323 research outputs found
Unitarized Diffractive Scattering in QCD and Application to Virtual Photon Total Cross Sections
The problem of restoring Froissart bound to the BFKL-Pomeron is studied in an
extended leading-log approximation of QCD. We consider parton-parton scattering
amplitude and show that the sum of all Feynman-diagram contributions can be
written in an eikonal form. In this form dynamics is determined by the phase
shift, and subleading-logs of all orders needed to restore the Froissart bound
are automatically provided. The main technical difficulty is to find a way to
extract these subleading contributions without having to compute each Feynman
diagram beyond the leading order. We solve that problem by using nonabelian cut
diagrams introduced elsewhere. They can be considered as colour filters used to
isolate the multi-Reggeon contributions that supply these subleading-log terms.
Illustration of the formalism is given for amplitudes and phase shifts up to
three loops. For diffractive scattering, only phase shifts governed by one and
two Reggeon exchanges are needed. They can be computed from the
leading-log-Reggeon and the BFKL-Pomeron amplitudes. In applications, we argue
that the dependence of the energy-growth exponent on virtuality for
total cross section observed at HERA can be interpreted as the
first sign of a slowdown of energy growth towards satisfying the Froissart
bound. An attempt to understand these exponents with the present formalism is
discussed.Comment: 41 pages in revtex preprint format, with 10 figure
Raman study of carrier-overdoping effects on the gap in high-Tc superconducting cuprates
Raman scattering in the heavily overdoped (Y,Ca)Ba_2Cu_3O_{7-d} (T_c = 65 K)
and Bi_2Sr_2CaCu_2O_{8+d} (T_c = 55 K) crystals has been investigated. For the
both crystals, the electronic pair-breaking peaks in the A_{1g} and B_{1g}
polarizations were largely shifted to the low energies close to a half of
2Delta_0, Delta_0 being the maximum gap. It strongly suggests s-wave mixing
into the d-wave superconducting order parameter and the consequent
manifestation of the Coulomb screening effect in the B_{1g}-channel. Gradual
mixing of s-wave component with overdoping is not due to the change of crystal
structure symmetry but a generic feature in all high-T_c superconducting
cuprates.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B, Rapid
communicaito
Time-Dependent Partition-Free Approach in Resonant Tunneling Systems
An extended Keldysh formalism, well suited to properly take into account the
initial correlations, is used in order to deal with the time-dependent current
response of a resonant tunneling system. We use a \textit{partition-free}
approach by Cini in which the whole system is in equilibrium before an external
bias is switched on. No fictitious partitions are used. Besides the
steady-state responses one can also calculate physical dynamical responses. In
the noninteracting case we clarify under what circumstances a steady-state
current develops and compare our result with the one obtained in the
partitioned scheme. We prove a Theorem of asymptotic Equivalence between the
two schemes for arbitrary time-dependent disturbances. We also show that the
steady-state current is independent of the history of the external perturbation
(Memory Loss Theorem). In the so called wide-band limit an analytic result for
the time-dependent current is obtained. In the interacting case we propose an
exact non-equilibrium Green function approach based on Time Dependent Density
Functional Theory. The equations are no more difficult than an ordinary Mean
Field treatment. We show how the scattering-state scheme by Lang follows from
our formulation. An exact formula for the steady-state current of an arbitrary
interacting resonant tunneling system is obtained. As an example the
time-dependent current response is calculated in the Random Phase
Approximation.Comment: final version, 18 pages, 9 figure
Solid-state laser system for laser cooling of Sodium
We demonstrate a frequency-stabilized, all-solid laser source at 589 nm with
up to 800 mW output power. The laser relies on sum-frequency generation from
two laser sources at 1064 nm and 1319 nm through a PPKTP crystal in a
doubly-resonant cavity. We obtain conversion efficiency as high as 2 W/W^2
after optimization of the cavity parameters. The output wavelength is tunable
over 60 GHz, which is sufficient to lock on the Sodium D2 line. The robustness,
beam quality, spectral narrowness and tunability of our source make it an
alternative to dye lasers for atomic physics experiments with Sodium atoms
Theoretical uncertainties in sparticle mass predictions from computational tools
We estimate the current theoretical uncertainty in sparticle mass predictions
by comparing several state-of-the-art computations within the minimal
supersymmetric standard model (MSSM). We find that the theoretical uncertainty
is comparable to the expected statistical errors from the Large Hadron Collider
(LHC), and significantly larger than those expected from a future e+e- Linear
Collider (LC). We quantify the theoretical uncertainty on relevant sparticle
observables for both LHC and LC, and show that the value of the error is
significantly dependent upon the supersymmetry (SUSY) breaking parameters. We
also present the theoretical uncertainty induced in fundamental-scale SUSY
breaking parameters when they are fitted from LHC measurements. Two regions of
the SUSY parameter space where accurate predictions are particularly difficult
are examined in detail: the large tan(beta) and focus point regimes.Comment: 22 pages, 6 figures; comment added pointing out that 2-loop QCD
corrections to mt are incorrect in some of the programs investigated. We give
the correct formul
The Fayet-Iliopoulos D-term and its renormalisation in softly-broken supersymmetric theories
We consider the renormalisation of the Fayet-Iliopoulos D-term in a
softly-broken abelian supersymmetric theory, and calculate the associated
beta-function through three loops. We show that there exists (at least through
three loops) a renormalisation group invariant trajectory for the coefficient
of the D-term, corresponding to the conformal anomaly solution for the soft
masses and couplings.Comment: 30 pages, Revtex, 15 Figures. Minor changes, and inadvertent omission
of author from this abstract correcte
Multipartite entangled states in coupled quantum dots and cavity-QED
We investigate the generation of multipartite entangled state in a system of
N quantum dots embedded in a microcavity and examine the emergence of genuine
multipartite entanglement by three different characterizations of entanglement.
At certain times of dynamical evolution one can generate multipartite entangled
coherent exciton states or multiqubit states by initially preparing the
cavity field in a superposition of coherent states or the Fock state with one
photon, respectively. Finally we study environmental effects on multipartite
entanglement generation and find that the decay rate for the entanglement is
proportional to the number of excitons.Comment: 9 pages, 4 figures, to appear in Phys. Rev.
Discovery and Development of Cyclic Peptide Inhibitors of CIB1
Calcium and integrin binding protein 1 (CIB1) is a small, intracellular protein recently implicated in survival and proliferation of triple-negative breast cancer (TNBC). Considering its interactions with PAK1 and downstream signaling, CIB1 has been suggested as a potential therapeutic target in TNBC. As such, CIB1 has been the focus of inhibitor discovery efforts. To overcome issues of potency and stability in previously reported CIB1 inhibitors, we deploy mRNA display to discover new cyclic peptide inhibitors with improved biophysical properties and cellular activity. We advance UNC10245131, a cyclic peptide with low nanomolar affinity and good selectivity for CIB1 over other EF-hand domain proteins and improved permeability and stability over previously identified linear peptide inhibitor UNC10245092. Unlike UNC10245092, UNC10245131 lacks cytotoxicity and does not affect downstream signaling. Despite this, UNC10245131 is a potent ligand that could aid in clarifying roles of CIB1 in TNBC survival and proliferation and other CIB1-associated biological phenotypes
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
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