21,121 research outputs found
Measurement of light mesons at RHIC by the PHENIX experiment
The PHENIX experiment at RHIC has measured a variety of light neutral mesons
(, K, , , , ) via
multi-particle decay channels over a wide range of transverse momentum. A
review of the recent results on the production rates of light mesons in p+p and
their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at
different energies is presented.Comment: 5 pages, 4 figures, talk given at Hard Probes 2008 conference in La
Toja, Spain. submitted to EPJ
Happiness Research and Cost-Benefit Analysis
A growing body of research on happiness or subjective well-being (SWB) shows, among other things, that people adapt to many injuries more rapidly than is commonly thought, fail to predict the degree of adaptation and hence overestimate the impact of those injuries on their SWB, and, similarly, enjoy small or moderate rather than significant changes in SWB in response to significant changes in income. Some researchers believe that these findings pose a challenge to cost-benefit analysis, and argue that project evaluation decision-procedures based on economic premises should be replaced with procedures that directly maximize subjective well-being. This view turns out to be wrong or, at best, premature. Cost-benefit analysis remains a viable decision-procedure. However, some of the findings in the happiness literature can be used to generate valuations for cost-benefit analysis where current approaches have proven inadequate.
High transverse momentum suppression and surface effects in Cu+Cu and Au+Au collisions within the PQM model
We study parton suppression effects in heavy-ion collisions within the Parton
Quenching Model (PQM). After a brief summary of the main features of the model,
we present comparisons of calculations for the nuclear modification and the
away-side suppression factor to data in Au+Au and Cu+Cu collisions at 200 GeV.
We discuss properties of light hadron probes and their sensitivity to the
medium density within the PQM Monte Carlo framework.Comment: Comments: 6 pages, 8 figures. To appear in the proceedings of Hot
Quarks 2006: Workshop for Young Scientists on the Physics of
Ultrarelativistic Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May
200
Multi-particle Correlations in Quaternionic Quantum Systems
We investigate the outcomes of measurements on correlated, few-body quantum
systems described by a quaternionic quantum mechanics that allows for regions
of quaternionic curvature. We find that a multi-particle interferometry
experiment using a correlated system of four nonrelativistic, spin-half
particles has the potential to detect the presence of quaternionic curvature.
Two-body systems, however, are shown to give predictions identical to those of
standard quantum mechanics when relative angles are used in the construction of
the operators corresponding to measurements of particle spin components.Comment: REVTeX 3.0, 16 pages, no figures, UM-P-94/54, RCHEP-94/1
Schwinger Algebra for Quaternionic Quantum Mechanics
It is shown that the measurement algebra of Schwinger, a characterization of
the properties of Pauli measurements of the first and second kinds, forming the
foundation of his formulation of quantum mechanics over the complex field, has
a quaternionic generalization. In this quaternionic measurement algebra some of
the notions of quaternionic quantum mechanics are clarified. The conditions
imposed on the form of the corresponding quantum field theory are studied, and
the quantum fields are constructed. It is shown that the resulting quantum
fields coincide with the fermion or boson annihilation-creation operators
obtained by Razon and Horwitz in the limit in which the number of particles in
physical states .Comment: 20 pages, Plain Te
Collapse models with non-white noises
We set up a general formalism for models of spontaneous wave function
collapse with dynamics represented by a stochastic differential equation driven
by general Gaussian noises, not necessarily white in time. In particular, we
show that the non-Schrodinger terms of the equation induce the collapse of the
wave function to one of the common eigenstates of the collapsing operators, and
that the collapse occurs with the correct quantum probabilities. We also
develop a perturbation expansion of the solution of the equation with respect
to the parameter which sets the strength of the collapse process; such an
approximation allows one to compute the leading order terms for the deviations
of the predictions of collapse models with respect to those of standard quantum
mechanics. This analysis shows that to leading order, the ``imaginary'' noise
trick can be used for non-white Gaussian noise.Comment: Latex, 20 pages;references added and minor revisions; published as J.
Phys. A: Math. Theor. {\bf 40} (2007) 15083-1509
Representations of U(1,q) and Constructive Quaternion Tensor Products
The representation theory of the group U(1,q) is discussed in detail because
of its possible application in a quaternion version of the Salam-Weinberg
theory.
As a consequence, from purely group theoretical arguments we demonstrate that
the eigenvalues must be right-eigenvalues and that the only consistent scalar
products are the complex ones. We also define an explicit quaternion tensor
product which leads to a set of additional group representations for integer
``spin''.Comment: 28 pages, Latex, Dipartimento di Fisica, Universita di Lecce
INFN-Sezione di Lecc
Test of Universality in the Ising Spin Glass Using High Temperature Graph Expansion
We calculate high-temperature graph expansions for the Ising spin glass model
with 4 symmetric random distribution functions for its nearest neighbor
interaction constants J_{ij}. Series for the Edwards-Anderson susceptibility
\chi_EA are obtained to order 13 in the expansion variable (J/(k_B T))^2 for
the general d-dimensional hyper-cubic lattice, where the parameter J determines
the width of the distributions. We explain in detail how the expansions are
calculated. The analysis, using the Dlog-Pad\'e approximation and the
techniques known as M1 and M2, leads to estimates for the critical threshold
(J/(k_B T_c))^2 and for the critical exponent \gamma in dimensions 4, 5, 7 and
8 for all the distribution functions. In each dimension the values for \gamma
agree, within their uncertainty margins, with a common value for the different
distributions, thus confirming universality.Comment: 13 figure
Phonon-modulated magnetic interactions and spin Tomonaga-Luttinger liquid in the p-orbital antiferromagnet CsO2
The magnetic response of antiferromagnetic CsO2, coming from the p-orbital
S=1/2 spins of anionic O2- molecules, is followed by 133Cs nuclear magnetic
resonance across the structural phase transition occuring at Ts1=61 K on
cooling. Above Ts1, where spins form a square magnetic lattice, we observe a
huge, nonmonotonic temperature dependence of the exchange coupling originating
from thermal librations of O2- molecules. Below Ts1, where antiferromagnetic
spin chains are formed as a result of p-orbital ordering, we observe a spin
Tomonaga-Luttinger-liquid behavior of spin dynamics. These two interesting
phenomena, which provide rare simple manifestations of the coupling between
spin, lattice and orbital degrees of freedom, establish CsO2 as a model system
for molecular solids.Comment: 9 pages, 5 figures (with Supplemental Material), to appear in
Physical Review Letter
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