529 research outputs found
Stochastic Processes in Yellow and Red Pulsating Variables
Random changes in pulsation period are well established in cool pulsating
stars, in particular the red giant variables: Miras, semi-regulars of types A
and B, and RV Tau variables. Such effects are also observed in a handful of
Cepheids, the SX Phe variable XX Cyg, and, most recently, the red supergiant
variable, BC Cyg, a type C semi-regular. The nature of such fluctuations is
seemingly random over a few pulsation cycles of the stars, yet the regularity
of the primary pulsation mechanism dominates over the long term. The degree of
stochasticity is linked to the dimensions of the stars, the randomness
parameter 'e' appearing to correlate closely with mean stellar radius through
the period 'P', with an average value of e/P = 0.0136+-0.0005. The physical
processes responsible for such fluctuations are uncertain, but presumably
originate in temporal modifications of envelope convection in such stars.Comment: Poster given at the "Stellar Pulsation: Challenges for Theory and
Observation" conference in Santa Fe, New Mexico (2009
Molecular Analysis Expands the Spectrum of Phenotypes Associated with GLI3 Mutations
A range of phenotypes including Greig cephalopolysyndactyly and Pallister-Hall syndromes (GCPS, PHS) are caused by pathogenic mutation of the GLI3 gene. To characterize the clinical variability of GLI3 mutations, we present a subset of a cohort of 174 probands referred for GLI3 analysis. Eighty-one probands with typical GCPS or PHS were previously reported, and we report the remaining 93 probands here. This includes 19 probands (12 mutations) who fulfilled clinical criteria for GCPS or PHS, 48 probands (16 mutations) with features of GCPS or PHS but who did not meet the clinical criteria (sub-GCPS and sub-PHS), 21 probands (6 mutations) with features of PHS or GCPS and oral-facial-digital syndrome, and 5 probands (1 mutation) with nonsyndromic polydactyly. These data support previously identified genotype-phenotype correlations and demonstrate a more variable degree of severity than previously recognized. The finding of GLI3 mutations in patients with features of oral-facial-digital syndrome supports the observation that GLI3 interacts with cilia. We conclude that the phenotypic spectrum of GLI3 mutations is broader than that encompassed by the clinical diagnostic criteria, but the genotype-phenotype correlation persists. Individuals with features of either GCPS or PHS should be screened for mutations in GLI3 even if they do not fulfill clinical criteria
Primordial magnetic fields, anomalous isocurvature fluctuations and Big Bang nucleosynthesis
We show that the presence of primordial stochastic (hypercharge) magnetic
fields before the electroweak (EW) phase transition induces isocurvature
fluctuations (baryon number inhomogeneities). Depending on the details of the
magnetic field spectrum and on the particle physics parameters (such as the
strength of the EW phase transition and electron Yukawa couplings) these
fluctuations may survive until the Big Bang nucleosynthesis (BBN). Their
lenghtscale may exceed the neutron diffusion length at that time, while their
magnitude can be so large that sizable antimatter domains are present. This
provides the possibility of a new type of initial conditions for
non-homogeneous BBN or, from a more conservative point of view, stringent
bounds on primordial magnetic fields.Comment: 4 pages, Latex, 1 epsfi
Cosmological Magnetic Fields from Primordial Helicity
Primordial magnetic fields may account for all or part of the fields observed
in galaxies. We consider the evolution of the magnetic fields created by
pseudoscalar effects in the early universe. Such processes can create
force-free fields of maximal helicity; we show that for such a field magnetic
energy inverse cascades to larger scales than it would have solely by flux
freezing and cosmic expansion. For fields generated at the electroweak phase
transition, we find that the predicted wavelength today can in principle be as
large as 10 kpc, and the field strength can be as large as 10^{-10} G.Comment: 13 page
Turning Around the Sphaleron Bound: Electroweak Baryogenesis in an Alternative Post-inflationary Cosmology
The usual sphaleron bound and the statement of the impossibility of baryon
production at a second order phase transition or analytic cross-over are
reformulated in the first part of the paper as requirements of the expansion
rate of the Universe at the electroweak scale. With an (exact or effective)
additional contribution to the energy density scaling as 1/a^6, which dominates
until just before nucleosynthesis, the observed baryon asymmetry may be
produced at the electroweak scale in simple extensions of the Minimal Standard
Model, even in the case that the phase transition is not first order. We focus
our attention on one such cosmology, in which the Universe goes through a
period termed `kination' in which its energy is dominated by the kinetic energy
of a scalar field. The required kinetic energy dominated modes can occur either
as a field rolls down an exponential (or steeper) potential, or in the
oscillation of a field about the minimum of a steep power-law potential. We
implement in detail the former case with a single exponential field first
driving inflation, and then rolling into a kinetic energy dominated mode.
