27,453 research outputs found
A testable scenario of WIMPZILLA with Dark Radiation
As the electromagnetic gauge symmetry makes the electron stable, a new
abelian gauge symmetry may be responsible for the stability of superheavy dark
matter. The gauge boson associated with the new gauge symmetry naturally plays
the role of dark radiation and contributes to the effective number of `neutrino
species', which has been recently measured by Planck. We estimate the
contribution of dark radiation from the radiative decay of a scalar particle
induced by the WIMPZILLA in the loop. The scalar particle may affect the
invisible decay of the Higgs boson by the Higgs portal type coupling.Comment: 4 pages, 3 figure
Mass and angular momentum of black holes in 3D gravity theories with first order formalism
We apply the Wald formalism to obtain masses and angular momenta of black
holes in three dimensional gravity theories using the first order formalism.
Wald formalism suggests that the entropy of a black hole can be defined by an
integration of a conserved charge on the bifurcation horizon, and mass and
angular momentum of a black hole as an integration of some charge variation
form at spatial infinity. The action of three dimensional gravity theories can
be represented by a form including some auxiliary fields. As well-known
examples we have calculated masses and angular momenta of some black holes in
topologically massive gravity and new massive gravity theories using the first
order formalism. We have also calculated mass and angular momentum of BTZ black
hole and new type black hole in minimal massive gravity theory with the action
represented by the first order formalism. We have also calculated the entropy
and central charges of new type black hole. According to
correspondence we suggest that the left and right moving temperatures should be
equal to the Hawking temperature in the case of new type black hole in minimal
massive gravity.Comment: 35 pages, title changed back to original one, some contents are added
and correcte
Bounds on dark matter interpretation of Fermi-LAT GeV excess
Annihilation of light dark matter of GeV into
the Standard Model fermions has been suggested as a possible origin of the
gamma-ray excess at GeV energies in the Fermi-LAT data. In this paper, we
examine possible model-independent signatures of such dark matter models in
other experiments such as AMS-02, colliders, and cosmic microwave background
(CMB) measurements. We point out that first generation of fermion final states
is disfavored by the existing experimental data. Currently AMS-02 positron
measurements provide stringent bounds on cross sections of dark matter
annihilation into leptonic final states, and final state is in severe
tension with this constraint, if not ruled out. The channel will be
complementarily verified in an early stage of ILC and future CMB measurements.
Light quark final states () are relatively strongly constrained by the
LHC and dark matter direct detection experiments even though these bounds are
model-dependent. Dark matter signals from annihilations into
channels would be constrained by AMS-02 antiproton data which will be released
in very near future. In optimistic case, diffuse radio emission from nearby
galaxy (clusters) and the galactic center might provide another hint or limit
on dark matter annihilation.Comment: 20 pages, 3 figures; figures and text updated, discussion improved,
references added; updated to match published version in NP
An alternative interpretation for cosmic ray peaks
We propose an alternative mechanism based upon dark matter (DM)
interpretation for anomalous peak signatures in cosmic ray measurements,
assuming an extended dark sector with two DM species. This is contrasted with
previous effort to explain various line-like cosmic-ray excesses in the context
of DM models where the relevant DM candidate directly annihilates into Standard
Model (SM) particles. The heavier DM is assumed to annihilate to an on-shell
intermediate state. As the simplest choice, it decays directly into the lighter
DM along with an unstable particle which in turn decays to a pair of SM states
corresponding to the interesting cosmic anomaly. We show that a sharp continuum
energy peak can be readily generated under the proposed DM scenario, depending
on dark sector particle mass spectra. Remarkably, such a peak is robustly
identified as half the mass of the unstable particle. Furthermore, other
underlying mass parameters are analytically related to the shape of energy
spectrum. We apply this idea to the two well-known line excesses in the cosmic
photon spectrum: 130 GeV gamma-ray line and 3.5 keV X-ray line. Each observed
peak spectrum is well-reproduced by theoretical expectation predicated upon our
suggested mechanism, and moreover, our resulting best fits provide rather
improved chi-square values.Comment: 9 pages, 3 figure
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