34,091 research outputs found
Charm mixing in the Standard Model and beyond
The motivation most often cited in searches for D0-anti-D0 mixing and
CP-violation in charm system lies with the possibility of observing a signal
from New Physics which dominates that from the Standard Model. We review recent
theoretical predictions and experimental constraints on D0-anti-D0 mixing
parameters, concentrating on possible effects of New Physics.Comment: 8 pages, 2 figures, Invited talk at International Workshop on
Tau-Charm Physics (Charm 2006), Beijing, China, 5-7 Jun 200
B_s decays at Belle
We report recent results obtained with the Belle detector using a 23.6
fb^{-1} data sample collected on the Y(5S) resonance at the KEKB asymmetric
energy e^+ e^- collider. Inclusive semileptonic B_s^0 -> X^+ l^- \nu decays are
studied for the first time and the branching fraction is measured. Combining
the electron and muon channels, we obtain Bf(B_s^0 -> X^+ l^- \nu) = (10.2 \pm
0.8 \pm 0.9)%. Also, the radiative penguin decay B_s^0 -> \phi \gamma is
observed for the first time, and an improved upper limit for the decay B_s^0
\to \gamma \gamma is obtained.Comment: Proceedings of the EPS/HEP 2007 Conference, Manchester, England, July
2007 (on behalf of the Belle collaboration), 3 pages, 2 figure
Geometric Mean Neutrino Mass Relation
Present experimental data from neutrino oscillations have provided much
information about the neutrino mixing angles. Since neutrino oscillations only
determine the mass squared differences , the
absolute values for neutrino masses can not be determined using data just
from oscillations. In this work we study implications on neutrino masses from a
geometric mean mass relation which enables one to
determined the absolute masses of the neutrinos. We find that the central
values of the three neutrino masses and their errors to be , , and . Implications for cosmological observation, beta decay and
neutrinoless double beta decays are discussed.Comment: 7 pages. Talk given at COSPA06. A reference adde
Universal Scaling of the Neel Temperature of Near-Quantum-Critical Quasi-Two-Dimensional Heisenberg Antiferromagnets
We use a quantum Monte Carlo method to calculate the Neel temperature T_N of
weakly coupled S=1/2 Heisenberg antiferromagnetic layers consisting of coupled
ladders. This system can be tuned to different two-dimensional scaling regimes
for T > T_N. In a single-layer mean-field theory,
\chi_s^{2D}(T_N)=(z_2J')^{-1}, where \chi_s^{2D} is the exact staggered
susceptibility of an isolated layer, J' the inter-layer coupling, and z_2=2 the
layer coordination number. With a renormalized z_2, we find that this
relationship applies not only in the renormalized-classical regime, as shown
previously, but also in the quantum-critical regime and part of the
quantum-disordered regime. The renormalization is nearly constant; k_2 ~
0.65-0.70. We also study other universal scaling functions.Comment: 4 pages, 4 figure
Summary of Experimental Meson Physics
A summary of the present experimental status of meson physics is presented.
The presentation includes the new results presented at the MESON06 workshop, as
well as other recent experimental developments in the field.Comment: 15 pages, 6 figures, presented at 9th International Workshop on Meson
Production, Properties and Interaction, Krakow, Poland, June 200
Invisible Z decay width bounds on active-sterile neutrino mixing in the (3+1) and (3+2) models
In this work we consider the standard model extended with singlet sterile
neutrinos with mass in the eV range and mixed with the active neutrinos. The
active-sterile neutrino mixing renders new contributions to the invisible Z
decay width which, in the case of light sterile neutrinos, depends on the
active-sterile mixing matrix elements only. We then use the current
experimental value of the invisible Z decay width to obtain bounds on these
mixing matrix elements for both (3+1) and (3+2) models.Comment: 10 pages, 5 figure
Magnetic Excitations in the High Tc Iron Pnictides
We calculate the expected finite frequency neutron scattering intensity based
on the two-sublattice collinear antiferromagnet found by recent neutron
scattering experiments as well as by theoretical analysis on the iron
oxypnictide LaOFeAs. We consider two types of superexchange couplings between
Fe atoms: nearest-neighbor coupling J1 and next-nearest-neighbor coupling J2.
We show how to distinguish experimentally between ferromagnetic and
antiferromagnetic J1. Whereas magnetic excitations in the cuprates display a
so-called resonance peak at (pi,pi) (corresponding to a saddlepoint in the
magnetic spectrum) which is at a wavevector that is at least close to nesting
Fermi-surface-like structures, no such corresponding excitations exist in the
iron pnictides. Rather, we find saddlepoints near (pi,pi/2) and (0,pi/2)(and
symmetry related points). Unlike in the cuprates, none of these vectors are
close to nesting the Fermi surfaces.Comment: 4 pages, 5 figure
Theoretical overview on tau physics
Precise measurements of the tau lepton properties provide stringent tests of
the Standard Model structure and accurate determinations of its parameters. We
overview the present status of a few selected topics: lepton universality, QCD
tests and the determination of alpha_s, m_s and V_us from hadronic tau decays,
and lepton flavor violation phenomena.Comment: Invited talk at the International Workshop on Tau-Charm Physics
(Charm2006), Beijing, China, June 5-7, 2006. 8 pages, 2 figure
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