10,679 research outputs found
Problems with Extraction of the Nucleon to Delta(1232) Photonic Amplitudes
We investigate the model dependence and the importance of choice of database
in extracting the {\it physical} nucleon-Delta(1232) electromagnetic transition
amplitudes, of interest to QCD and baryon structure, from the pion
photoproduction observables. The model dependence is found to be much smaller
than the range of values obtained when different datasets are fitted. In
addition, some inconsistencies in the current database are discovered, and
their affect on the extracted transition amplitudes is discussed.Comment: Revtex, 2 figs., submitted to PR
Optically-Induced Polarons in Bose-Einstein Condensates: Monitoring Composite Quasiparticle Decay
Nonresonant light-scattering off atomic Bose-Einstein condensates (BECs) is
predicted to give rise to hitherto unexplored composite quasiparticles:
unstable polarons, i.e., local ``impurities'' dressed by virtual phonons.
Optical monitoring of their spontaneous decay can display either Zeno or
anti-Zeno deviations from the Golden Rule, and thereby probe the temporal
correlations of elementary excitations in BECs.Comment: 4 pages, 3 figure
Density-Matrix Spectra of Solvable Fermionic Systems
We consider non-interacting fermions on a lattice and give a general result
for the reduced density matrices corresponding to parts of the system. This
allows to calculate their spectra, which are essential in the DMRG method, by
diagonalizing small matrices. We discuss these spectra and their typical
features for various fermionic quantum chains and for the two-dimensional
tight-binding model.Comment: 12 pages and 9 figure
Reconstructing Seesaws
We explore some aspects of "reconstructing" the heavy singlet sector of
supersymmetric type I seesaw models, for two, three or four singlets. We work
in the limit where one light neutrino is massless. In an ideal world, where
selected coefficients of the TeV-scale effective Lagrangian could be measured
with arbitrary accuracy, the two-singlet case can be reconstructed, two three
or more singlets can be differentiated, and an inverse seesaw with four
singlets can be reconstructed. In a more realistic world, we estimate \ell_\a
\to \ell_\b \gamma expectations with a "Minimal-Flavour-Violation-like"
ansatz, which gives a relation between ratios of the three branching ratios.
The two singlet model predicts a discrete set of ratios.Comment: 14 page
Kaon photoproduction: background contributions, form factors and missing resonances
The photoproduction p(gamma, K+)Lambda process is studied within a
field-theoretic approach. It is shown that the background contributions
constitute an important part of the reaction dynamics. We compare predictions
obtained with three plausible techniques for dealing with these background
contributions. It appears that the extracted resonance parameters drastically
depend on the applied technique. We investigate the implications of the
corrections to the functional form of the hadronic form factor in the contact
term, recently suggested by Davidson and Workman (Phys. Rev. C 63, 025210). The
role of background contributions and hadronic form factors for the
identification of the quantum numbers of ``missing'' resonances is discussed.Comment: 11 pages, 7 eps figures, submitted to Phys. Rev.
Rippled Cosmological Dark Matter from Damped Oscillating Newton Constant
Let the reciprocal Newton 'constant' be an apparently non-dynamical
Brans-Dicke scalar field damped oscillating towards its General Relativistic
VEV. We show, without introducing additional matter fields or dust, that the
corresponding cosmological evolution averagely resembles, in the Jordan frame,
the familiar dark radiation -> dark matter -> dark energy domination sequence.
