presence of this field, which has anomalous CP violating interactions with the gravitons, primordial gravitational waves induce gravitational anomalies, which in turn are responsible for the appearance of H^2 and H^4 contributions to the vacuum energy density, these terms being characteristic of generic 'running-vacuum-model (RVM) type', where H is the Hubble parameter. In this work we prove in detail the appearance of the H^4 terms due to gravitational-anomaly-induced condensates in the energy density of the primordial Universe, which can self-consistently induce inflation, and subsequent exit from it, according to the generic features of RVM. We also argue in favour of the robustness of our results, which were derived within an effective low-energy field theory approach, against Ultra Violet completion of the theory. During the radiation and matter-dominated eras, gravitational anomalies cancel, as required for the consistency of the quantum matter/radiation field theory. However, chiral and QCD-axion-type anomalies survive and have important consequences for both cosmic magnetogenesis and axionic dark matter in the Universe. Finally, the stringy RVM scenario presented here predicts quintessence-like dynamical dark energy for the current Universe, which is compatible with the existing fitting analyses of such model against observations
Gravitational and chiral anomalies in the running vacuum universe and matter-antimatter asymmetry
We present a model for the Universe in which quantum anomalies are argued to play an important dual role: they are responsible for generating matter-antimatter asymmetry in the cosmos, but also provide time-dependent contributions to the vacuum energy density of 'running-vacuum' type, which drive the Universe's evolution. According to this scenario, during the inflationary phase of a string-inspired Universe, and its subsequent exit, the existence of primordial gravitational waves induces gravitational anomalies, which couple to the [Kalb-Ramond (KR)] axion field emerging from the antisymmetric tensor field of the massless gravitational multiplet of the string. Such anomalous CP-violating interactions have two important effects. First, they lead to contributions to the vacuum energy density of the form appearing in the 'running vacuum model' (RVM) framework, which are proportional to both, the square and the fourth power of the effective Hubble parameter, H2 and H4 respectively. The H4 terms may lead to inflation, in a dynamical scenario whereby the role of the inflaton is played by the effective scalar-field ('vacuumon') representation of the RVM. Second, there is an undiluted KR axion at the end of inflation, which plays an important role in generating matter-antimatter asymmetry in the cosmos, through baryogenesis via leptogenesis in models involving heavy right-handed neutrinos. As the Universe exits inflation and enters a radiation-dominated era, the generation of chiral fermionic matter is responsible for the cancellation of gravitational anomalies, thus restoring diffeomorphism invariance for the matter/radiation (quantum) theory, as required for consistency. Chiral U(1) anomalies may remain uncompensated, though, during matter/radiation dominance, providing RVM-like H2 and H4 contributions to the Universe energy density. Finally, in the current era, when the Universe enters a de Sitter phase again, and matter is no longer dominant, gravitational anomalies resurface, leading to RVM-like H2 contributions to the vacuum energy density, which are however much more suppressed, as compared to their counterparts during inflation, due to the smallness of the present era's Hubble parameter H0. In turn, this feature endows the observed dark energy with a dynamical character that follows the RVM pattern, a fact which has been shown to improve the global fits to the current cosmological observations as compared to the concordance ÎCDM model with its rigid cosmological constant, Î>0. Our model favors axionic dark matter, the source of which can be the KR axion. The uncompensated chiral anomalies in late epochs of the Universe are argued to play an important role in this, in the context of cosmological models characterized by the presence of large-scale cosmic magnetic fields at late eras
Stringy Running Vacuum Model and current Tensions in Cosmology
We discuss the potential alleviation of both the Hubble and the growth of
galactic structure data tensions observed in the current epoch of Cosmology in
the context of the so-called Stringy Running Vacuum Model (RVM) of Cosmology.
This is a gravitational field theory coupled to matter, which, at early eras,
contains gravitational (Chern-Simons (CS) type) anomalies and torsion, arising
from the fundamental degrees of freedom of the massless gravitational multiplet
of an underlying microscopic string theory. The model leads to RVM type
inflation without external inflatons, arising from the quartic powers of the
Hubble parameter that characterise the vacuum energy density due to
primordial-gravitational-wave-induced anomaly CS condensates, and dominate the
inflationary era. In modern eras, of relevance to this work, the gravitational
anomalies are cancelled by chiral matter, generated at the end of the RVM
inflationary era, but cosmic radiation and other matter fields are still
responsible for a RVM energy density with terms exhibiting a
quadratic-power-of-Hubble-parameter dependence, but also products of the latter
with logarithmic -dependencies, arising from potential quantum-gravity and
quantum-matter loop effects. In this work, such terms are examined
phenomenologically from the point of view of the potential alleviation of the
aforementioned current tensions in Cosmology. Using standard information
criteria, we find that these tensions can be substantially alleviated in a way
consistent not only with the data, but also with the underlying microscopic
theory predictions, associated with the primordial dynamical breaking of
supergravity that characterise a pre-RVM-inflationary phase of the model.Comment: 38 pages, 6 figures, 7 tables. Version accepted for publication in
Classical and Quantum Gravity. Extended discussion (new section VII),
improved Figure 6, corrected typos and references adde
String-inspired running-vacuum cosmology, quantum corrections and the current cosmological tensions
In the context of a string-inspired running vacuum model (RVM) of cosmology
with anomalies and torsion-induced axion-like fields, we discuss quantum
corrections to the corresponding energy density, in approximately de Sitter
eras, during which the Hubble parameter varies very slowly with the
cosmic time . Such corrections arise either from graviton loops in the
corresponding gravitational theory, or from path integration of massive quantum
matter fields. They depend logarithmically on , in the form , . In the modern eras, for which the terns are
dominant, such corrections may contribute to an alleviation of the currently
observed cosmological and structure-growth tensions. In particular, we
argue that such an effect is accomplished for a (dynamically-broken)
supergravity-based RVM cosmological model. In the current de-Sitter era, for
this case, rather surprisingly, the quantum graviton corrections dominate those
due to matter fields, provided the scale of the primordial (pre-RVM inflation)
dynamical breaking of local supersymmetry lies near the reduced Planck scale,
which is a natural assumption in the context of the model.Comment: 12 pages, latex (uses special (Springer Proceedings) macros), one pdf
figure incorporated; Invited plenary talk (NEM) at 40th Conference on Recent
Developments in High Energy Physics and Cosmology of the Hellenic High Energy
Physics Society (HEP2023, 5-7 April 2023, U. of Ioannina (Greece)), based
partly on e-Print:2305.15774 [gr-qc]. arXiv admin note: text overlap with
arXiv:2306.0806
- âŠ