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Fermi Observation of the transitional pulsar binary XSS J12270-4859
Because of the disappearance of its accretion disk since the time period
around 2012 November--December, XSS J12270-4859 has recently been identified
as, in addition to PSR J1023+0038, another transitional millisecond pulsar
binary. We have carried out detailed analysis of the Fermi Large Area Telescope
data for the binary. While both spectra before and after the disk-disappearance
transition are well described by an exponentially cut-off power law, typical
for pulsars' emission in the Fermi's 0.2-300 GeV, a factor of 2 flux decrease
related to the transition is detected. A weak orbital modulation is seen, but
only detectable in the after-transition data, same to that found at X-rays. In
the long-term light curve of the source before the transition, a factor of 3
flux variations are seen. Comparing to the properties of J1023+0038, we disucss
the implications from these results. We suggest that since the modulation is
aligned with that at X-rays in orbital phase, it possibly arises due to the
occultation of the gamma-ray emitting region by the companion. The origin of
the variations in the long-term light curve is not clear, because the source
field also contains unidentified radio or X-ray sources and their contamination
can not be excluded. Multi-wavelength observations of the source field will
help identify the origin of the variations by detecting any related flux
changes from the in-field sources.Comment: 12 pages, 5 figures, 2 tables, submitted to Ap
Radiative Decays of the Higgs Boson to a Pair of Fermions
We revisit the radiative decays of the Higgs boson to a fermion pair
where denotes a fermion in the Standard Model
(SM). We include the chirality-flipping diagrams via the Yukawa couplings at
the order , the chirality-conserving contributions
via the top-quark loops of the order , and the
electroweak loops at the order . The QED correction is
about and contributes to the running of fermion
masses at a similar level, which should be taken into account for future
precision Higgs physics. The chirality-conserving electroweak-loop processes
are interesting from the observational point of view. First, the branching
fraction of the radiative decay is about a half of
that of , and that of is more than
four orders of magnitude larger than that of , both of which
reach about . The branching fraction of is
of the order . All the leptonic radiative decays are potentially
observable at the LHC Run 2 or the HL-LHC. The kinematic distributions for the
photon energy or the fermion pair invariant mass provide non-ambiguous
discrimination for the underlying mechanisms of the Higgs radiative decay. We
also study the process and evaluate the observability at
the LHC. We find it comparable to the other related studies and better than the
channel in constraining the charm-Yukawa coupling.Comment: 23 pages, 6 figures, 6 tables; Minor corrections, references updated,
version published in JHE
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