3,974 research outputs found
Sterile neutrinos in neutrinoless double beta decay
We study possible contribution of the Majorana neutrino mass eigenstate
dominated by a sterile neutrino component to neutrinoless double beta
() decay. From the current experimental lower bound on the
-decay half-life of Ge we derive stringent constraints
on the mixing in a wide region of the values of mass. We
discuss cosmological and astrophysical status of in this mass region.Comment: 6 pages, 1 figure; v2 added comments and reference
Predictive Pati-Salam theory of fermion masses and mixing
We propose a Pati-Salam extension of the standard model incorporating a
flavor symmetry based on the group. The theory
realizes a realistic Froggatt-Nielsen picture of quark mixing and a predictive
pattern of neutrino oscillations. We find that, for normal neutrino mass
ordering, the atmospheric angle must lie in the higher octant, CP must be
violated in oscillations, and there is a lower bound for the
decay rate. For the case of inverted mass ordering, we find that the lower
atmospheric octant is preferred, and that CP can be conserved in oscillations.
Neutrino masses arise from a low-scale seesaw mechanism, whose messengers can
be produced by a portal at the LHC.Comment: 28 pages, 3 figures, published versio
Scalar meson mediated nuclear mu-e conversion
We study the nuclear mu-e conversion in the general framework of the
effective Lagrangian approach without referring to any specific realization of
the physics beyond the standard model (SM) responsible for lepton flavor
violation (LFV). We analyze the role of scalar meson exchange between the
lepton and nucleon currents and show its relevance for the coherent channel of
mu-e conversion. We show that this mechanism introduces modifications in the
predicted mu-e conversion rates in comparison with the conventional direct
nucleon mechanism, based on the contact type interactions of the nucleon
currents with the LFV leptonic current. We derive from the experimental data
lower limits on the mass scales of the generic LFV lepton-quark contact terms
and demonstrate that they are more stringent than the similar limits existing
in the literature.Comment: 14 pages, 1 figur
The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44
We present radio observations of a region in the vicinity of the young pulsar
PSR B1853+01 in the supernova remnant W44. The pulsar is located at the apex of
an extended feature with cometary morphology. We argue on the basis of its
morphology and its spectral index and polarization properties that this is a
synchrotron nebula produced by the spin down energy of the pulsar. The geometry
and physical parameters of this pulsar-powered nebula and W44 are used to
derive three different measures of the pulsar's transverse velocity. A range of
estimates between 315 and 470 km/s are derived, resulting in a typical value of
375 km/s. The observed synchrotron spectrum from radio to X-ray wavelengths is
used to put constraints on the energetics of the nebula and to derive the
parameters of the pulsar wind.Comment: ApJ Let (in press
Effective Lagrangian approach to nuclear mu-e conversion and the role of vector mesons
We study nuclear mu-e conversion in the general framework of an effective
Lagrangian approach without referring to any specific realization of the
physics beyond the standard model (SM) responsible for lepton flavor violation
(LFV). We examine the impact of a specific hadronization prescription on the
analysis of new physics in nuclear mu-e conversion and stress the importance of
vector meson exchange between lepton and nucleon currents. A new issue of this
mechanism is the presence of the strange quark vector current contribution
induced by the phi meson. This allows us to extract new limits on the LFV
lepton-quark effective couplings from the existing experimental data.Comment: 19 pages, 3 figures, to be published in Phys Rev
Interpretations of the NuTeV
We summarize theoretical explanations of the three discrepancy
between measured by NuTeV and predicted by the Standard Model
global fit. Possible new physics explanations ({\it e.g.} an unmized ) are
not compelling. The discrepancy would be reduced by a positive momentum
asymmetry in the strange sea; present experimental estimates of are
unreliable or incomplete. Upgrading the NuTeV analysis to NLO would alleviate
concerns that the discrepancy is a QCD effect.Comment: (proceedings for the NuFact'02 Workshop); reference and footnote
