4,015 research outputs found
Centrality dependence of hyperon global polarization in Au+Au collisions at RHIC
We present the centrality dependence of Lambda and Anti-Lambda hyperon global
polarization in Au+Au collisions at sqrt{s_NN}=62 GeV and 200 GeV measured with
the STAR detector at RHIC. Within the precision of the measurement, we observe
no centrality dependence of Lambda and Anti-Lambda hyperon global polarization
and within our acceptance it is consistent with zero. Different sources of
systematic uncertainties (feed down effects, spin precession) are discussed and
estimated. The obtained upper limit, |P_{Lambda,Anti-Lambda}| < 0.02, is
compared to theoretical predictions discussed recently in literatures.Comment: Talk given at QM 2006, The 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, November 14-20, 2006,
Shanghai, China; 4 pages, 2 figure
Measurements of Transverse Spin Effects with the Forward Pion Detector of STAR
Measurements by the STAR collaboration of neutral pion production at large
Feynman x (x_F) in the first polarized proton collisions at GeV
were reported previously. Cross sections measured at , 3.8 and 4.0
are found to be consistent with next-to-leading order perturbative QCD
calculations. The analyzing power is consistent with zero at negative x_F and
at positive x_F up to ~0.3, then grows more positive with increasing x_F. This
behavior can be described by phenomenological models including the Sivers
effect, the Collins effect or higher twist contributions in the initial and
final states. Forward calorimetry at STAR has been extended, and there are
plans for further expansion. An integrated luminosity of 6.8 pb^ with
average beam polarization of 60% from online polarimetry measurements was
sampled with the upgraded FPD in the 2006 RHIC run. This data sample will allow
for a detailed map of the \pi^0 analyzing power over kinematic variables
bounded by 0.3 < x_F < 0.6 and 1.2 < p_T < 5.0 GeV/c at GeV. The
expanded FPD has observed multi-photon final states expected to have "jet-like"
characteristics. The transverse spin dependence of jet-like events can
discriminate between the Collins and Sivers effects and lead to further
progress in understanding the origin of single spin asymmetries in forward
particle production. Data were also obtained at GeV for x_F ->
1 to test predictions based on phenomenological fits to earlier STAR results.
Recent results, the status of the analysis of 2006 run data and near-term plans
will be discussed.Comment: 4 pages, 3 figures, to be published in the proceedings of the 17th
International Spin Physics Symposium (SPIN2006), October 2-7, 2006, Kyoto,
Japa
One-Loop Pauli-Villars Regularization of Supergravity I: Canonical Gauge Kinetic Energy
It is shown that the one-loop coefficients of on-shell operators of standard
supergravity with canonical gauge kinetic energy can be regulated by the
introduction of Pauli-Villars chiral and abelian gauge multiplets, subject to a
condition on the matter representations of the gauge group. Aspects of the
anomaly structure of these theories under global nonlinear symmetries and an
anomalous gauge symmetry are discussed.Comment: 46 pages, full postscript also available from
http://phyweb.lbl.gov/theorygroup/papers/preprints.html/41981.ps . Misprints
and errors in equations present in the original version have been correcte
Learning from the history of disaster vulnerability and resilience research and practice for climate change
Humanity has long sought to explain and understand why environmental processes and phenomena contribute to and interfere with development processes, frequently through the terms and concepts of ‘vulnerability’ and ‘resilience’. Many proven ideas and approaches from development and disaster risk reduction literature are not fully considered by contemporary climate change work. This chapter describes the importance of older vulnerability and resilience research for contemporary investigations involving climate change, suggesting ways forward without disciplinary blinkers. Vulnerability and resilience as processes are explored alongside critiques of the post-disaster ‘return to normal’ paradigm. The importance of learning from already existing literature and experience is demonstrated for ensuring that complete vulnerability and resilience processes are accounted for by placing climate change within other contemporary development concerns
Gaugino Condensation with S-Duality and Field-Theoretical Threshold Corrections
We study gaugino condensation in the presence of an intermediate mass scale
