14,055 research outputs found
Boosted Dark Matter in IceCube and at the Galactic Center
We show that the event excess observed by the IceCube collaboration at
TeV--PeV energies, usually interpreted as evidence for astrophysical neutrinos,
can be explained alternatively by the scattering of highly boosted dark matter
particles. Specifically, we consider a scenario where a PeV scalar
dark matter particle can decay to a much lighter dark fermion ,
which in turn scatters off nuclei in the IceCube detector. Besides these
events, which are exclusively shower-like, the model also predicts a secondary
population of events at originating from the
3-body decay , where is a pseudoscalar which
mediates dark matter--Standard Model interactions and whose decay products
include neutrinos. This secondary population also includes track-like events,
and both populations together provide an excellent fit to the IceCube data. We
then argue that a relic abundance of light Dark Matter particles , which
may constitute a subdominant component of the Dark Matter in the Universe, can
have exactly the right properties to explain the observed excess in GeV gamma
rays from the galactic center region. Our boosted Dark Matter scenario also
predicts fluxes of TeV positrons and photons from 3-body cascade decays of the heavy Dark Matter
particle , and we show how these can be used to constrain parts of the
viable parameter space of the model. Direct detection limits are weak due to
the pseudoscalar couplings of . Accelerator constraints on the
pseudoscalar mediator lead to the conclusion that the preferred mass of
is GeV and that large coupling to quarks but suppressed or
vanishing coupling to leptons are preferred.Comment: 26 pages, 9 figures, 2 tables. v2: References added, matches version
to be published in JHEP. v3: Acknowledgement adde
Analytical Solution for the SU(2) Hedgehog Skyrmion and Static Properties of Nucleons
An analytical solution for symmetric Skyrmion was proposed for the SU(2)
Skyrme model, which take the form of the hybrid form of a kink-like solution
and that given by the instanton method. The static properties of nucleons was
then computed within the framework of collective quantization of the Skyrme
model, with a good agreement with that given by the exact numeric solution. The
comparisons with the previous results as well as the experimental values are
also given.Comment: 4 pages, 2 figures, submited to Phys.Lett.
A Tale of Two Portals: Testing Light, Hidden New Physics at Future Colliders
We investigate the prospects for producing new, light, hidden states at a
future collider in a Higgsed dark model, which we call the
Double Dark Portal model. The simultaneous presence of both vector and scalar
portal couplings immediately modifies the Standard Model Higgsstrahlung
channel, , at leading order in each coupling. In addition, each
portal leads to complementary signals which can be probed at direct and
indirect detection dark matter experiments. After accounting for current
constraints from LEP and LHC, we demonstrate that a future Higgs
factory will have unique and leading sensitivity to the two portal couplings by
studying a host of new production, decay, and radiative return processes.
Besides the possibility of exotic Higgs decays, we highlight the importance of
direct dark vector and dark scalar production at machines, whose
invisible decays can be tagged from the recoil mass method.Comment: 47 pages, 9 figures, 1 table. v2: references added, version matched
to JHE
Memory-Efficient Topic Modeling
As one of the simplest probabilistic topic modeling techniques, latent
Dirichlet allocation (LDA) has found many important applications in text
mining, computer vision and computational biology. Recent training algorithms
for LDA can be interpreted within a unified message passing framework. However,
message passing requires storing previous messages with a large amount of
memory space, increasing linearly with the number of documents or the number of
topics. Therefore, the high memory usage is often a major problem for topic
modeling of massive corpora containing a large number of topics. To reduce the
space complexity, we propose a novel algorithm without storing previous
messages for training LDA: tiny belief propagation (TBP). The basic idea of TBP
relates the message passing algorithms with the non-negative matrix
factorization (NMF) algorithms, which absorb the message updating into the
message passing process, and thus avoid storing previous messages. Experimental
results on four large data sets confirm that TBP performs comparably well or
even better than current state-of-the-art training algorithms for LDA but with
a much less memory consumption. TBP can do topic modeling when massive corpora
cannot fit in the computer memory, for example, extracting thematic topics from
7 GB PUBMED corpora on a common desktop computer with 2GB memory.Comment: 20 pages, 7 figure
Seeking for sterile neutrinos with displaced leptons at the LHC
We study the signal of long-lived sterile neutrino at the LHC produced
through the decay of the boson. It decays into charged lepton and jets. The
characteristic signature is a hard prompt lepton and a lepton from the
displaced decay of the sterile neutrino, which leads to a bundle of displaced
tracks with large transverse impact parameter. Different from other studies, we
neither reconstruct the displaced vertex nor place requirement on its invariant
mass to maintain sensitivity for low sterile neutrino masses. Instead, we focus
on the displaced track from the lepton. A difficulty for low mass sterile
neutrino study is that the displaced lepton is usually \textit{non-isolated}.
Therefore, leptons from heavy flavor quark is the major source of background.
We closely follow a search for displaced electron plus muon search at CMS and
study their control regions, which is related to our signal regions, in great
detail to develop a robust estimation of the background for our signals. After
further optimization on the signal limiting the number of jets, low and
large lepton displacement to suppress SM background, we reach an
exclusion sensitivity of about () for the mixing angle
square at 10 (2) GeV sterile neutrino mass respectively. The strategy we
propose can cover the light sterile masses complimentary to beam dump and
forward detector experiments.Comment: 22 pages, 6 figures, 1 table; v2: matched to Journal version
A Light Higgs at the LHC and the B-Anomalies
After the Higgs discovery, the LHC has been looking for new resonances,
decaying into pairs of Standard Model (SM) particles. Recently, the CMS
experiment observed an excess in the di-photon channel, with a di-photon
invariant mass of about 96~GeV. This mass range is similar to the one of an
excess observed in the search for the associated production of Higgs bosons
with the neutral gauge boson at LEP, with the Higgs bosons decaying to
bottom quark pairs. On the other hand, the LHCb experiment observed a
discrepancy with respect to the SM expectations of the ratio of the decay of
-mesons to -mesons and a pair of leptons, . This observation provides a hint of the
violation of lepton-flavor universality in the charged lepton sector and may be
explained by the existence of a vector boson originating form a symmetry and heavy quarks that mix with the left-handed down quarks.
Since the coupling to heavy quarks could lead to sizable Higgs di-photon rates
in the gluon fusion channel, in this article we propose a common origin of
these anomalies identifying a Higgs associated with the breakdown of the
symmetry and at the same time responsible to the quark
mixing, with the one observed at the LHC. We also discuss the constraints on
the identification of the same Higgs with the one associated with the bottom
quark pair excess observed at LEP.Comment: 34 pages, 5 figures, 3 tables. v2: 1 figure added, motivation
clarified, version matched to JHE
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