The fingerprints of our theory are fine ripples, hopefully testable, in the FRW
scale factor; they die away at the General Relativity limit. The possibility
that the Brans-Dicke scalar also serves as the inflaton is favorably examined.Comment: RevTex4, 12 pages, 5 figures; Minor revision, References adde
Simulation of adiabatic thermal beams in a periodic solenoidal magnetic focusing field
Self-consistent particle-in-cell simulations are performed to verify earlier theoretical predictions of adiabatic thermal beams in a periodic solenoidal magnetic focusing field [ K. R. Samokhvalova, J. Zhou and C. Chen Phys. Plasmas 14 103102 (2007); J. Zhou, K. R. Samokhvalova and C. Chen Phys. Plasmas 15 023102 (2008)]. In particular, results are obtained for adiabatic thermal beams that do not rotate in the Larmor frame. For such beams, the theoretical predictions of the rms beam envelope, the conservations of the rms thermal emittances, the adiabatic equation of state, and the Debye length are verified in the simulations. Furthermore, the adiabatic thermal beam is found be stable in the parameter regime where the simulations are performed.United States. Dept. of Energy (Grant DEFG02- 95ER40919)United States. Dept. of Energy (Grant DE-FG02-05ER54836
Hybridized Affleck-Dine baryogenesis
We propose a novel scenario for Affleck-Dine baryogenesis in the braneworld,
considering the hybrid potential for the Affleck-Dine field. Destabilization of
the flat direction is not due to the Hubble parameter, but is induced by a
trigger field. The moduli for the brane distance plays the role of the trigger
field. Q-balls are unstable in models with large extra dimensions.Comment: 10pages, plain latex2e, references added, to appear in PR
Impact of tumour histological subtype on chemotherapy outcome in advanced oesophageal cancer.
AIM: To investigate the impact of histology on outcome in advanced oesophageal cancer treated with first-line fluoropyrimidine-based chemotherapy. METHODS: Individual patient data were pooled from three randomised phase III trials of fluoropyrimidine-based chemotherapy ± platinum/anthracycline in patients with advanced, untreated gastroesophageal adenocarcinoma or squamous cell carcinoma (SCC) randomised between 1994 and 2005. The primary endpoint was overall survival of oesophageal cancer patients according to histology. Secondary endpoints were response rates and a toxicity composite endpoint. RESULTS: Of the total 1836 randomised patients, 973 patients (53%) were eligible (707 patients with gastric cancer were excluded), 841 (86%) had adenocarcinoma and 132 (14%) had SCC. There was no significant difference in survival between patients with adenocarcinoma and SCC, with median overall survivals of 9.5 mo vs 7.6 mo (HR = 0.85, 95%CI: 0.70-1.03, P = 0.09) and one-year survivals of 38.8% vs 28.2% respectively. The overall response rate to chemotherapy was 44% for adenocarcinoma vs 33% for SCC (P = 0.01). There was no difference in the frequency of the toxicity composite endpoint between the two groups. CONCLUSION: There was no significant difference in survival between adenocarcinoma and SCC in patients with advanced oesophageal cancer treated with fluoropyrimidine-based chemotherapy despite a trend for worse survival and less chemo-sensitivity in SCC. Tolerance to treatment was similar in both groups. This analysis highlights the unmet need for SCC-specific studies in advanced oesophageal cancer and will aid in the design of future trials of targeted agents
Supersymmetry Breaking in the Early Universe
Supersymmetry breaking in the early universe induces scalar soft potentials
with curvature of order the Hubble constant. This has a dramatic effect on the
coherent production of scalar fields along flat directions. For the moduli
problem it generically gives a concrete realization of the problem by
determining the field value subsequent to inflation. However it might suggest a
solution if the minimum of the induced potential coincides with the true
minimum. The induced Hubble scale mass also has important implications for the
Affleck-Dine mechanism of baryogenesis. This mechanism requires large squark or
slepton expectation values to develop along flat directions in the early
universe. This is generally not the case if the induced mass squared is
positive, but does occur if it is negative. The resulting baryon to entropy
ratio depends mainly on the dimension of the nonrenormalizable operator in the
superpotential which stabilizes the flat direction, and the reheat temperature
after inflation. Unlike the original scenario, it is possible to obtain an
acceptable baryon asymmetry without subsequent entropy releases.Comment: 11 pages, requires phyzz
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