3,253 research outputs found
Right-Handed Sneutrino as Cold Dark Matter
We consider supersymmetric models with right-handed neutrinos where neutrino
masses are purely Dirac-type. In this model, right-handed sneutrino can be the
lightest supersymmetric particle and can be a viable candidate of cold dark
matter of the universe. Right-handed sneutrinos are never thermalized in the
early universe because of weakness of Yukawa interaction, but are effectively
produced by decays of various superparticles. We show that the present mass
density of right-handed sneutrino can be consistent with the observed dark
matter density.Comment: 4 pages, 1 figur
Search for doubly charged Higgs bosons using the same-sign diboson mode at the LHC
Doubly charged Higgs bosons are predicted in many new physics models with an
extended Higgs sector that contains a Higgs triplet field. Current experimental
searches have been focusing mainly on the scenario in which the same-sign
dilepton decay modes are the dominant ones. We study the scenario where the
vacuum expectation value of the triplet field is sufficiently large so that the
associated charged Higgs bosons decay dominantly to a pair of weak gauge bosons
instead. A detailed simulation of the signal and the backgrounds is performed
for the CERN Large Hadron Collider at the collision energy of 8 TeV and 14 TeV.
We find that different cuts should be imposed for the events, depending on
whether the doubly charged Higgs boson mass is greater than about 200 GeV. In
the higher mass region, the forward jet tagging proves to be useful in
enhancing the signal significance. We show the discovery reach of the LHC
running at 8 and 14 TeV, with two benchmark triplet vacuum expectation values.
With an integrated luminosity of 10 fb at 8 TeV, the doubly charged
Higgs boson with a mass of GeV can be tested at level in
such a scenario.Comment: 18 pages, 10 figures; published in Physical Review
Higgs Properties and Fourth Generation Leptons
It is possible that there are additional vector-like generations where the
quarks have mass terms that do not originate from weak symmetry breaking, but
the leptons only get mass through weak symmetry breaking. We discuss the impact
that the new leptons have on Higgs boson decay branching ratios and on the
range of allowed Higgs masses in such a model (with a single new vector-like
generation). We find that if the fourth generation leptons are too heavy to be
produced in Higgs decay, then the new leptons reduce the branching ratio for h
-> gamma gamma to about 30% of its standard-model value. The dependence of this
branching ratio on the new charged lepton masses is weak. Furthermore the
expected Higgs production rate at the LHC is very near its standard-model value
if the new quarks are much heavier than the weak scale. If the new quarks have
masses near the cutoff for the theory then for cutoffs greater than 10^15 GeV,
the new lepton masses cannot be much heavier than about 100 GeV and the Higgs
mass must have a value around 175 GeV.Comment: 8 pages, 8 figures, published versio
Application of the Bichromophoric Exciton Chirality Method to the Stereochemical Elucidation of Acyclic Polyols
The recently developed technique of bichromophoric derivatization
extends the utility of the exciton chirality method.
Selective introduction of two types of exciton chromophores to
two different types of hydroxyl groups gives rise to highly
characteristic CD curves. Pairs of chromophores are evaluated for
two different applications: 1) an oligosaccharide linkage analysis,
and 2) elucidation of stereochemistry in acyclic polyhydroxyl compounds with two or more stereocenters. For the latter application,
selective introduction of the 9-anthroate chromophore (lemax = 253
nm) at prirnary hydroxyls, together with the p-methoxycinnamate
chromophore (,1,m" = 311 nm) introduced at secondary hydroxyls of
stereocenters, gives rise to highly characteristic CD spectra. Examination by this method of all diastereomeric n-tetrose and n-peritose diethyl dithioacetals indicates that the anthroate/methoxycinnamate bichromophoric approach is a promising method for assignment of stereochemistry in 1,2,3-triols, 1,2.3,4-tetrols,and other polyhydroxylated compounds
Two new intermediate polars with a soft X-ray component
Aims. We analyze the first X-ray observations with XMM-Newton of 1RXS J070407.9+262501 and 1RXS 180340.0+401214, in
order to characterize their broad-band temporal and spectral properties, also in the UV/optical domain, and to confirm them as intermediate polars.
Methods. For both objects, we performed a timing analysis of the X-ray and UV/optical light curves to detect the white dwarf spin pulsations and study their energy dependence. For 1RXS 180340.0+401214 we also analyzed optical spectroscopic data to determine the orbital period. X-ray spectra were analyzed in the 0.2–10.0 keV range to characterize the emission properties of both sources.
