684 research outputs found
Iceberg Motion in Lancaster Sound and Northwest Baffin Bay, Summer 1978
A radar station on Hope Monument, Devon Island, N.W.T., was operated from 7 July 1978 to 24 September 1978 to track the movement of icebergs in eastern Lancaster Sound and northwestern Baffin Bay. Data were recorded by photographing the radar screen every 20 minutes. Meteorological measurements were also made. The data were processed by computer to provide a statistical picture of the iceberg motions as well as tracks of individual bergs. The mean circulation pattern of the ice was well defined and variations about the mean did not greatly change the general form of the pattern. The dominant feature of the flow was a stream of icebergs moving with a mean speed of about 40 cm/s southward along the east coast of Devon Island from north of Philpots Island to Cape Sherard and then westward to Cape Warrender. At Cape Warrender, the bergs turned toward the centre of Lancaster Sound with directions ranging from southwest to southeast and average speeds up to 50 cm/s. East of the coastal stream in Baffin Bay, the icebergs moved slowly (<25 cm/s) westward to join the coastal stream, while south of the stream at the entrance to Lancaster Sound two large persistent eddies were observed. In Baffin Bay, variations in the flow field appeared to be in response to direct meteorological forcing while in Lancaster Sound no evidence of this response was found. The variations in iceberg motion in the sound appeared to be caused by changes in the currents.Key words: iceberg motion, radar tracking, Baffin Bay, Lancaster Soun
Relic Abundance of Asymmetric Dark Matter
We investigate the relic abundance of asymmetric Dark Matter particles that
were in thermal equilibrium in the early universe. The standard analytic
calculation of the symmetric Dark Matter is generalized to the asymmetric case.
We calculate the asymmetry required to explain the observed Dark Matter relic
abundance as a function of the annihilation cross section. We show that
introducing an asymmetry always reduces the indirect detection signal from WIMP
annihilation, although it has a larger annihilation cross section than
symmetric Dark Matter. This opens new possibilities for the construction of
realistic models of MeV Dark Matter.Comment: 20 pages, 11 figures, Accepted by JCA
Evolution of String-Wall Networks and Axionic Domain Wall Problem
We study the cosmological evolution of domain walls bounded by strings which
arise naturally in axion models. If we introduce a bias in the potential, walls
become metastable and finally disappear. We perform two dimensional lattice
simulations of domain wall networks and estimate the decay rate of domain
walls. By using the numerical results, we give a constraint for the bias
parameter and the Peccei-Quinn scale. We also discuss the possibility to probe
axion models by direct detection of gravitational waves produced by domain
walls.Comment: 19 pages, 7 figures; revised version of the manuscript, accepted for
publication in JCA
Optical, X-ray, and γ-ray observations of the candidate transitional millisecond pulsar 4FGL J0427.8-6704
We present an optical, X-ray, and γ-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary that has an associated γ-ray counterpart, 4FGL J0427.8-6704. This association has led to the source being classified as a transitional millisecond pulsar (tMSP) in an accreting state. We analyse 10.5 yr of Fermi LAT data and detect a γ-ray eclipse at the same phase as optical and X-ray eclipses at the >5 σ level, a significant improvement on the 2.8 σ level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the γ-ray source, strengthening the tMSP classification. However, analysis of several optical data sets and an X-ray observation do not reveal a change in the source’s median brightness over long time-scales or a bi-modality on short time-scales. Instead, the light curve is dominated by flickering, which has a correlation time of 2.6 min alongside a potential quasi-periodic oscillation at ∼21 min. The mass of the primary and secondary stars is constrained to be M1=1.43+0.33−0.19 M⊙ and M2=0.3+0.17−0.12 M⊙ through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the tMSP in a low accretion state classification due to the significance of the γ-ray eclipse detection
Strong, weak and flavor scalar triplets for the CDF Wjj anomaly
A model describing the 4.1\sigma\ Wjj anomaly observed by the CDF experiment
at the Tevatron collider is introduced. It features new scalar particles which
