1,056 research outputs found
Accretion regimes in the X-ray pulsar 4U 1901+03
The source 4U 1901+03 is a high-mass X-ray pulsar than went into outburst in
2003. Observation performed with the Rossi X-ray Timing Explorer showed
spectral and timing variability, including the detection of flares,
quasi-periodic oscillations, complex changes in the pulse profiles, and pulse
phase dependent spectral variability. We re-analysed the data covering the 2003
X-ray outburst and focused on several aspects of the variability that have not
been discussed so far. These are the 10 keV feature and the X-ray spectral
states and their association with accretion regimes, including the transit to
the propeller state at the end of the outburst. We find that 4U 1901+03 went
through three accretion regimes over the course of the X-ray outburst. At the
peak of the outburst and for a very short time, the X-ray flux may have
overcome the critical limit that marks the formation of a radiative shock at a
certain distance above the neutron star surface. Most of the time, however, the
source is in the subcritical regime. Only at the end of the outburst, when the
luminosity decreased below ~10^{36} (d/10 kpc)^2 erg/s, did the source enter
the propeller regime. Evidence for the existence of these regimes comes from
the pulse profiles, the shape of the hardness-intensity diagram, and the
correlation of various spectral parameters with the flux. The 10 keV feature
appears to strongly depend on the X-ray flux and on the pulse phase, which
opens the possibility to interpret this feature as a cyclotron line.Comment: accepted for publication in A&A. arXiv admin note: text overlap with
arXiv:astro-ph/9704084 by other author
SO(3) family symmetry and axions
Motivated by the idea of comprehensive unification, we study a gauged SO(3)
flavor extension of the extended Standard Model, including right-handed
neutrinos and a Peccei-Quinn symmetry with simple charge assignments. The model
accommodates the observed fermion masses and mixings and yields a
characteristic, successful relation among them. The Peccei-Quinn symmetry is an
essential ingredient.Comment: 9 pages, matches published versio
Light majoron cold dark matter from topological defects and the formation of boson stars
We show that for a relatively light majoron ( eV) non-thermal
production from topological defects is an efficient production mechanism.
Taking the type I seesaw as benchmark scheme, we estimate the primordial
majoron abundance and determine the required parameter choices where it can
account for the observed cosmological dark matter. The latter is consistent
with the scale of unification. Possible direct detection of light majorons with
future experiments such as PTOLEMY and the formation of boson stars from the
majoron dark matter are also discussed.Comment: 27 pages, 3 figures; v2: references added, matches published versio
Three-family left-right symmetry with low-scale seesaw mechanism
We suggest a new left-right symmetric model implementing a low-scale seesaw
mechanism in which quantum consistency requires three families of fermions. The
symmetry breaking route to the Standard Model determines the profile of the
"next" expected new physics, characterized either by the simplest left-right
gauge symmetry or by the 3-3-1 scenario. The resulting gauge bosons
can be probed at the LHC and provide a production portal for the right-handed
neutrinos. On the other hand, its flavor changing interactions would affect the
K, D and B neutral meson systems.Comment: 10 pages, 2 figures. Revised version as accepted by JHE
Spectroscopy of the brightest optical counterparts of X-ray sources in the direction of M~31 and M~33
Recent surveys of the Local Group spiral Galaxies M31 and M33 with XMM-Newton
yielded a large number of X-ray sources. As part of the effort to identify and
classify the objects responsible for this X-ray emission, we have obtained
optical spectra of the brightest optical counterparts of the identified X-ray
sources, using the 1.3m Skinakas Telescope. Most of these objects are
foreground star candidates. The purpose of the present study is to confirm this
identification and to explore the compatibility between the optical spectral
classification and the observed X-ray properties of the sources. We have
obtained optical spectra for the 14 brightest optical counterparts of X-ray
sources identified by XMM-Newton in the direction of M31 and for 21 optical
counterparts in the direction of M33, using the 1.3m Skinakas telescope in
Crete, Greece. All of the M31 sources and all but one of the M33 sources were
confirmed to be foreground stars, of spectral types between A and M. One of the
stars is a late M dwarf with H-alpha emission, a flare star, also displaying
strong X-ray variability. One of the M~33 sources (lying within the D25
ellipse) corresponds to a previously known background galaxy, LEDA 5899.Comment: 9 pages, 12 figures, accepted in A&
Bound-state dark matter with Majorana neutrinos
We propose a simple scenario in which dark matter (DM) emerges as a stable
neutral hadronic thermal relics, its stability following from an exact
symmetry. Neutrinos pick up radiatively induced
Majorana masses from the exchange of colored DM constituents. There is a common
origin for both dark matter and neutrino mass, with a lower bound for
neutrinoless double beta decay. Direct DM searches at nuclear recoil
experiments will test the proposal, which may also lead to other
phenomenological signals at future hadron collider and lepton flavour violation
experiments.Comment: 9 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1803.0852
A Model of Comprehensive Unification
Comprehensive - that is, gauge and family - unification using spinors has
many attractive features, but it has been challenged to explain chirality.
Here, by combining an orbifold construction with more traditional ideas, we
address that difficulty. Our candidate model features three chiral families and
leads to an acceptable result for quantitative unification of couplings. A
potential target for accelerator and astronomical searches emerges.Comment: 5 pages, 2 figures. Published versio
Spontaneous Breaking of Lepton Number and Cosmological Domain Wall Problem
We show that if global lepton number symmetry is spontaneously broken in a
post inflation epoch, then it can lead to the formation of cosmological domain
walls. This happens in the well-known "Majoron paradigm" for neutrino mass
generation. We propose some realistic examples which allow spontaneous lepton
number breaking to be safe from such domain walls.Comment: 8 pages, References added, Discussion on Domain Wall Problem
Expanded, Conclusions Unchanged, Version Published in Phys. Rev. Let
The role of the inflammasome in cellular responses to toxins and bacterial effectors
Invading pathogens are recognized by mammalian cells through dedicated receptors found either at the cell surface or in the cytoplasm. These receptors, like the trans-membrane Toll-like Receptors (TLR) or the cytosolic Nod-like Receptors (NLR), initiate innate immunity after recognition of molecular patterns found in bacteria or viruses, such as LPS, flagellin, or double-stranded RNA. Recognition of molecules produced only by a specific pathogen, such as a viral envelop protein or a bacterial adhesin does not appear to occur. Bacterial protein toxins, however, might compose an intermediate class. Considering the diversity of toxins in terms of structure, it is unlikely that cells respond to them via specific molecular recognition. It rather appears that different classes of toxins trigger cellular changes that are sensed by the cells as danger signals, such as changes in cellular ion composition after membrane perforation by pore-forming toxins or type III secretion systems. The signaling pathways triggered through toxin-induced cell alterations will likely play a role in modulating host responses to virulent bacteria. We will here describe the few studied cases in which detection of the toxin by the host cell was addressed. The review will include not only toxins but also bacteria effectors secreted by the bacterium in to the host cell cytoplas
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