Results. We find that the X-ray light curves of both systems are energy dependent and are dominated, below 3–5 keV, by strong pulsations at the white dwarf rotational periods (480 s for 1RXS J070407.9+262501 and 1520.5 s for 1RXS 180340.0+401214). In 1RXS 180340.0+401214 we also detect an X-ray beat variability at 1697 s which, together with our new optical spectroscopy, favours an orbital period of 4.4 h that is longer than previously estimated. Both systems show complex spectra with a hard (temperature up to 40 keV) optically thin and a soft (kT ∼ 85–100 eV) optically thick components heavily absorbed by material partially covering the X-ray sources.
Conclusions. Our observations confirm the two systems as intermediate polars and also add them as new members of the growing group of “soft” systems which show the presence of a soft X-ray blackbody component. Differences in the temperatures of the blackbodies are qualitatively explained in terms of reprocessing over different sizes of the white dwarf spot. We suggest that systems showing cooler soft X-ray blackbody components also possess white dwarfs irradiated by cyclotron radiation
Suboptimal quantum-error-correcting procedure based on semidefinite programming
In this paper, we consider a simplified error-correcting problem: for a fixed
encoding process, to find a cascade connected quantum channel such that the
worst fidelity between the input and the output becomes maximum. With the use
of the one-to-one parametrization of quantum channels, a procedure finding a
suboptimal error-correcting channel based on a semidefinite programming is
proposed. The effectiveness of our method is verified by an example of the
bit-flip channel decoding.Comment: 6 pages, no figure, Some notations differ from those in the PRA
versio
Phenomenology in the Zee Model with the A_4 Symmetry
The Zee model generates neutrino masses at the one-loop level by adding
charged SU(2)_L-singlet and extra SU(2)_L-doublet scalars to the standard model
of particle physics. As the origin of the nontrivial structure of the lepton
flavor mixing, we introduce the softly broken A_4 symmetry to the Zee model.
This model is compatible with the tribimaximal mixing which agrees well with
neutrino oscillation measurements. Then, a sum rule m_1 e^{i alpha_12} + 2 m_2
+ 3 m_3 e^{i alpha_32} = 0 is obtained and it results in Delta m^2_31 < 0 and
m_3 > 1.8*10^{-2}eV. The effective mass |(M_nu)_{ee}| for the neutrinoless
double beta decay is predicted as | (M_\nu)_{ee} | > 1.7*10^{-2}eV. The
characteristic particles in this model are SU(2)_L-singlet charged Higgs bosons
s^+_alpha (alpha=xi,eta,zeta) which are made from a 3-representation of A_4.
Contributions of s^+_alpha to the lepton flavor violating decays of charged
leptons are almost forbidden by an approximately remaining Z_3 symmetry; only
BR(tau to ebar mu mu) can be sizable by the flavor changing neutral current
interaction with SU(2)_L-doublet scalars. Therefore, s^+_alpha can be easily
light enough to be discovered at the LHC with satisfying current constraints.
The flavor structures of BR(s^-_alpha to ell nu) are also discussed.Comment: 26 pages, 4 figures, version accepted by PR
Dynamical evolution of the mass function and radial profile of the Galactic globular cluster system
Evolution of the mass function (MF) and radial distribution (RD) of the
Galactic globular cluster (GC) system is calculated using an advanced and a
realistic Fokker-Planck (FP) model that considers dynamical friction,
disc/bulge shocks and eccentric cluster orbits. We perform hundreds of FP
calculations with different initial cluster conditions, and then search a
wide-parameter space for the best-fitting initial GC MF and RD that evolves
into the observed present-day Galactic GC MF and RD. By allowing both MF and RD
of the initial GC system to vary, which is attempted for the first time in the
present Letter, we find that our best-fitting models have a higher peak mass
for a lognormal initial MF and a higher cut-off mass for a power-law initial MF
than previous estimates, but our initial total masses in GCs, M_{T,i} =
1.5-1.8x10^8 Msun, are comparable to previous results. Significant findings
include that our best-fitting lognormal MF shifts downward by 0.35 dex during
the period of 13 Gyr, and that our power-law initial MF models well-fit the
observed MF and RD only when the initial MF is truncated at >~10^5 Msun. We
also find that our results are insensitive to the initial distribution of orbit
eccentricity and inclination, but are rather sensitive to the initial
concentration of the clusters and to how the initial tidal radius is defined.
If the clusters are assumed to be formed at the apocentre while filling the
tidal radius there, M_{T,i} can be as high as 6.9x10^8 Msun, which amounts to
~75 per cent of the current mass in the stellar halo.Comment: To appear in May 2008 issue of MNRAS, 386, L6
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