570 research outputs found
The phase relation between sunspot numbers and soft X-ray flares
To better understand long-term flare activity, we present a statistical study
on soft X-ray flares from May 1976 to May 2008. It is found that the smoothed
monthly peak fluxes of C-class, M-class, and X-class flares have a very
noticeable time lag of 13, 8, and 8 months in cycle 21 respectively with
respect to the smoothed monthly sunspot numbers. There is no time lag between
the sunspot numbers and M-class flares in cycle 22. However, there is a
one-month time lag for C-class flares and a one-month time lead for X-class
flares with regard to sunspot numbers in cycle 22. For cycle 23, the smoothed
monthly peak fluxes of C-class, M-class, and X-class flares have a very
noticeable time lag of one month, 5 months, and 21 months respectively with
respect to sunspot numbers. If we take the three types of flares together, the
smoothed monthly peak fluxes of soft X-ray flares have a time lag of 9 months
in cycle 21, no time lag in cycle 22 and a characteristic time lag of 5 months
in cycle 23 with respect to the smoothed monthly sunspot numbers. Furthermore,
the correlation coefficients of the smoothed monthly peak fluxes of M-class and
X-class flares and the smoothed monthly sunspot numbers are higher in cycle 22
than those in cycles 21 and 23. The correlation coefficients between the three
kinds of soft X-ray flares in cycle 22 are higher than those in cycles 21 and
23. These findings may be instructive in predicting C-class, M-class, and
X-class flares regarding sunspot numbers in the next cycle and the physical
processes of energy storage and dissipation in the corona.Comment: 8 pages, 3 figures, Accepted for publication in Astrophysics & Space
Scienc
Formation of the seed black holes: a role of quark nuggets?
Strange quark nuggets (SQNs) could be the relics of the cosmological QCD
phase transition, and they could very likely be the candidate of cold quark
matter if survived the cooling of the later Universe, although the formation
and evolution of these SQNs depend on the physical state of the hot QGP
(quark-gluon plasma) phase and the state of cold quark matter. We reconsider
the possibility of SQNs as cold dark matter, and find that the formation of
black holes in primordial halos could be significantly different from the
standard scenario. In a primordial halo, the collision between gas and SQNs
could be frequent enough, and thus the viscosity acting on each SQN would
decrease its angular momentum and make it to sink into the center of the halo,
as well as heat the gas. The SQNs with baryon numbers less than could
assemble in the center of the halo before the formation of primordial stars. A
black hole could form by merger of these SQNs, and then its mass could quickly
become about or higher, by accreting the surrounding SQNs or
gas. The black holes formed in this way could be the seeds for the supermassive
black holes at redshift as high as .Comment: 15 page
On Born approximation in black hole scattering
A massless field propagating on spherically symmetric black hole metrics such
as the Schwarzschild, Reissner-Nordstr\"{o}m and Reissner-Nordstr\"{o}m-de
Sitter backgrounds is considered. In particular, explicit formulae in terms of
transcendental functions for the scattering of massless scalar particles off
black holes are derived within a Born approximation. It is shown that the
conditions on the existence of the Born integral forbid a straightforward
extraction of the quasi normal modes using the Born approximation for the
scattering amplitude. Such a method has been used in literature. We suggest a
novel, well defined method, to extract the large imaginary part of quasinormal
modes via the Coulomb-like phase shift. Furthermore, we compare the numerically
evaluated exact scattering amplitude with the Born one to find that the
approximation is not very useful for the scattering of massless scalar,
electromagnetic as well as gravitational waves from black holes
The First Magnetic Fields
We review current ideas on the origin of galactic and extragalactic magnetic
fields. We begin by summarizing observations of magnetic fields at cosmological
redshifts and on cosmological scales. These observations translate into
constraints on the strength and scale magnetic fields must have during the
early stages of galaxy formation in order to seed the galactic dynamo. We
examine mechanisms for the generation of magnetic fields that operate prior
during inflation and during subsequent phase transitions such as electroweak
symmetry breaking and the quark-hadron phase transition. The implications of
strong primordial magnetic fields for the reionization epoch as well as the
first generation of stars is discussed in detail. The exotic, early-Universe
mechanisms are contrasted with astrophysical processes that generate fields
after recombination. For example, a Biermann-type battery can operate in a
proto-galaxy during the early stages of structure formation. Moreover, magnetic
fields in either an early generation of stars or active galactic nuclei can be
dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also
downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
Loss-of-function mutations in UDP-Glucose 6-Dehydrogenase cause recessive developmental epileptic encephalopathy
Developmental epileptic encephalopathies are devastating disorders characterized by intractable epileptic seizures and developmental delay. Here, we report an allelic series of germline recessive mutations in UGDH in 36 cases from 25 families presenting with epileptic encephalopathy with developmental delay and hypotonia. UGDH encodes an oxidoreductase that converts UDP-glucose to UDP-glucuronic acid, a key component of specific proteoglycans and glycolipids. Consistent with being loss-of-function alleles, we show using patients’ primary fibroblasts and biochemical assays, that these mutations either impair UGDH stability, oligomerization, or enzymatic activity. In vitro, patient-derived cerebral organoids are smaller with a reduced number of proliferating neuronal progenitors while mutant ugdh zebrafish do not phenocopy the human disease. Our study defines UGDH as a key player for the production of extracellular matrix components that are essential for human brain development. Based on the incidence of variants observed, UGDH mutations are likely to be a frequent cause of recessive epileptic encephalopathy
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