539 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
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
The quark fragmentation fractions at LHCb and meson decays with heavy quark spectators
We study the current estimates of to extract the
fragmentation fraction at the LHCb. A rather robust estimate of
based on factorization and lattice results for the form
factor gives with a error. We also revisit the
extraction of using instead of the theoretical cleaner
but more suppressed channel . We also find a tension on the
predictions of and considering the
measurements of these modes at LHCb, and find that, within a
uncertainty, only the lower end of the current prediction range would be consistent with the LHCb measurements.Comment: 11 pages, 2 figure
Triple Photon Production at the Tevatron in Technicolor Models
We study the process p bar{p} --> gamma gamma gamma as a signal for associated photon-technipion production at the Tevatron. This is a clean signature with relatively low background. Resonant and non-resonant contributions are included and we show that technicolor models can be effectively probed in this mode
CP violation with Majorana neutrinos in K meson decays
We study the possibility of having CP asymmetries in the decay Kaon(+/-) ->
pion(-/+) lepton(+/-) lepton(+/-) (lepton = muon or electron). This decay
violates Lepton Number by two units and occurs only if there are Majorana
particles that mediate the transition. Even though the absolute rate is highly
suppressed by current bounds, we search for Majorana neutrino scenarios where
the CP asymmetry arising from the lepton sector could be sizeable. This is
indeed the case if there are two or more Majorana neutrinos with similar masses
in the range around 10^2 MeV. In particular, the asymmetry is potentially near
unity if two neutrinos are nearly degenerate, in the sense that the mass
difference is similar to the decay rate. The full decay, however, may be
difficult to detect not only because of the suppression caused by the
heavy-to-light lepton mixing, but also because of the long lifetime of the
heavy neutrino, which would induce large space separation between the two
vertices where the charge leptons are produced. This particular problem should
be less serious in heavier meson decays, as they involve heavier neutrinos with
shorter lifetimes.Comment: 13 pages, 5 figure
3-dimensional Rules for Finite-Temperature Loops
We present simple diagrammatic rules to write down Euclidean n-point
functions at finite temperature directly in terms of 3-dimensional momentum
integrals, without ever performing a single Matsubara sum. The rules can be
understood as describing the interaction of the external particles with those
of the thermal bath.Comment: 12 pages, 4 figures, to appear in Physics Letters
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