297 research outputs found
Instant preheating mechanism and UHECR
Top-down models assume that the still unexplained Ultra High Energy Cosmic
Rays (UHECR's) are the decay products of superheavy particles. Such particles
may have been produced by one of the post-inflationary reheating mechanisms and
may account for a fraction of the cold dark matter. In this paper, we assess
the phenomenological applicability of the simplest instant preheating framework
not to describe a reheating process, but as a mechanism to generate relic
supermassive particles as possible sources of UHECR's. We use cosmic ray flux
and cold dark matter observational data to constrain the parameters of the
model.Comment: 7 pages, 2 figures, submitted to PR
Timing of insemination and fertility in dairy and beef cattle receiving timed artificial insemination using sex-sorted sperm
AbstractThe objective was to evaluate the effects of timing of insemination and type of semen in cattle subjected to timed artificial insemination (TAI). In Experiment 1, 420 cyclic Jersey heifers were bred at either 54 or 60 h after P4-device removal, using either sex-sorted (2.1 × 106 sperm/straw) or non-sorted sperm (20 × 106 sperm/straw) from three sires (2 × 2 factorial design). There was an interaction (P = 0.06) between time of AI and type of semen on pregnancy per AI (P/AI, at 30 to 42 d after TAI); it was greater when sex-sorted sperm (P < 0.01) was used at 60 h (31.4%; 32/102) than at 54 h (16.2%; 17/105). In contrast, altering the timing of AI did not affect conception results with non-sorted sperm (54 h = 50.5%; 51/101 versus 60 h = 51.8%; 58/112; P = 0.95). There was an effect of sire (P < 0.01) on P/AI, but no interaction between sire and time of AI (P = 0.88). In Experiment 2, 389 suckled Bos indicus beef cows were enrolled in the same treatment groups used in Experiment 1. Sex-sorted sperm resulted in lower P/AI (41.8%; 82/196; P = 0.05) than non-sorted sperm (51.8%; 100/193). In addition, there was a tendency for greater P/AI (P = 0.11) when TAI was performed 60 h (50.8%; 99/195) versus 54 h (42.8%; 83/194) after removing the progestin implant. In Experiment 3, 339 suckled B. indicus cows were randomly assigned to receive TAI with sex-sorted sperm at 36, 48, or 60 h after P4 device removal. Ultrasonographic examinations were performed twice daily in all cows to confirm ovulation. On average, ovulation occured 71.8 ± 7.8 h after P4 removal, and greater P/AI was achieved when insemination was performed closer to ovulation. The P/AI was greatest (37.9%) for TAI performed between 0 and 12 h before ovulation, whereas P/AI was significantly less for TAI performed between 12.1 and 24 h (19.4%) or >24 h (5.8%) before ovulation. In conclusion, sex-sorted sperm resulted in a lesser P/AI than non-sorted sperm following TAI. However, improvements in P/AI with delayed time of AI were possible (Experiments 1 and 3), and seemed achievable when breeding at 60 h following progestin implant removal, compared to the standard 54 h normally used in TAI protocols
Back reaction in the formation of a straight cosmic string
A simple model for the formation of a straight cosmic string, wiggly or
unperturbed is considered. The gravitational field of such string is computed
in the linear approximation. The vacuum expectation value of the stress tensor
of a massless scalar quantum field coupled to the string gravitational field is
computed to the one loop order. Finally, the back-reaction effect on the
gravitational field of the string is obtained by solving perturbatively the
semiclassical Einstein's equations.Comment: 29 pages, LaTeX, no figures. A postcript version can be obtained from
anonymous ftp at ftp://ftp.ifae.es/preprint.f
Modified iterative versus Laplacian Landau gauge in compact U(1) theory
Compact U(1) theory in 4 dimensions is used to compare the modified iterative
and the Laplacian fixing to lattice Landau gauge in a controlled setting, since
in the Coulomb phase the lattice theory must reproduce the perturbative
prediction. It turns out that on either side of the phase transition clear
differences show up and in the Coulomb phase the ability to remove double Dirac
sheets proves vital on a small lattice.Comment: 14 pages, 8 figures containing 23 graphs, v2: 2 figures removed, 2
references adde
Simple Dynamics on the Brane
We apply methods of dynamical systems to study the behaviour of the
Randall-Sundrum models. We determine evolutionary paths for all possible
initial conditions in a 2-dimensional phase space and we investigate the set of
accelerated models. The simplicity of our formulation in comparison to some
earlier studies is expressed in the following: our dynamical system is a
2-dimensional Hamiltonian system, and what is more advantageous, it is free
from the degeneracy of critical points so that the system is structurally
stable. The phase plane analysis of Randall-Sundrum models with isotropic
Friedmann geometry clearly shows that qualitatively we deal with the same types
of evolution as in general relativity, although quantitatively there are
important differences.Comment: an improved version, 34 pages, 9 eps figure
Inflation and late time acceleration in braneworld cosmological models with varying brane tension
Braneworld models with variable brane tension introduce a new
degree of freedom that allows for evolving gravitational and cosmological
constants, the latter being a natural candidate for dark energy. We consider a
thermodynamic interpretation of the varying brane tension models, by showing
that the field equations with variable can be interpreted as
describing matter creation in a cosmological framework. The particle creation
rate is determined by the variation rate of the brane tension, as well as by
the brane-bulk energy-matter transfer rate. We investigate the effect of a
variable brane tension on the cosmological evolution of the Universe, in the
framework of a particular model in which the brane tension is an exponentially
dependent function of the scale factor. The resulting cosmology shows the
presence of an initial inflationary expansion, followed by a decelerating
phase, and by a smooth transition towards a late accelerated de Sitter type
expansion. The varying brane tension is also responsible for the generation of
the matter in the Universe (reheating period). The physical constraints on the
model parameters, resulted from the observational cosmological data, are also
investigated.Comment: 25 pages, 8 figures, accepted for publication in European Physical
Journal
Particle creation, classicality and related issues in quantum field theory: II. Examples from field theory
We adopt the general formalism, which was developed in Paper I
(arXiv:0708.1233) to analyze the evolution of a quantized time-dependent
oscillator, to address several questions in the context of quantum field theory
in time dependent external backgrounds. In particular, we study the question of
emergence of classicality in terms of the phase space evolution and its
relation to particle production, and clarify some conceptual issues. We
consider a quantized scalar field evolving in a constant electric field and in
FRW spacetimes which illustrate the two extreme cases of late time adiabatic
and highly non-adiabatic evolution. Using the time-dependent generalizations of
various quantities like particle number density, effective Lagrangian etc.
