4,019 research outputs found
Real-Time Simulation of Large Open Quantum Spin Systems driven by Measurements
We consider a large quantum system with spins whose dynamics is
driven entirely by measurements of the total spin of spin pairs. This gives
rise to a dissipative coupling to the environment. When one averages over the
measurement results, the corresponding real-time path integral does not suffer
from a sign problem. Using an efficient cluster algorithm, we study the
real-time evolution of a 2-d Heisenberg antiferromagnet, which is driven to a
disordered phase, either by sporadic measurements or by continuous monitoring
described by Lindblad evolution.Comment: 5 pages, 7 figure
Supersymmetry and Charged Current Events at HERA
A light stop, with an R-parity-violating coupling , has been
suggested as an explanation of the excess in high- neutral current events
observed at the HERA collider. We show that in this scheme a corresponding
excess in charged current events --- such as that reported by the H1
Collaboration --- can appear naturally, without calling for the presence of
light sleptons or additional R-parity-violating couplings, if there exists a
chargino lighter than the stop. The predicted event shapes agree well with the
data. The relevant region of parameter space is identified, taking into account
constraints coming from precision electroweak measurements, atomic parity
violation and recent searches for first-generation leptoquarks at the Tevatron
collider.Comment: 18 pages, LaTeX, 4 embedded figure
GRACE/SUSY Automatic Generation of Tree Amplitudes in the Minimal Supersymmetric Standard Model
GRACE/SUSY is a program package for generating the tree-level amplitude and
evaluating the corresponding cross section of processes of the minimal
supersymmetric extension of the standard model (MSSM). The Higgs potential
adopted in the system, however, is assumed to have a more general form
indicated by the two-Higgs-doublet model. This system is an extension of GRACE
for the standard model(SM) of the electroweak and strong interactions. For a
given MSSM process the Feynman graphs and amplitudes at tree-level are
automatically created. The Monte-Carlo phase space integration by means of
BASES gives the total and differential cross sections. When combined with
SPRING, an event generator, the program package provides us with the simulation
of the SUSY particle productions.Comment: 39 page, 1 figur
Automatic one-loop calculation of MSSM processes with GRACE
We have developed the system for the automatic computation of cross-sections,
{\tt GRACE/SUSY}, including the one-loop calculations for processes of the
minimal supersymmetric extension of the the standard model. For an application,
we investigate the process .Comment: 4 pages, 1 figure, Talk presented by Jimbo, M. at ACAT-0
Automatic Computation of Cross Sections in HEP
For the study of reactions in High Energy Physics (HEP) automatic computation
systems have been developed and are widely used nowadays. GRACE is one of such
systems and it has achieved much success in analyzing experimental data. Since
we deal with the cross section whose value can be given by calculating hundreds
of Feynman diagrams, we manage the large scale calculation, so that effective
symbolic manipulation, the treat of singularity in the numerical integration
are required. The talk will describe the software design of GRACE system and
computational techniques in the GRACE.Comment: 6 pages, Latex, ICCP
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