767 research outputs found
Distribution function approach to redshift space distortions
We develop a phase space distribution function approach to redshift space
distortions (RSD), in which the redshift space density can be written as a sum
over velocity moments of the distribution function. These moments are density
weighted and their lowest orders are density, momentum density, and stress
energy density. The series expansion is convergent on large scales. We perform
an expansion of these velocity moments into helicity modes, which are
eigenmodes under rotation around the axis of Fourier mode direction,
generalizing the scalar, vector, tensor decomposition of perturbations to an
arbitrary order. We show that only equal helicity moments correlate and derive
the angular dependence of the individual contributions to the redshift space
power spectrum in terms of angle mu between wave vector and line of sight. We
show that the dominant term of mu^2 dependence on large scales is the
cross-correlation between the density and scalar part of momentum density,
which can be related to the time derivative of the matter power spectrum.
Additional terms contributing and dominating on small scales are the vector
part of momentum density-momentum density correlations, the energy
density-density correlations, and the scalar part of anisotropic stress
density-density correlations. Similarly, we identify 7 terms contributing to
mu^4 dependence. Some of the advantages of the distribution function approach
are that the series expansion converges on large scales and remains valid in
multi-stream situations. We finish with a brief discussion of implications for
RSD in galaxies relative to dark matter, highlighting the issue of scale
dependent bias of velocity moments correlators.Comment: 12 page
Distribution function approach to redshift space distortions. Part IV: perturbation theory applied to dark matter
We develop a perturbative approach to redshift space distortions (RSD) using
the phase space distribution function approach and apply it to the dark matter
redshift space power spectrum and its moments. RSD can be written as a sum over
density weighted velocity moments correlators, with the lowest order being
density, momentum density and stress energy density. We use standard and
extended perturbation theory (PT) to determine their auto and cross
correlators, comparing them to N-body simulations. We show which of the terms
can be modeled well with the standard PT and which need additional terms that
include higher order corrections which cannot be modeled in PT. Most of these
additional terms are related to the small scale velocity dispersion effects,
the so called finger of god (FoG) effects, which affect some, but not all, of
the terms in this expansion, and which can be approximately modeled using a
simple physically motivated ansatz such as the halo model. We point out that
there are several velocity dispersions that enter into the detailed RSD
analysis with very different amplitudes, which can be approximately predicted
by the halo model. In contrast to previous models our approach systematically
includes all of the terms at a given order in PT and provides a physical
interpretation for the small scale dispersion values. We investigate RSD power
spectrum as a function of \mu, the cosine of the angle between the Fourier mode
and line of sight, focusing on the lowest order powers of \mu and multipole
moments which dominate the observable RSD power spectrum. Overall we find
considerable success in modeling many, but not all, of the terms in this
expansion.Comment: 37 pages, 13 figures, published in JCA
Exon skipping in the RET Gene encodes novel isoforms that differentially regulate RET Protein signal transduction
Rearranged during transfection (RET), a receptor tyrosine kinase that is activated by the glial cell line-derived neurotrophic factor family ligands (GFLs), plays a crucial role in the development and function of the nervous system and additionally is required for kidney development and spermatogenesis. RET encodes a transmembrane receptor that is 20 exons long and produces two known protein isoforms differing in C-terminal amino acid composition, referred to as RET9 and RET51. Studies of human pheochromocytomas identified two additional novel transcripts involving the skipping of exon 3 or exons 3, 4, and 5 and are referred to as RETΔE3 and RETΔE345, respectively. Here we report the presence of RetΔE3 and RetΔE345 in zebrafish, mice, and rats and show that these transcripts are dynamically expressed throughout development of the CNS, peripheral nervous system, and kidneys. We further explore the biochemical properties of these isoforms, demonstrating that, like full-length RET, RETΔE3 and RETΔE345 are trafficked to the cell surface, interact with all four GFRα co-receptors, and have the ability to heterodimerize with full-length RET. Signaling experiments indicate that RETΔE3 is phosphorylated in a similar manner to full-length RET. RETΔE345, in contrast, displays higher baseline autophosphorylation, specifically on the catalytic tyrosine, Tyr905, and also on one of the most important signaling residues, Tyr1062. These data provide the first evidence for a physiologic role of these isoforms in RET pathway function
On the Potts model partition function in an external field
We study the partition function of Potts model in an external (magnetic)
field, and its connections with the zero-field Potts model partition function.