are charged both under the SU(3)_C and the SU(2)_L gauge groups and which
couple to pairs of quarks. We introduce several identical replicas of the
scalar multiplets in order to leave an unbroken U(3)_Q x U(3)_U x U(3)_D flavor
symmetry to satisfy the constraints coming from flavor physics. We discuss the
LHC reach on the new scalar resonances both in the resonant production channel
(with the Wjj final state) and in the QCD pair production channel (with the 4j
final state).Comment: 17 pages, 6 figures and 4 table
Dark Matter attempts for CoGeNT and DAMA
Recently, the CoGeNT collaboration presented a positive signal for an annual
modulation in their data set. In light of the long standing annual modulation
signal in DAMA/LIBRA, we analyze the compatibility of both of these signal
within the hypothesis of dark matter (DM) scattering on nuclei, taking into
account existing experimental constraints. We consider the cases of elastic and
inelastic scattering with either spin-dependent or spin-independent coupling to
nucleons. We allow for isospin violating interactions as well as for light
mediators. We find that there is some tension between the size of the
modulation signal and the time-integrated event excess in CoGeNT, making it
difficult to explain both simultaneously. Moreover, within the wide range of DM
interaction models considered, we do not find a simultaneous explanation of
CoGeNT and DAMA/LIBRA compatible with constraints from other experiments.
However, in certain cases part of the data can be made consistent. For example,
the modulation signal from CoGeNT becomes consistent with the total rate and
with limits from other DM searches at 90% CL (but not with the DAMA/LIBRA
signal) if DM scattering is inelastic spin-independent with just the right
couplings to protons and neutrons to reduce the scattering rate on xenon.
Conversely the DAMA/LIBRA signal (but not CoGeNT) can be explained by
spin-dependent inelastic DM scattering.Comment: 20 pages, 9 figure
Thermal inflation, baryogenesis and axions
In a previous paper, we proposed a simple extension of the Minimal
Supersymmetric Standard Model which gives rise to thermal inflation and
baryogenesis in a natural and remarkably consistent way. In this paper, we
consider the special case of our model, which is the minimal
way to incorporate a Peccei-Quinn symmetry. The axino/flatino becomes the
lightest supersymmetric particle with m_\axino \sim 1 to 10 \GeV and is
typically over-produced during the flaton decay. Interestingly though, the dark
matter abundance is minimized for m_\axino \sim 1 \GeV, to
10^{12} \GeV and |\mu| \sim 400 \GeV to 2 \TeV at an abundance coincident
with the observed abundance and with significant amounts of both axions and
axinos. Futhermore, for these values the baryon abundance naturally matches the
observed abundance.Comment: 53 pages, 20 figures. Figures reformatted, minor changes in Section
3, references adde
The CDF dijet excess from intrinsic quarks
The CDF collaboration reported an excess in the production of two jets in
association with a . We discuss constraints on possible new particle state
interpretations of this excess. The fact of no statistically significant
deviation from the SM expectation for {+dijet} events in CDF data disfavors
the new particle explanation. We show that the nucleon intrinsic strange quarks
provide an important contribution to the boson production in association
with a single top quark production. Such {+t} single top quark production
can contribute to the CDF {+dijet} excess, thus the nucleon intrinsic quarks
can provide a possible explanation to the CDF excess in {+dijet} but not in
{+dijet} events.Comment: 4 latex pages, 1 figure. Version for journal publicatio
Complementarity of the CERN Large Hadron Collider and the International Linear Collider
The next-generation high-energy facilities, the CERN Large Hadron Collider
(LHC) and the prospective International Linear Collider (ILC), are
expected to unravel new structures of matter and forces from the electroweak
scale to the TeV scale. In this report we review the complementary role of LHC
and ILC in drawing a comprehensive and high-precision picture of the mechanism
breaking the electroweak symmetries and generating mass, and the unification of
forces in the frame of supersymmetry.Comment: 14 pages, 17 figures, to be published in "Supersymmetry on the Eve of
the LHC", a special volume of European Physical Journal C, Particles and
Fields (EPJC) in memory of Julius Wes
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