63 research outputs found
Cold atoms in U(3) gauge potentials
We explore the effects of artificial gauge potentials on ultracold
atoms. We study background gauge fields with both non-constant and constant
Wilson loops around plaquettes, obtaining the energy spectra in each case. The
scenario of metal-insulator transition for irrational fluxes is also examined.
Finally, we discuss the effect of such a gauge potential on the
superfluid-insulator transition for bosonic ultracold atoms.Comment: minor typos corrected; journal versio
The Direct Detection of Boosted Dark Matter at High Energies and PeV events at IceCube
We study the possibility of detecting dark matter directly via a small but
energetic component that is allowed within present-day constraints. Drawing
closely upon the fact that neutral current neutrino nucleon interactions are
indistinguishable from DM-nucleon interactions at low energies, we extend this
feature to high energies for a small, non-thermal but highly energetic
population of DM particle , created via the decay of a significantly more
massive and long-lived non-thermal relic , which forms the bulk of DM. If
interacts with nucleons, its cross-section, like the neutrino-nucleus
coherent cross-section, can rise sharply with energy leading to deep inelastic
scattering, similar to neutral current neutrino-nucleon interactions at high
energies. Thus, its direct detection may be possible via cascades in very large
neutrino detectors. As a specific example, we apply this notion to the recently
reported three ultra-high energy PeV cascade events clustered around PeV
at IceCube (IC). We discuss the features which may help discriminate this
scenario from one in which only astrophysical neutrinos constitute the event
sample in detectors like IC.Comment: v1: 6 pages, 4 figures; v2: More references added, minor text changes
for clarification; v3: Title change, major revision, updated references; v4:
Corrected Fig. 1b, Version published in JCA
Reconciling neutrino flux from heavy dark matter decay and recent events at IceCube
The IceCube detector has recently reported the observation of 28 events at
previously unexplored energies. While the statistics of the observed events are
still low, these events hint at the existence of a neutrino flux over and above
the atmospheric neutrino background. We investigate the possibility that a
significant component of the additional neutrino flux originates due to the
decay of a very heavy dark matter (VHDM) particle via several possible channels
into standard model particles. We show that a combination of a power law
astrophysical neutrino spectrum and the neutrino flux from the decay of a DM
species of mass in the range TeV improves the fit to the observed
neutrino events than that obtained from a best-fit astrophysical flux alone.
Assuming the existence of an astrophysical background described by the IC
best-fit, we also show that, for the decay of even heavier DM particles
( PeV), the same observations impose significant
constraints on the decay lifetimes. Allowing the astrophysical flux
normalization to vary leads to modifications of these limits, however, there is
still a range of dark matter mass and lifetime that is excluded by the IC
results.Comment: v1: 8 pages, 2 figures, 2 tables. v2: Minimization over
three-parameters (DM mass, lifetime and astrophysical power-law flux
normalization); better statistical quantification of fit-goodness;
conclusions unchanged; 15 pg, 3 figs, 2 tables; version to appear in JHE
On the interpretation of IceCube cascade events in terms of the Glashow resonance
The IceCube experiment (IC) has recently observed 2 cascade events with
energies between 1 and 10 PeV. This energy combined with the fact that no
muon-track events are observed may be interpreted as a cosmogenic
interacting in IC via the Glashow resonance (GR)
(hadrons or ). We point out a unique, background-free signature
of the GR, a single isolated muon unaccompanied by any shower activity from the
interaction , and propose it as a
test of this interpretation. We calculate the event numbers and find that a
single such event is expected over about a three-year period in IC. We also
show that, if event rates remain at their current levels then, even with the
GR, standard cosmogenic fluxes cannot easily explain the observations.