in the hidden sector. S-duality is imposed as an approximate symmetry of the
effective supergravity theory. Furthermore, we include in the K\"ahler
potential the renormalization of the gauge coupling and the one-loop threshold
corrections at the intermediate scale. It is shown that confinement is indeed
achieved. Furthermore, a new running behaviour of the dilaton arises which we
attribute to S-duality. We also discuss the effects of the intermediate scale,
and possible phenomenological implications of this model.Comment: 19 pages, LaTeX, 3 postscript figures include
The 2D analogue of the Reissner-Nordstrom solution
A two-dimensional (2D) dilaton gravity model, whose static solutions have the
same features of the Reissner-Nordstrom solutions, is obtained from the
dimensional reduction of a four-dimensional (4D) string effective action
invariant under S-duality transformations. The black hole solutions of the 2D
model and their relationship with those of the 4D theory are discussed.Comment: 5 pages, Plain-Tex, no figure
One-loop Regularization of Supergravity II: The Dilaton and the Superfield Formulation
The on-shell regularization of the one-loop divergences of supergravity
theories is generalized to include a dilaton of the type occurring in effective
field theories derived from superstring theory, and the superfield structure of
the one-loop corrections is given. Field theory anomalies and quantum
contributions to soft supersymmetry breaking are discussed. The latter are
sensitive to the precise choice of couplings that generate Pauli-Villars
masses, which in turn reflect the details of the underlying theory above the
scale of the effective cut-off. With a view to the implementation the
Green-Schwarz and other mechanisms for canceling field theory anomalies under a
U(1) gauge transformation and under the T-duality group of modular
transformations, we show that the K\"ahler potential renormalization for the
untwisted sector of orbifold compactification can be made invariant under these
groups.Comment: 46 pages, full postscript also available from
http://phyweb.lbl.gov/theorygroup/papers/43259.p
Making Ends Meet: String Unification and Low-Energy Data
A long-standing problem in string phenomenology has been the fact that the
string unification scale disagrees with the GUT scale obtained by extrapolating
low-energy data within the framework of the minimal supersymmetric standard
model (MSSM). In this paper we examine several effects that may modify the
minimal string predictions and thereby bring string-scale unification into
agreement with low-energy data. These include heavy string threshold
corrections, non-standard hypercharge normalizations, light SUSY thresholds,
intermediate gauge structure, and thresholds arising from extra matter beyond
the MSSM. We explicitly evaluate these contributions within a variety of
realistic free-fermionic string models, including the flipped SU(5), SO(6) x
SO(4), and various SU(3) x SU(2) x U(1) models, and find that most of these
sources do not substantially alter the minimal string predictions. Indeed, we
find that the only way to reconcile string unification with low-energy data is
through certain types of extra matter. Remarkably, however, many of the
realistic string models contain precisely this required matter in their
low-energy spectra.Comment: 10 pages, standard LaTeX, 1 figure (Encapsulated PostScript), version
published in Phys. Rev. Lett. 75 (1995) 264
On the Interacting Chiral Gauge Field Theory in D=6 and the Off-Shell Equivalence of Dual Born-Infeld-Like Actions
A canonical action describing the interaction of chiral gauge fields in D=6
Minkowski space-time is constructed. In a particular partial gauge fixing it
reduces to the action found by Perry and Schwarz. The additional gauge
symmetries are used to show the off-shell equivalence of the dimensional
reduction to D=5 Minkowski space-time of the chiral gauge field canonical
action and the Born-Infeld canonical action describing an interacting D=5
Abelian vector field. Its extension to improve the on-shell equivalence
arguments of dual D-brane actions to off-shell ones is discussed.Comment: 18 page
Semileptonic Hyperon Decays and CKM Unitarity
Using a technique that is not subject to first-order SU(3) symmetry breaking
effects, we determine the element of the CKM matrix from data on
semileptonic hyperon decays. We obtain =0.2250(27). This value is of
similar precision to the one derived from , but higher and in better
agreement with the unitarity requirement, .Comment: 3 pages, 1 tabl
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