1,855 research outputs found
Technicolor contribution to lepton + photon + missing energy events at the Tevatron
Events with one lepton, one photon and missing energy are the subject of
recent searches at the Fermilab Tevatron. We compute possible contributions to
these type of events from the process p pbar --> photon l nu_l nu_tau
nubar_tau, where l=e,mu in the context of a Low Scale Technicolor Model. We
find that with somewhat tighter cuts than the ones used in the CDF search, it
could be possible to either confirm or exclude this model in a small region of
its parameter space.Comment: 4 pages, 3 figures. Improved text and figures, including comments and
new reference
Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC
Heavy sterile neutrinos with masses below can induce trilepton events
at the 14 TeV LHC through purely leptonic decays of and where the heavy neutrino will be
in an intermediate state on its mass shell. Discovery and exclusion limits for
the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate
Analysis (MVA) methods in this study. We also show that it is possible to
discriminate between a Dirac and a Majorana heavy neutrino, even when lepton
number conservation cannot be directly tested due to unobservability of the
final state neutrino. This discrimination is done by exploiting a combined set
of kinematic observables that differ between the Majorana vs. Dirac cases. We
find that the MVA method can greatly enhance the discovering and discrimination
limits in comparison with the CC method. For a 14-TeV collider with
integrated luminosity of 3000 , sterile neutrinos can be found
with 5 significance if heavy-to-light neutrino mixings , while the Majorana vs. Dirac type can be
distinguished if or even
if one of the mixing elements is at least an order
of magnitude smaller than the other.Comment: 10 pages, 12 figure
Search for Heavy Sterile Neutrinos in Trileptons at the LHC
We present a search strategy for both Dirac and Majorana sterile neutrinos
from the purely leptonic decays of and
at the 14 TeV LHC. The discovery and exclusion
limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and
Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and
Majorana sterile neutrinos by exploiting a set of kinematic observables which
differ between the Dirac and Majorana cases. We find that the MVA method,
compared to the more common CC method, can greatly enhance the discovery and
discrimination limits. Two benchmark points with sterile neutrino mass GeV and 50 GeV are tested. For an integrated luminosity of 3000 , sterile neutrinos can be found with significance if
heavy-to-light neutrino mixings ,
while Majorana vs. Dirac discrimination can be reached if at least one of the
mixings is of order .Comment: 4 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1703.0193
Probing the Majorana neutrinos and their CP violation in decays of charged scalar mesons
Some of the outstanding questions of particle physics today concern the
neutrino sector, in particular whether there are more neutrinos than those
already known and whether they are Dirac or Majorana particles.There are
different ways to explore these issues. In this article we describe
neutrino-mediated decays of charged pseudoscalar mesons such as ,
and , in scenarios where extra neutrinos are heavy and can
be on their mass shell. We discuss semileptonic and leptonic decays of such
kinds. We investigate possible ways of using these decays in order to
distinguish between the Dirac and Majorana character of neutrinos. Further, we
argue that there are significant possibilities of detecting CP violation in
such decays when there are at least two almost degenerate Majorana neutrinos
involved. This latter type of scenario fits well into the known neutrino
minimal standard model (MSM) which could simultaneously explain the Dark
Matter and Baryon Asymmetry of the Universe.Comment: v3: 37 pages, 14 figures; minor typographical errors corrected;
published in Symmetr
Long-term X-ray changes in the emission from the anomalous X-ray pulsar 4U 0142+61
We present results obtained from X-ray observations of the anomalous X-ray
pulsar (AXP) 4U 0142+61 taken between 2000-2007 using XMM-Newton, Chandra and
Swift. In observations taken before 2006, the pulse profile is observed to
become more sinusoidal and the pulsed fraction increased with time. These
results confirm those derived using the Rossi X-ray Timing Explorer and expand
the observed evolution to energies below 2 keV. The XMM-Newton total flux in
the 0.5-10 keV band is observed to be nearly constant in observations taken
before 2006, while an increase of ~10% is seen afterwards and coincides with
the burst activity detected from the source in 2006-2007. After these bursts,
the evolution towards more sinusoidal pulse profiles ceased while the pulsed
fraction showed a further increase. No evidence for large-scale, long-term
changes in the emission as a result of the bursts is seen. The data also
suggest a correlation between the flux and hardness of the spectrum, with
brighter observations on average having a harder spectrum. As pointed out by
other authors, we find that the standard blackbody plus power-law model does
not provide the best spectral fit to the emission from 4U 0142+61. We also
report on observations taken with the Gemini telescope after two bursts. These
observations show source magnitudes consistent with previous measurements. Our
results demonstrate the wide range of X-ray variability characteristics seen in
AXPs and we discuss them in light of current emission models for these sources.Comment: 10 pages, 9 figures, in emulateapj style. Submitted to Ap
Neutrino emission rates in highly magnetized neutron stars revisited
Magnetars are a subclass of neutron stars whose intense soft-gamma-ray bursts
and quiescent X-ray emission are believed to be powered by the decay of a
strong internal magnetic field. We reanalyze neutrino emission in such stars in
the plausibly relevant regime in which the Landau band spacing of both protons
and electrons is much larger than kT (where k is the Boltzmann constant and T
is the temperature), but still much smaller than the Fermi energies. Focusing
on the direct Urca process, we find that the emissivity oscillates as a
function of density or magnetic field, peaking when the Fermi level of the
protons or electrons lies about 3kT above the bottom of any of their Landau
bands. The oscillation amplitude is comparable to the average emissivity when
the Landau band spacing mentioned above is roughly the geometric mean of kT and
the Fermi energy (excluding mass), i. e., at fields much weaker than required
to confine all particles to the lowest Landau band. Since the density and
magnetic field strength vary continuously inside the neutron star, there will
be alternating surfaces of high and low emissivity. Globally, these
oscillations tend to average out, making it unclear whether there will be any
observable effects.Comment: 7 pages, 2 figures; accepted for publication in Astronomy &
Astrophysic
- …