Moreover, if muon-tracks remain conspicuous by their absence, then new physics
needs to be invoked. As example scenarios in conformity with the observations,
we calculate event rates for neutrino decay and Lorentz-invariance violation.Comment: 4 pages, 2 figure
Charm decay in slow-jet supernovae as the origin of the IceCube ultra-high energy neutrino events
We investigate whether the recent ultra-high energy (UHE) neutrino events
detected at the IceCube neutrino observatory could come from the decay of
charmed mesons produced within the mildly relativistic jets of supernova-like
astrophysical sources. We demonstrate that the excess of neutrinos
observed by IceCube in the energy range 30 TeV--2 PeV can be explained by a
diffuse flux of neutrinos produced in such slow-jet supernovae, using the
values of astrophysical and QCD parameters within the theoretical uncertainties
associated with neutrino production from charmed meson decay in astrophysical
sources. We discuss the theoretical uncertainties inherent in the evaluation of
charm production in high energy hadronic collisions, as well as the
astrophysical uncertainties associated with slow-jet supernova sources. The
proton flux within the source, and therefore also the produced neutrino flux,
is cut off at around a few PeV, when proton cooling processes become dominant
over proton acceleration. This directly explains the sudden drop in event rates
at energies above a few PeV. We incorporate the effect of energy dependence in
the spectrum-weighted charm production cross-section and show that this has a
very significant effect on the shape, magnitude and cut-off energies for the
neutrino flux.Comment: 5 pages, 3 figure
Update on decaying and annihilating heavy dark matter with the 6-year IceCube HESE data
In view of the IceCube's 6-year high-energy starting events (HESE) sample, we
revisit the possibility that the updated data may be better explained by a
combination of neutrino fluxes from dark matter decay and an isotropic
astrophysical power-law than purely by the latter. We find that the combined
two-component flux qualitatively improves the fit to the observed data over a
purely astrophysical one, and discuss how these updated fits compare against a
similar analysis done with the 4-year HESE data. We also update fits involving
dark matter decay via multiple channels, without any contribution from the
astrophysical flux. We find that a DM-only explanation is not excluded by
neutrino data alone. Finally, we also consider the possibility of a signal from
dark matter annihilations and perform analogous analyses to the case of decays,
commenting on its implications.Comment: 36 pages, 14 figure
Probing decaying heavy dark matter with the 4-year IceCube HESE data
After the first four years of data taking, the IceCube neutrino telescope has
observed 54 high-energy starting events (HESE) with deposited energies between
20 TeV and 2 PeV. The background from atmospheric muons and neutrinos is
expected to be of about 20 events, all below 100 TeV, thus pointing towards the
astrophysical origin of about 8 events per year in that data set. However,
their precise origin remains unknown. Here, we perform a detailed analysis of
this event sample (considering simultaneously the energy, hemisphere and
topology of the events) by assuming two contributions for the signal events: an
isotropic power-law flux and a flux from decaying heavy dark matter. We fit the
mass and lifetime of the dark matter and the normalization and spectral index
of an isotropic power-law flux, for various decay channels of dark matter. We
find that a significant contribution from dark matter decay is always slightly
favored, either to explain the excess below 100 TeV, as in the case of decays
to quarks or, as in the case of neutrino channels, to explain the three
multi-PeV events. Also, we consider the possibility to interpret all the data
by dark matter decays only, considering various combinations of two decay
channels. We show that the decaying dark matter scenario provides a better fit
to HESE data than the isotropic power-law flux.Comment: v1: 44 pages, 12 figures; v2: Published version, no change
Probing decaying heavy dark matter with the 4-year IceCube HESE data
After the first four years of data taking, the IceCube neutrino telescope has
observed 54 high-energy starting events (HESE) with deposited energies between
20 TeV and 2 PeV. The background from atmospheric muons and neutrinos is
expected to be of about 20 events, all below 100 TeV, thus pointing towards the
astrophysical origin of about 8 events per year in that data set. However,
their precise origin remains unknown. Here, we perform a detailed analysis of
this event sample (considering simultaneously the energy, hemisphere and
topology of the events) by assuming two contributions for the signal events: an
isotropic power-law flux and a flux from decaying heavy dark matter. We fit the
mass and lifetime of the dark matter and the normalization and spectral index
of an isotropic power-law flux, for various decay channels of dark matter. We
find that a significant contribution from dark matter decay is always slightly
favored, either to explain the excess below 100 TeV, as in the case of decays
to quarks or, as in the case of neutrino channels, to explain the three
multi-PeV events. Also, we consider the possibility to interpret all the data
by dark matter decays only, considering various combinations of two decay
channels. We show that the decaying dark matter scenario provides a better fit
to HESE data than the isotropic power-law flux.Comment: v1: 44 pages, 12 figures; v2: Published version, no change
Forward charm-production models and prompt neutrinos at IceCube
We investigate the prompt neutrino background at IceCube, as determined from
forward charm. We consider the role of intrinsic charm and of a recombination
model and show that the contribution of these mechanisms is at most a factor
two.Comment: 10 pages, 6 figures; v2: Improved discussion, figures; no changes in
results; version accepted for publication in JHE
Revisiting the implications of CPT and unitarity for baryogenesis and leptogenesis
In the context of GUT baryogenesis models, a well-known theorem asserts that
CPT conservation and the unitarity of S-matrix require that the lowest order
contribution that leads to the generation of a non-zero net CP-violation via
the decay of a heavy particle must be to \mathcal{O}({\alpha_\slashed{B}}^3),
where \alpha_\slashed{B} is a baryon number (B) violating coupling. We
revisit this theorem (which holds for lepton number (L) violation, and hence
for leptogenesis as well) and examine its implications for models where the
particle content allows the heavy particle to also decay via modes which
conserve B (or L) in addition to modes which do not. We systematically expand
the S-matrix order by order in B\slash L-violating couplings, and show, in such
cases, that the net CP-violation is non-zero even to
\mathcal{O}({\alpha_\slashed{B}}^2), without actually contradicting the
theorem. By replacing a B/L violating coupling (usually constrained to be
small) by a relatively unconstrained B/L conserving one, our result may allow
for sufficient CP violation in models where it may otherwise have been
difficult to generate the observed baryon asymmetry. As an explicit application
of this result, we construct a model in low-scale leptogenesis.Comment: v2: Text improved and clarified; discussion on Leptogenesis model
improved, new Baryogenesis example added; version to appear in Phys.Rev.D; 10
pages, 4 fig
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