23,598 research outputs found
Detecting Gluino-Containing Hadrons
When SUSY breaking produces only dimension-2 operators, gluino and photino
masses are of order 1 GeV or less. The gluon-gluino bound state has mass
1.3-2.2 GeV and lifetime > 10^{-5} - 10^{-10} s. This range of mass and
lifetime is largely unconstrained because missing energy and beam dump
techniques are ineffective. With only small modifications, upcoming K^0 decay
experiments can study most of the interesting range. The lightest
gluino-containing baryon (uds-gluino) is long-lived or stable; experiments to
find it and the uud-gluino are also discussed.Comment: 13 pp, 1 figure (uuencoded). Descendant of hep-ph/9504295,
hep-ph/9508291, and hep-ph/9508292, focused on experimental search
techniques. To be published in Phys Rev Let
Testing linear hypotheses in high-dimensional regressions
For a multivariate linear model, Wilk's likelihood ratio test (LRT)
constitutes one of the cornerstone tools. However, the computation of its
quantiles under the null or the alternative requires complex analytic
approximations and more importantly, these distributional approximations are
feasible only for moderate dimension of the dependent variable, say .
On the other hand, assuming that the data dimension as well as the number
of regression variables are fixed while the sample size grows, several
asymptotic approximations are proposed in the literature for Wilk's \bLa
including the widely used chi-square approximation. In this paper, we consider
necessary modifications to Wilk's test in a high-dimensional context,
specifically assuming a high data dimension and a large sample size .
Based on recent random matrix theory, the correction we propose to Wilk's test
is asymptotically Gaussian under the null and simulations demonstrate that the
corrected LRT has very satisfactory size and power, surely in the large and
large context, but also for moderately large data dimensions like or
. As a byproduct, we give a reason explaining why the standard chi-square
approximation fails for high-dimensional data. We also introduce a new
procedure for the classical multiple sample significance test in MANOVA which
is valid for high-dimensional data.Comment: Accepted 02/2012 for publication in "Statistics". 20 pages, 2 pages
and 2 table
Measurement of the mass of the Ï„ lepton
A data-driven energy scan in the immediate vicinity of the τ pair production threshold has been performed using the Beijing Spectrometer at the Beijing Electron-Positron Collider. Approximately 5 pb^(-1) of data, distributed over 12 scan points, have been collected. A previous mass value for the τ lepton, obtained using only the eμ final state, has been published. In this paper, the final BES result on the mass measurement is presented. The analysis is based on the combined data from the ee, eμ, eh, μμ, μh, and hh final states, where h denotes a charged π or K. A maximum likelihood fit to the τ pair production cross section data yields the value m_τ=1776.96_(-0.21)-0.17^(+0.18+0.25) MeV
The topological AC effect on noncommutative phase space
The Aharonov-Casher (AC) effect in non-commutative(NC) quantum mechanics is
studied. Instead of using the star product method, we use a generalization of
Bopp's shift method. After solving the Dirac equations both on noncommutative
space and noncommutative phase space by the new method, we obtain the
corrections to AC phase on NC space and NC phase space respectively.Comment: 8 pages, Latex fil
A possible hadronic excess in psi(2S) decay and rho-pi puzzle
We examine the so-called rho-pi puzzle of the psi(2S) decay by incorporating
two inputs: One is the relative phase between the one-photon and the gluon
decay amplitude, and the other is a possible anomaly in the inclusive
nonelectromagnetic decay rate of psi(2S). We propose the possibility that in
the psi(2S) decay a hadronic decay process of long distance origin is important
in addition to the short-distance decay process. The amplitude of this
additional process should nearly cancel the three-gluon amplitude in the
exclusive psi(2S)---> 1-0- and turn the sum dominantly real in contrast to the
J/psi decay. We present general consequences of this mechanism and then briefly
look into two models which possibly explain the course of this additional
amplitude.Comment: 14 pages, 2 Tables, and 3 eps figures. Replaces the original version
with a minor change in the title and inclusion of more references. The
version to appear in Phys. Rev.
Effect of the tensor force on the charge-exchange spin-dipole excitations of 208Pb
The charge-exchange spin-dipole (SD) excitations of 208Pb are studied by
using a fully self-consistent Skyrme Hartree-Fock plus Random Phase
Approximation (HF+RPA) formalism which includes the tensor interaction. It is
found, for the first time, that the tensor correlations have a unique,
multipole-dependent effect on the SD excitations, that is, they produce
softening of 1- states, but hardening of 0- and 2- states. This paves the way
to a clear assessment of the strength of the tensor terms. We compare our
results with a recent measurement, showing that our choice of tensor terms
improves the agreement with experiment. The robustness of our results is
supported by the analytic form of the tensor matrix elements.Comment: 4 pages, 1 figure, 2 table
Hadronic Contributions to the Photon Vacuum Polarization and their Role in Precision Physics
I review recent evaluations of the hadronic contribution to the shift in the
fine structure constant and to the anomalous magnetic moment of the muon.
Substantial progress in a precise determination of these important observables
is a consequence of substantially improved total cross section measurement by
the CMD-2 and BES II collaborations and an improved theoretical understanding.
Prospects for further possible progress is discussed.Comment: 17 pages 7 figures 2 tables, update: incl. CMD-2 data, reference
A Random Matrix Approach to VARMA Processes
We apply random matrix theory to derive spectral density of large sample
covariance matrices generated by multivariate VMA(q), VAR(q) and VARMA(q1,q2)
processes. In particular, we consider a limit where the number of random
variables N and the number of consecutive time measurements T are large but the
ratio N/T is fixed. In this regime the underlying random matrices are
asymptotically equivalent to Free Random Variables (FRV). We apply the FRV
calculus to calculate the eigenvalue density of the sample covariance for
several VARMA-type processes. We explicitly solve the VARMA(1,1) case and
demonstrate a perfect agreement between the analytical result and the spectra
obtained by Monte Carlo simulations. The proposed method is purely algebraic
and can be easily generalized to q1>1 and q2>1.Comment: 16 pages, 6 figures, submitted to New Journal of Physic
Computation and visualization of photonic quasicrystal spectra via Blochs theorem
Previous methods for determining photonic quasicrystal (PQC) spectra have
relied on the use of large supercells to compute the eigenfrequencies and/or
local density of states (LDOS). In this manuscript, we present a method by
which the energy spectrum and the eigenstates of a PQC can be obtained by
solving Maxwells equations in higher dimensions for any PQC defined by the
standard cut-and-project construction, to which a generalization of Blochs
theorem applies. In addition, we demonstrate how one can compute band
structures with defect states in the higher-dimensional superspace with no
additional computational cost. As a proof of concept, these general ideas are
demonstrated for the simple case of one-dimensional quasicrystals, which can
also be solved by simple transfer-matrix techniques.Comment: Published in Physical Review B, 77 104201, 200
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