2,924 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
Galactic center GeV gamma-ray excess from dark matter with gauged lepton numbers
The recently observed excess in gamma-ray signal near the Galactic center
suggests that dark matter particles may annihilate into charged fermions that
produce gamma-ray to be observed. In this paper, we consider a leptonic dark
matter, which annihilates into the standard model leptons, and
, by the interaction of the gauged lepton number and fits the observed excess. Interestingly, the
necessary annihilation cross section for the observed gamma-ray flux provides a
good fit to the value for the relic abundance of dark matter. We identify the
preferred parameter space of the model after taking the existing experimental
constraints from the precision measurements including the muon , tau
decay, neutrino trident production, dark matter direct detection, LHC, and LEP
experiments.Comment: 18 pages, 8 figures, references added, matches published versio
Model-Independent Production of a Top-Philic Resonance at the LHC
We investigate the collider phenomenology of a color-singlet vector
resonance, which couples to the heaviest quarks, the top quarks, but very
weakly to the rest of the fermions in the Standard Model. We find that the
dominant production of such a resonance does not appear at the tree level -- it
rather occurs at the one-loop level in association with an extra jet.
Signatures like t anti-t plus jets readily emerge as a result of the subsequent
decay of the resonance into a pair of top quarks. Without the additional jet,
the resonance can still be produced off-shell, which gives a sizeable
contribution at low masses. The lower top quark multiplicity of the loop
induced resonance production facilitates its reconstruction as compared to the
tree level production that gives rise to more exotic signatures involving three
or even four top quarks in the final state. For all these cases, we discuss the
constraints on the resonance production stemming from recent experimental
measurements in the top quark sector. We find that the top-philic vector
resonance remains largely unconstrained for the majority of the parameter
space, although this will be scrutinized closely in the Run 2 phase of the LHC.Comment: 32 pages, 16 figure
511 keV -ray emission from the galactic bulge by MeV millicharged dark matter
We propose a possible explanation for the recently observed anomalous 511 keV
line with a new "millicharged" fermion. This new fermion is light []. Nevertheless, it has never been observed by any collider
experiments by virtue of its tiny electromagnetic charge . In
particular, we constrain parameters of this millicharged particle if the 511
keV cosmic -ray emission from the galactic bulge is due to positron
production from this new particle.Comment: 3 pages, 1 figure, A talk given by J.C.Park at the 16th International
Conference on Supersymmetry and the Unification of Fundamental Interactions
(SUSY08), Seoul, Korea, June 16-21, 200
The effects of Thomson scattering and chemical mixing on early-time light curves of double peaked type IIb supernovae
Previous numerical simulations of double-peaked SNe IIb light curves have
demonstrated that the radius and mass of the hydrogen-rich envelope of the
progenitor star can significantly influence the brightness and timescale of the
early-time light curve around the first peak. In this study, we investigate how
Thomson scattering and chemical mixing in the SN ejecta affect the optical
light curves during the early stages of the SNe IIb using radiation
hydrodynamics simulations. By comparing the results from two different
numerical codes (i.e., \stella{} and \snec{}), we find that the optical
brightness of the first peak can be reduced by more than a factor of 3 due to
the effect of Thomson scattering that causes the thermalization depth to be
located below the Rosseland-mean photosphere, compared to the corresponding
case where this effect is ignored. We also observe a short-lived plateau-like
feature lasting for a few days in the early-time optical light curves of our
models, in contrast to typical observed SNe IIb that show a quasi-linear
decrease in optical magnitudes after the first peak. A significant degree of
chemical mixing between the hydrogen-rich envelope and the helium core in SN
ejecta is required to reconcile this discrepancy between the model prediction
and observation. Meanwhile, to properly reproduce the first peak, a significant
mixing of \nifs{} into the hydrogen-rich outermost layers should be restricted.
Our findings indicate that inferring the SN IIb progenitor structure from a
simplified approach that ignores these two factors may introduce substantial
uncertainty.Comment: 28 pages, 21 figures, accepted for Ap
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