added, following the NuTeV proceeding
Neutrino predictions from a left-right symmetric flavored extension of the standard model
We propose a left-right symmetric electroweak extension of the Standard Model
based on the family symmetry. The masses of all
electrically charged Standard Model fermions lighter than the top quark are
induced by a Universal Seesaw mechanism mediated by exotic fermions. The top
quark is the only Standard Model fermion to get mass directly from a tree level
renormalizable Yukawa interaction, while neutrinos are unique in that they get
calculable radiative masses through a low-scale seesaw mechanism. The scheme
has generalized symmetry and leads to a restricted range of neutrino
oscillations parameters, with a nonzero neutrinoless double beta decay
amplitude lying at the upper ranges generically associated to normal and
inverted neutrino mass ordering.Comment: 20 pages, 4 figures. Published versio
DA495 - an aging pulsar wind nebula
We present a radio continuum study of the pulsar wind nebula (PWN) DA 495
(G65.7+1.2), including images of total intensity and linear polarization from
408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations
with the Effelsberg 100-m Radio Telescope. Removal of flux density
contributions from a superimposed \ion{H}{2} region and from compact
extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz,
with a spectral index below the break and
above it (). The
spectral break is more than three times lower in frequency than the lowest
break detected in any other PWN. The break in the spectrum is likely the result
of synchrotron cooling, and DA 495, at an age of 20,000 yr, may have
evolved from an object similar to the Vela X nebula, with a similarly energetic
pulsar. We find a magnetic field of 1.3 mG inside the nebula. After
correcting for the resulting high internal rotation measure, the magnetic field
structure is quite simple, resembling the inner part of a dipole field
projected onto the plane of the sky, although a toroidal component is likely
also present. The dipole field axis, which should be parallel to the spin axis
of the putative pulsar, lies at an angle of {\sim}50\degr east of the North
Celestial Pole and is pointing away from us towards the south-west. The upper
limit for the radio surface brightness of any shell-type supernova remnant
emission around DA 495 is OAWatt
m Hz sr (assuming a radio spectral index of ), lower than the faintest shell-type remnant known to date.Comment: 25 pages, accepted by Ap
A Low Frequency Survey of the Galactic Plane Near l=11 degrees: Discovery of Three New Supernova Remnants
We have imaged a 1 deg^2 field centered on the known Galactic supernova
remnant (SNR) G11.2-0.3 at 74, 330, and 1465 MHz with the Very Large Array
radio telescope (VLA) and 235 MHz with the Giant Metrewave Radio Telescope
(GMRT). The 235, 330, and 1465 MHz data have a resolution of 25 arcsec, while
the 74 MHz data have a resolution of 100 arcsec. The addition of this low
frequency data has allowed us to confirm the previously reported low frequency
turnover in the radio continuum spectra of the two known SNRs in the field:
G11.2-0.3 and G11.4-0.1 with unprecedented precision. Such low frequency
turnovers are believed to arise from free-free absorption in ionized thermal
gas along the lines of site to the SNRs. Our data suggest that the 74 MHz
optical depths of the absorbing gas is 0.56 and 1.1 for G11.2-0.3 and
G11.4-0.1, respectively. In addition to adding much needed low frequency
integrated flux measurements for two known SNRs, we have also detected three
new SNRs: G11.15-0.71, G11.03-0.05, and G11.18+0.11. These new SNRs have
integrated spectral indices between -0.44 and -0.80. Because of confusion with
thermal sources, the high resolution (compared to previous Galactic radio
frequency surveys) and surface brightness sensitivity of our observations have
been essential to the identification of these new SNRs. With this study we have
more than doubled the number of SNRs within just a 1 deg^2 field of view in the
inner Galactic plane. This result suggests that future low frequency
observations of the Galactic plane of similar quality may go a long way toward
alleviating the long recognized incompleteness of Galactic SNR catalogs.Comment: 31 pages, 9 figures. Figure 7 is in color. Accepted to A
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