6,153 research outputs found
Interpretation of the unprecedentedly long-lived high-energy emission of GRB 130427A
High energy photons (>100 MeV) are detected by the Fermi/LAT from GRB 130427A
up to almost one day after the burst, with an extra hard spectral component
being discovered in the high-energy afterglow. We show that this hard spectral
component arises from afterglow synchrotron-self Compton emission. This
scenario can explain the origin of >10 GeV photons detected up to ~30000s after
the burst, which would be difficult to be explained by synchrotron radiation
due to the limited maximum synchrotron photon energy. The lower energy
multi-wavelength afterglow data can be fitted simultaneously by the afterglow
synchrotron emission. The implication of detecting the SSC emission for the
circumburst environment is discussed.Comment: 4 pages, 2 figures, ApJL in pres
Three-body interactions on a triangular lattice
We analyze the hard-core Bose-Hubbard model with both the three-body and
nearest neighbor repulsions on the triangular lattice. The phase diagram is
achieved by means of the semi-classical approximation and the quantum Monte
Carlo simulation. For a system with only the three-body interactions, both the
supersolid phase and one third solid disappear while the two thirds solid
stably exists. As the thermal behavior of the bosons with nearest neighbor
repulsion, the solid and the superfluid undergo the 3-state Potts and the
Kosterlitz-Thouless type phase transitions, respectively. In a system with both
the frustrated nearest neighbor two-body and three-body interactions, the
supersolid and one third solid revive. By tuning the strength of the three-body
interactions, the phase diagram is distorted, because the one-third solid and
the supersolid are suppressed.Comment: 6 pages, 11 figure
Static impurities in a supersolid of interacting hard-core bosons on a triangular lattice
We study the effect of impurities in a supersolid phase in comparison to the
behavior in the solid and superfluid phases. A supersolid phase has been
established for interacting hardcore bosons on a triangular lattice which may
be realizable by ultracold atomic gases. Static vacancies are considered in
this model which always lower the magnitude of the order parameter in the solid
or superfluid phases. In the supersolid phase, however, the impurities directly
affect both order parameters simultaneously and thereby reveal an interesting
interplay between them. In particular the solid order may be enhanced at the
cost of a strong reduction of the superfluidity, which shows that the two order
parameters cannot be in a simple superposition. We also observe an unusual
impurity pinning effect in the solid ordered phase, which results in two
distinct states separated by a first-order transition.Comment: 5 pages, 5 figures, final version. More information at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Fourth generation Majorana neutrino, dark matter and Higgs physics
We consider extensions of the standard model with fourth generation fermions
(SM4) in which extra symmetries are introduced such that the transitions
between the fourth generation fermions and the ones in the first three
generations are forbidden. In these models, the stringent lower bounds on the
masses of fourth generation quarks from direct searches are relaxed, and the
lightest fourth neutrino is allowed to be stable and light enough to trigger
the Higgs boson invisible decay. In addition, the fourth Majorana neutrino can
be a subdominant but highly detectable dark matter component. We perform a
global analysis of the current LHC data on the Higgs production and decay in
this type of SM4. The results show that the mass of the lightest fourth
Majorana neutrino is confined in the range GeV. Within the allowed
parameter space, the predicted effective cross-section for spin-independent
DM-nucleus scattering is , which is close to the current Xenon100 upper limit and is
within the reach of the Xenon1T experiment in the near future. The predicted
spin-dependent cross sections can also reach .Comment: arXiv admin note: substantial text overlap with arXiv:1110.293
The Age-Redshift Relationship of Old Passive Galaxies
We use 32 age measurements of passively evolving galaxies as a function of
redshift to test and compare the standard model (CDM) with the Universe. We show that the latter fits the data with a reduced
for a Hubble constant km
. By comparison, the optimal flat CDM
model, with two free parameters (including and km ), fits the age-\emph{z} data with a reduced .
Based solely on their values, both models appear to account
for the data very well, though the optimized CDM parameters are only
marginally consistent with those of the concordance model ( and km ). Fitting the age-
data with the latter results in a reduced . However,
because of the different number of free parameters in these models, selection
tools, such as the Akaike, Kullback and Bayes Information Criteria, favour
over CDM with a likelihood of
versus . These results are suggestive, though not yet
compelling, given the current limited galaxy age- sample. We carry out Monte
Carlo simulations based on these current age measurements to estimate how large
the sample would have to be in order to rule out either model at a confidence level. We find that if the real cosmology is CDM, a
sample of galaxy ages would be sufficient to rule out
at this level of accuracy, while galaxy ages would be required to
rule out CDM if the real Universe were instead .Comment: 36 pages, 13 figures, 1 table; accepted for publication in The
Astronomical Journal. arXiv admin note: text overlap with arXiv:1405.238
Dual Skipping Networks
Inspired by the recent neuroscience studies on the left-right asymmetry of
the human brain in processing low and high spatial frequency information, this
paper introduces a dual skipping network which carries out coarse-to-fine
object categorization. Such a network has two branches to simultaneously deal
with both coarse and fine-grained classification tasks. Specifically, we
propose a layer-skipping mechanism that learns a gating network to predict
which layers to skip in the testing stage. This layer-skipping mechanism endows
the network with good flexibility and capability in practice. Evaluations are
conducted on several widely used coarse-to-fine object categorization
benchmarks, and promising results are achieved by our proposed network model.Comment: CVPR 2018 (poster); fix typ
Machine learning of quantum phase transitions
Machine learning algorithms provide a new perspective on the study of
physical phenomena. In this paper, we explore the nature of quantum phase
transitions using multi-color convolutional neural-network (CNN) in combination
with quantum Monte Carlo simulations. We propose a method that compresses
dimensional space-time configurations to a manageable size and then use them as
the input for a CNN. We test our approach on two models and show that both
continuous and discontinuous quantum phase transitions can be well detected and
characterized. Moreover we show that intermediate phases, which were not
trained, can also be identified using our approach.Comment: 6 pages, 5 figure
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