Using a deletion-contraction formulation for the partition function Z for this
model, we show that it can be expanded in terms of the zero-field partition
function. We also show that Z can be written as a sum over the spanning trees,
and the spanning forests, of a graph G. Our results extend to Z the well-known
spanning tree expansion for the zero-field partition function that arises
though its connections with the Tutte polynomial
Childhood Adversity Moderates Change in Latent Patterns of Psychological Adjustment during the COVID-19 Pandemic: Results of a Survey of U.S. Adults
Emerging evidence suggests that the consequences of childhood adversity impact later psychopathology by increasing individuals’ risk of experiencing difficulties in adjusting to stressful situations later in life. The goals of this study were to: (a) identify sociodemographic factors associated with subgroups of psychological adjustment prior to and after the onset of the COVID-19 pandemic and (b) examine whether and to what extent types of childhood adversity predict transition probabilities. Participants were recruited via multiple social media platforms and listservs. Data were collected via an internet-based survey. Our analyses reflect 1942 adults (M = 39.68 years); 39.8% reported experiencing at least one form of childhood adversity. Latent profile analyses (LPAs) and latent transition analyses (LTAs) were conducted to determine patterns of psychological adjustment and the effects of childhood adversity on transition probabilities over time. We identified five subgroups of psychological adjustment characterized by symptom severity level. Participants who were younger in age and those who endorsed marginalized identities exhibited poorer psychological adjustment during the pandemic. Childhood exposure to family and community violence and having basic needs met as a child (e.g., food, shelter) significantly moderated the relation between latent profile membership over time. Clinical and research implications are discussed
Structure and function of PspA and Vipp1 N-terminal peptides: Insights into the membrane stress sensing and mitigation
The phage shock protein (Psp) response maintains integrity of the inner membrane (IM) in response to extracytoplasmic stress conditions and is widely distributed amongst enterobacteria. Its central component PspA, a member of the IM30 peripheral membrane protein family, acts as a major effector of the system through its direct association with the IM. Under non-stress conditions PspA also negatively regulates its own expression via direct interaction with the AAA + ATPase PspF. PspA has a counterpart in cyanobacteria called Vipp1, which is implicated in protection of the thylakoid membranes. PspA's and Vipp1's conserved N-terminal regions contain a putative amphipathic helix a (AHa) required for membrane binding. An adjacent amphipathic helix b (AHb) in PspA is required for imposing negative control upon PspF. Here, purified peptides derived from the putative AH regions of PspA and Vipp1 were used to directly probe their effector and regulatory functions. We observed direct membrane-binding of AHa derived peptides and an accompanying change in secondary structure from unstructured to alpha-helical establishing them as bona fide membrane-sensing AH's. The peptide-binding specificities and their effects on membrane stability depend on membrane anionic lipid content and stored curvature elastic stress, in agreement with full length PspA and Vipp1 protein functionalities. AHb of PspA inhibited the ATPase activity of PspF demonstrating its direct regulatory role. These findings provide new insight into the membrane binding and function of PspA and Vipp1 and establish that synthetic peptides can be used to probe the structure-function of the IM30 protein family
Cosmological Non-Linearities as an Effective Fluid
The universe is smooth on large scales but very inhomogeneous on small
scales. Why is the spacetime on large scales modeled to a good approximation by
the Friedmann equations? Are we sure that small-scale non-linearities do not
induce a large backreaction? Related to this, what is the effective theory that
describes the universe on large scales? In this paper we make progress in
addressing these questions. We show that the effective theory for the
long-wavelength universe behaves as a viscous fluid coupled to gravity:
integrating out short-wavelength perturbations renormalizes the homogeneous
background and introduces dissipative dynamics into the evolution of
long-wavelength perturbations. The effective fluid has small perturbations and
is characterized by a few parameters like an equation of state, a sound speed
and a viscosity parameter. These parameters can be matched to numerical
simulations or fitted from observations. We find that the backreaction of
small-scale non-linearities is very small, being suppressed by the large
hierarchy between the scale of non-linearities and the horizon scale. The
effective pressure of the fluid is always positive and much too small to
significantly affect the background evolution. Moreover, we prove that
virialized scales decouple completely from the large-scale dynamics, at all
orders in the post-Newtonian expansion. We propose that our effective theory be
used to formulate a well-defined and controlled alternative to conventional
perturbation theory, and we discuss possible observational applications.
