16,033 research outputs found
Constraining the Higgs sector from False Vacua in the Next-to-Minimal Supersymmetric Standard Model
We study the mass, the mixing and the coupling with boson of the lightest
Higgs boson in the next-to-minimal supersymmetric standard model. The vacuum
structure of the Higgs potential is analyzed and the new false vacua are
discussed. The significant parameter region can be excluded by requiring that
the realistic vacuum is deeper than false vacua, which result in constraints on
the properties of the lightest Higgs boson.Comment: 23 pages, 8 figure
A look inside charmed-strange baryons from lattice QCD
The electromagnetic form factors of the spin-3/2 baryons, namely
, , and , are
calculated in full QCD on PACS-CS lattices with a pion mass of
156(9) MeV. The electric charge radii and magnetic moments from the and
multipole form factors are extracted. Results for the electric quadrupole
form factors, , are also given. Quark sector contributions are computed
individually for each observable and then combined to obtain the baryon
properties. We find that the charm quark contributions are systematically
smaller than the strange-quark contributions in the case of the charge radii
and magnetic moments. moments of the and
provide a statistically significant data to conclude that their electric charge
distributions are deformed to an oblate shape. Properties of the spin-1/2
and baryons are also computed and a thorough
comparison is given. This complete study gives valuable hints about the
heavy-quark dynamics in charmed hadrons.Comment: 14 pages, 14 figures. Includes a subsection on the systematic effect
Electromagnetic structure of charmed baryons in Lattice QCD
As a continuation of our recent work on the electromagnetic properties of the
doubly charmed baryon, we compute the charge radii and the magnetic
moments of the singly charmed , and the doubly charmed
baryons in 2+1 flavor Lattice QCD. In general, the charmed
baryons are found to be compact as compared to the proton. The charm quark acts
to decrease the size of the baryons to smaller values. We discuss the mechanism
behind the dependence of the charge radii on the light valence- and sea-quark
masses. The magnetic moments are found to be almost stable with respect to
changing quark mass. We investigate the individual quark sector contributions
to the charge radii and the magnetic moments. The magnetic moments of the
singly charmed baryons are found to be dominantly determined by the light quark
and the role of the charm quark is significantly enhanced for the doubly
charmed baryons.Comment: Updated results, improved analysis. Version to appear in JHE
How to Measure the Quantum State of Collective Atomic Spin Excitation
The spin state of an atomic ensemble can be viewed as two bosonic modes,
i.e., a quantum signal mode and a -numbered ``local oscillator'' mode when
large numbers of spin-1/2 atoms are spin-polarized along a certain axis and
collectively manipulated within the vicinity of the axis. We present a concrete
procedure which determines the spin-excitation-number distribution, i.e., the
diagonal elements of the density matrix in the Dicke basis for the collective
spin state. By seeing the collective spin state as a statistical mixture of the
inherently-entangled Dicke states, the physical picture of its multi-particle
entanglement is made clear.Comment: 6 pages, to appear in Phys. Rev.
Electromagnetic properties of doubly charmed baryons in Lattice QCD
We compute the electromagnetic properties of \Xi_cc baryons in 2+1 flavor
Lattice QCD. By measuring the electric charge and magnetic form factors of
\Xi_cc baryons, we extract the magnetic moments, charge and magnetic radii as
well as the \Xi_cc \Xi_cc \rho coupling constant, which provide important
information to understand the size, shape and couplings of the doubly charmed
baryons. We find that the two heavy charm quarks drive the charge radii and the
magnetic moment of \Xi_cc to smaller values as compared to those of, e.g., the
proton.Comment: 15 pages, 5 figures; added discussions and references, version
accepted by PL
Vector and axial-vector couplings of D and D* mesons in 2+1 flavor Lattice QCD
Using the axial-vector coupling and the electromagnetic form factors of the D
and D* mesons in 2+1 flavor Lattice QCD, we compute the D*D\pi, DD\rho and
D*D*\rho coupling constants, which play an important role in describing the
charm hadron interactions in terms of meson-exchange models. We also extract
the charge radii of D and D* mesons and determine the contributions of the
light and charm quarks separately.Comment: 19 pages, 3 figures; added references and comments, published versio
Numerical Study on GRB-Jet Formation in Collapsars
Two-dimensional magnetohydrodynamic simulations are performed using the
ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB
jet, taking account of realistic equation of state, neutrino cooling and
heating processes, magnetic fields, and gravitational force from the central
black hole and self gravity. It is found that neutrino heating processes are
not so efficient to launch a jet in this study. It is also found that a jet is
launched mainly by B_\phi fields that are amplified by the winding-up effect.
However, since the ratio of total energy relative to the rest mass energy in
the jet is not so high as several hundred, we conclude that the jets seen in
this study are not be a GRB jet. This result suggests that general relativistic
effects, which are not included in this study, will be important to generate a
GRB jet. Also, the accretion disk with magnetic fields may still play an
important role to launch a GRB jet, although a simulation for much longer
physical time (\sim 10-100 s) is required to confirm this effect. It is shown
that considerable amount of 56Ni is synthesized in the accretion disk. Thus
there will be a possibility for the accretion disk to supply sufficient amount
of 56Ni required to explain the luminosity of a hypernova. Also, it is shown
that neutron-rich matter due to electron captures with high entropy per baryon
is ejected along the polar axis. Moreover, it is found that the electron
fraction becomes larger than 0.5 around the polar axis near the black hole by
\nu_e capture at the region. Thus there will be a possibility that r-process
and r/p-process nucleosynthesis occur at these regions. Finally, much neutrons
will be ejected from the jet, which suggests that signals from the neutron
decays may be observed as the delayed bump of afterglow or gamma-rays.Comment: 54 pages with 19 postscript figures. Accepted for publication in ApJ.
High resolution version is available at
http://www2.yukawa.kyoto-u.ac.jp/~nagataki/collapsar.pd
Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7
Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which
is a type-I multiferroic compound with the largest magnetic-order induced
ferroelectric polarization ({\Delta}P=17mC/m2) reported, so far. We observed
two optical magnon branches: a solely electric dipole allowed one and a mixed
magnetoelectric resonance. The entangled magnetization and polarization
dynamics of the magnetoelectric resonance gives rise to unidirectional light
absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one
propagation direction but not for the opposite direction. Our systematic study
of the magnetic field and temperature dependence of magnon modes provides
information about the energies and symmetries of spin excitations, which is
required to develop a microscopic spin model of CaBaCo4O7.Comment: 5 pages, 4 figure
Spectra of Quarkonia at Finite Temperature
Finite-temperature spectra of heavy quarkonia are calculated by combining
potential model and thermofield dynamics formalisms. The mass spectra of the
heavy quarkonia with various quark contents are calculated. It is found that
binding mass of the quarkonium decreases as temperature increases.Comment: 12 pages, 1 figure. To appear Mod.Phys.Lett.
- …