introduced in Paper I, we contrast the evolution in these two limits bringing
out key differences between the Schwinger effect and evolution in the de Sitter
background. Further, our examples suggest that the notion of classicality is
multifaceted and any one single criterion may not have universal applicability.
For example, the peaking of the phase space Wigner distribution on the
classical trajectory \emph{alone} does not imply transition to classical
behavior. An analysis of the behavior of the \emph{classicality parameter},
which was introduced in Paper I, leads to the conclusion that strong particle
production is necessary for the quantum state to become highly correlated in
phase space at late times.Comment: RevTeX 4; 27 pages; 18 figures; second of a series of two papers, the
first being arXiv:0708.1233 [gr-qc]; high resolution figures available from
the authors on reques
Particle creation, classicality and related issues in quantum field theory: I. Formalism and toy models
The quantum theory of a harmonic oscillator with a time dependent frequency
arises in several important physical problems, especially in the study of
quantum field theory in an external background. While the mathematics of this
system is straightforward, several conceptual issues arise in such a study. We
present a general formalism to address some of the conceptual issues like the
emergence of classicality, definition of particle content, back reaction etc.
In particular, we parametrize the wave function in terms of a complex number
(which we call excitation parameter) and express all physically relevant
quantities in terms it. Many of the notions -- like those of particle number
density, effective Lagrangian etc., which are usually defined using asymptotic
in-out states -- are generalized as time-dependent concepts and we show that
these generalized definitions lead to useful and reasonable results. Having
developed the general formalism we apply it to several examples. Exact analytic
expressions are found for a particular toy model and approximate analytic
solutions are obtained in the extreme cases of adiabatic and highly
non-adiabatic evolution. We then work out the exact results numerically for a
variety of models and compare them with the analytic results and
approximations. The formalism is useful in addressing the question of emergence
of classicality of the quantum state, its relation to particle production and
to clarify several conceptual issues related to this. In Paper II
(arXiv:0708.1237), which is a sequel to this, the formalism will be applied to
analyze the corresponding issues in the context of quantum field theory in
background cosmological models and electric fields.Comment: RevTeX 4; 32 pages; 28 figures; first of a series of two papers, the
second being arXiv:0708.1237 [gr-qc]; high resolution figures available from
the authors on reques
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
TRIB1 regulates tumor growth via controlling tumor-associated macrophage phenotypes and is associated with breast cancer survival and treatment response
Methods: Bioinformatic analysis was used to investigate the link between TRIB1 expression in breast cancer and therapeutic response to chemotherapy. In vivo models of breast cancer included immune-competent mice to characterize the consequences of altered (reduced or elevated) myeloid Trib1 expression on tumor growth and composition of stromal immune cell populations.
Results: TRIB1 was highly expressed by TAMs in breast cancer and high TRIB1 expression correlated with response to chemotherapy and patient survival. Both overexpression and knockout of myeloid Trib1 promote mouse breast tumor growth, albeit through different molecular mechanisms. Myeloid Trib1 deficiency led to an early acceleration of tumor growth, paired with a selective reduction in perivascular macrophage numbers in vivo and enhanced oncogenic cytokine expression in vitro. In contrast, elevated levels of Trib1 in myeloid cells led to an increased late-stage mammary tumor volume, coupled with a reduction of NOS2 expressing macrophages and an overall reduction of macrophages in hypoxic tumor regions. In addition, we show that myeloid Trib1 is a previously unknown, negative regulator of the anti-tumor cytokine IL-15, and that increased myeloid Trib1 expression leads to reduced IL-15 levels in mammary tumors, with a consequent reduction in the number of T-cells that are key to anti-tumor immune responses.
Conclusions: Together, these results define a key role for TRIB1 in chemotherapy responses for human breast cancer and provide a mechanistic understanding for the importance of the control of myeloid TRIB1 expression in the development of this disease
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