Reheating is achieved using an alternative to the usual mechanism due to
Spokoiny, in which the Universe is `reheated' by particle creation in the
expanding background. Density perturbations of the magnitude required for
structure formation may also be generated. We show that the analogous model for
the power-law potential cannot be consistently implemented. In models with
inflation driven by a second field and the usual mechanism of reheating (by
decay of the inflaton) the required kinetic energy dominated cosmology is
viable in both types of potential.Comment: 44 pages, ReVTeX, with 9 postscipt figures (included); minor
modifications to figure
Speculations on Primordial Magnetic Helicity
We speculate that above or just below the electroweak phase transition
magnetic fields are generated which have a net helicity (otherwise said, a
Chern-Simons term) of order of magnitude , where is the
baryon or lepton number today. (To be more precise requires much more knowledge
of B,L-generating mechanisms than we currently have.) Electromagnetic helicity
generation is associated (indirectly) with the generation of electroweak
Chern-Simons number through B+L anomalies. This helicity, which in the early
universe is some 30 orders of magnitude greater than what would be expected
from fluctuations alone in the absence of B+L violation, should be reasonably
well-conserved through the evolution of the universe to around the times of
matter dominance and decoupling, because the early universe is an excellent
conductor. Possible consequences include early structure formation; macroscopic
manifestations of CP violation in the cosmic magnetic field (measurable at
least in principle, if not in practice); and an inverse-cascade dynamo
mechanism in which magnetic fields and helicity are unstable to transfer to
larger and larger spatial scales. We give a quasi-linear treatment of the
general-relativistic MHD inverse cascade instability, finding substantial
growth for helicity of the assumed magnitude out to scales , where is roughly the B+L to photon ratio and
is the magnetic correlation length. We also elaborate further on an
earlier proposal of the author for generation of magnetic fields above the EW
phase transition.Comment: Latex, 23 page
Microwave Background Signals from Tangled Magnetic Fields
An inhomogeneous cosmological magnetic field will create Alfven-wave modes
that induce a small rotational velocity perturbation on the last scattering
surface of the microwave background radiation. The Alfven-wave mode survives
Silk damping on much smaller scales than the compressional modes. This, in
combination with its rotational nature, ensures that there will be no sharp
cut-off in anisotropy on arc-minute scales. We estimate that a magnetic field
which redshifts to a present value of Gauss produces
temperature anisotropies at the 10 micro Kelvin level at and below 10 arc-min
scales. A tangled magnetic field, which is large enough to influence the
formation of large scale structure is therefore potentially detectable by
future observations.Comment: 5 pages, Revtex, no figure
Primordial galactic magnetic fields from domain walls at the QCD phase transition
We propose a mechanism to generate large-scale magnetic fields with
correlation lengths of 100 kpc. Domain walls with QCD scale internal structure
form and coalesce obtaining Hubble scale correlations and align nucleon spins.
Due to strong CP violation, nucleons in these walls have anomalous electric and
magnetic dipole moments and thus the walls are ferromagnetic. This induces
electromagnetic fields with Hubble size correlations. The same CP violation
also induces a maximal helicity (Chern-Simons) correlated through the Hubble
volume which supports an inverse cascade allowing the initial correlations to
grow to 100 kpc today. We estimate the generated electromagnetic fields in
terms of the QCD parameters and discuss the effects of the resulting fields.Comment: 5 pages, REVTex. Published versio
Primordial magnetic fields from inflation?
The hot plasma above the electroweak scale contains (hyper) charged scalar
particles which are coupled to Abelian gauge fields. Scalars may interact with
gravity in a non-conformally invariant way and thus their fluctuations can be
amplified during inflation. These fluctuations lead to creation of electric
currents and produce inhomogeneous distribution of charge density, resulting in
the generation of cosmological magnetic fields. We address the question whether
these fields can be coherent at large scales so that they may seed the galactic
magnetic fields. Depending upon the mass of the charged scalar and upon various
cosmological (critical fraction of energy density in matter, Hubble constant)
and particle physics parameters we found that the magnetic fields generated in
this way are much larger than vacuum fluctuations. However, their amplitude on
cosmological distances is found to be too small for seeding the galactic
magnetic fields.Comment: 32 pages in RevTex styl
Primordial Magnetic Fields and Causality
We discuss the implications of causality on a primordial magnetic field. We
show that the residual field on large scales is much more suppressed than
usually assumed and that a helical component is even more reduced. Due to this
strong suppression, even maximal primordial fields generated at the electroweak
phase transition can just marginally seed the fields in clusters, but they
cannot leave any detectable imprint on the cosmic microwave background.Comment: New version accepted for publication in JCAP, modified and improved,
conclusions unchange
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