544 research outputs found
Neutron Electric Dipole Moment at Fixed Topology
We describe the finite volume effects of CP-odd quantities, such as the
neutron electric dipole moment and the anapole moment in the -vacuum,
under different topological sectors. We evaluate the three-point Green's
functions for the electromagnetic current in a fixed non-trivial topological
sector in order to extract these CP-odd observables. We discuss the role of
zero modes in the CP-odd Green's function and show that, in the quenched
approximation, there is a power divergence in the quark mass for CP-odd
quantities at finite volume.Comment: 12 pages, revised manuscript to be publishe
Determination of the strange-quark mass from QCD pseudoscalar sum rules
A new determination of the strange-quark mass is discussed, based on the
two-point function involving the axial-vector current divergences. This Green
function is known in perturbative QCD up to order O(alpha_s^3), and up to
dimension-six in the non-perturbative domain. The hadronic spectral function is
parametrized in terms of the kaon pole, followed by its two radial excitations,
and normalized at threshold according to conventional chiral-symmetry. The
result of a Laplace transform QCD sum rule analysis of this two-point function
is: m_s(1 GeV^2) = 155 pm 25 MeV.Comment: Invited talk given by CAD at QCD98, Montpellier, July 1998. To appear
in Nucl.Phys.B Proc.Suppl. Latex File. Four (double column) page
Anomalies, Hawking Radiations and Regularity in Rotating Black Holes
This is an extended version of our previous letter hep-th/0602146. In this
paper we consider rotating black holes and show that the flux of Hawking
radiation can be determined by anomaly cancellation conditions and regularity
requirement at the horizon. By using a dimensional reduction technique, each
partial wave of quantum fields in a d=4 rotating black hole background can be
interpreted as a (1+1)-dimensional charged field with a charge proportional to
the azimuthal angular momentum m. From this and the analysis gr-qc/0502074,
hep-th/0602146 on Hawking radiation from charged black holes, we show that the
total flux of Hawking radiation from rotating black holes can be universally
determined in terms of the values of anomalies at the horizon by demanding
gauge invariance and general coordinate covariance at the quantum level. We
also clarify our choice of boundary conditions and show that our results are
consistent with the effective action approach where regularity at the future
horizon and vanishing of ingoing modes at r=\infty are imposed (i.e. Unruh
vacuum).Comment: 21 pages, minor corrections, added an appendix to summarize our
notations for the Kaluza-Klein reductio
Consistent analysis of the reaction and
The production of mesons in the reactions and
is described consistently within a relativistic meson exchange
model of hadronic interactions. The photoproduction can be described quite well
over the entire energy range of available data by considering an and a
resonance, in addition to the -channel mesonic current. The
observed angular distribution is due to the interference between the
-channel and the nucleon resonance - and -channel contributions. Our
analysis yields positions close to 1650 MeV and 1870 MeV for the and
resonances, respectively. We argue that, at present, identifying these
states with the known resonance and the missing
resonance predicted at 1880 MeV, respectively, would be premature. It is found
that the nucleonic current is relatively small and that the
coupling constant cannot be much larger than . As for the
reaction, different current contributions are
constrained by a combined analysis of this and the photoproduction reaction.
Difficulties to simultaneously account for the 47-MeV and 144-MeV angular
distributions measured by the COSY-11 and DISTO collaborations, respectively,
are addressed.Comment: minor revision, scheduled to a appear in Phys. Rev. C 69 (May 2004),
revtex, 17 pages, 10 figures, 3 table
Precise Determination of |V{us}| from Lattice Calculations of Pseudoscalar Decay Constants
Combining the ratio of experimental kaon and pion decay widths, Gamma(K to mu
antineutrino{mu} (gamma)) / Gamma(pi to mu \antineutrino (gamma)), with a
recent lattice gauge theory calculation of f{K}/f{pi} provides a precise value
for the CKM quark mixing matrix element |V{us}|=0.2236(30) or if 3 generation
unitarity is assumed |V{us}|=0.2238(30). Comparison with other determinations
of that fundamental parameter, implications, and an outlook for future
improvements are given
Lattice QCD calculation of scattering length
We study s-wave pion-pion () scattering length in lattice QCD for
pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered
fermion formulation, we calculate the four-point functions for isospin
I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order
to extrapolate our simulation results. Extrapolating to the physical pion mass
gives the scattering lengths as and for isospin I=2 and 0 channels, respectively. Our lattice
simulation for scattering length in the I=0 channel is an exploratory
study, where we include the disconnected contribution, and our preliminary
result is near to its experimental value. These simulations are performed with
MILC 2+1 flavor gauge configurations at lattice spacing fm.Comment: Remove some typo
Analytic Confinement and Regge Trajectories
A simple relativistic quantum field model with the Yukawa-type interaction is
considered to demonstrate that the analytic confinement of the constituent
("quarks") and carrier ("gluons") particles explains qualitatively the basic
dynamical properties of the spectrum of mesons considered as two-particle
stable bound states of quarks and gluons: the quarks and gluons are confined,
the glueballs represent bound states of massless gluons, the masses of mesons
are larger than the sum of the constituent quark masses and the Regge
trajectories of mesonic orbital excitations are almost linear.Comment: RevTeX, 16 pages, 3 figures and 2 table
Non-Commutative Geometry and Chiral Perturbation Lagrangian
Chiral perturbation lagrangian in the framework of non-commutative geometry
is considered in full detail. It is found that the explicit symmetry breaking
terms appear and some relations between the coupling constants of the theory
come out naturally. The WZW term also turns up on the same footing as the other
terms of the chiral lagrangian.Comment: Latex, 9 page
Meson Correlation Functions in the epsilon-Regime
We present a numerical pilot study of the meson correlation functions in the
epsilon-regime of chiral perturbation theory. Based on simulations with overlap
fermions we measured the axial and pseudo-scalar correlation functions, and we
discuss the implications for the leading low energy constants in the chiral
Lagrangian.Comment: 3 pages, 3 figures, talk presented at Lattice2003(chiral
Ground state of graphite ribbons with zigzag edges
We study the interaction effects on the ground state of nanographite ribbons
with zigzag edges. Within the mean-field approximation, we found that there are
two possible phases: the superconducting (SC) phase and the excitonic insulator
(EI). The two phases are separated by a first-order transition point. After
taking into account the low-lying fluctuations around the mean-field solutions,
the SC phase becomes a spin liquid phase with one gapless charge mode.
On the other hand, all excitations in the EI phase, especially the spin
excitations, are gapped.Comment: 6 pages, 3 figure
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