Finally, our way of reformulating results in second-order perturbation theory
in terms of a long-wavelength effective fluid provides the opportunity to
understand non-linear effects in a simple and physically intuitive way.Comment: 84 pages, 3 figure
Results of the Search for Strange Quark Matter and Q-balls with the SLIM Experiment
The SLIM experiment at the Chacaltaya high altitude laboratory was sensitive
to nuclearites and Q-balls, which could be present in the cosmic radiation as
possible Dark Matter components. It was sensitive also to strangelets, i.e.
small lumps of Strange Quark Matter predicted at such altitudes by various
phenomenological models. The analysis of 427 m^2 of Nuclear Track Detectors
exposed for 4.22 years showed no candidate event. New upper limits on the flux
of downgoing nuclearites and Q-balls at the 90% C.L. were established. The null
result also restricts models for strangelets propagation through the Earth
atmosphere.Comment: 14 pages, 11 EPS figure
Leptogenesis from a sneutrino condensate revisited
We re--examine leptogenesis from a right--handed sneutrino condensate, paying
special attention to the term associated with the see--saw Majorana mass.
This term generates a lepton asymmetry in the condensate whose time average
vanishes. However, a net asymmetry will result if the sneutrino lifetime is not
much longer than the period of oscillations. Supersymmetry breaking by thermal
effects then yields a lepton asymmetry in the standard model sector after the
condensate decays. We explore different possibilities by taking account of both
the low--energy and Hubble terms. It will be shown that the desired baryon
asymmetry of the Universe can be obtained for a wide range of Majorana mass.Comment: 17 revtex pages, 3 figures, 1 table. Slightly modified and references
added. Final version accepted for publication in Phys. Rev.
Leptogenesis and rescattering in supersymmetric models
The observed baryon asymmetry of the Universe can be due to the
violating decay of heavy right handed (s)neutrinos. The amount of the asymmetry
depends crucially on their number density. If the (s)neutrinos are generated
thermally, in supersymmetric models there is limited parameter space leading to
enough baryons. For this reason, several alternative mechanisms have been
proposed. We discuss the nonperturbative production of sneutrino quanta by a
direct coupling to the inflaton. This production dominates over the
corresponding creation of neutrinos, and it can easily (i.e. even for a rather
small inflaton-sneutrino coupling) lead to a sufficient baryon asymmetry. We
then study the amplification of MSSM degrees of freedom, via their coupling to
the sneutrinos, during the rescattering phase which follows the nonperturbative
production. This process, which mainly influences the (MSSM) flat
directions, is very efficient as long as the sneutrinos quanta are in the
relativistic regime. The rapid amplification of the light degrees of freedom
may potentially lead to a gravitino problem. We estimate the gravitino
production by means of a perturbative calculation, discussing the regime in
which we expect it to be reliable.Comment: (20 pages, 6 figures), references added, typos corrected. Final
version in revte
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