507 research outputs found
A New Finite-lattice study of the Massive Schwinger Model
A new finite lattice calculation of the low lying bound state energies in the
massive Schwinger model is presented, using a Hamiltonian lattice formulation.
The results are compared with recent analytic series calculations in the low
mass limit, and with a new higher order non-relativistic series which we
calculate for the high mass limit. The results are generally in good agreement
with these series predictions, and also with recent calculations by light cone
and related techniques
Transient two-dimensional electronic spectroscopy: coherent dynamics at arbitrary times along the reaction coordinate
Recent advances in two-dimensional electronic spectroscopy (2DES) have enabled identification of fragile quantum coherences in condensed-phase systems near the equilibrium molecular geometry. In general, traditional 2DES cannot measure such coherences associated with photophysical processes that occur at times significantly after the initially prepared state has dephased, such as the evolution of the initial excited state into a charge transfer state. We demonstrate the use of transient two-dimensional electronic spectroscopy (t-2DES) to probe coherences in an electron donorâacceptor dyad consisting of a perylenediimide (PDI) acceptor and a perylene (Per) donor. An actinic pump pulse prepares the lowest excited singlet state of PDI followed by formation of the PDIâąââPerâą+ ion pair, which is probed at different times following the actinic pulse using 2DES. Analysis of the observed coherences provides information about electronic, vibronic, and vibrational interactions at any time along the reaction coordinate for ion pair formation
Interpreting OPERA results on superluminal neutrino
OPERA has claimed the discovery of superluminal propagation of neutrinos. We
analyze the consistency of this claim with previous tests of special
relativity. We find that reconciling the OPERA measurement with information
from SN1987a and from neutrino oscillations requires stringent conditions. The
superluminal limit velocity of neutrinos must be nearly flavor independent,
must decrease steeply in the low-energy domain, and its energy dependence must
depart from a simple power law. We construct illustrative models that satisfy
these conditions, by introducing Lorentz violation in a sector with light
sterile neutrinos. We point out that, quite generically, electroweak quantum
corrections transfer the information of superluminal neutrino properties into
Lorentz violations in the electron and muon sector, in apparent conflict with
experimental data.Comment: 21 pages, 4 figures. Final version to appear on NPB. The electroweak
corrections that transfer Lorentz violation from neutrinos to electrons have
now been computed finding a result in agreement with the estimate in the
first version of the pape
The (1+1)-dimensional Massive sine-Gordon Field Theory and the Gaussian Wave-functional Approach
The ground, one- and two-particle states of the (1+1)-dimensional massive
sine-Gordon field theory are investigated within the framework of the Gaussian
wave-functional approach. We demonstrate that for a certain region of the
model-parameter space, the vacuum of the field system is asymmetrical.
Furthermore, it is shown that two-particle bound state can exist upon the
asymmetric vacuum for a part of the aforementioned region. Besides, for the
bosonic equivalent to the massive Schwinger model, the masses of the one boson
and two-boson bound states agree with the recent second-order results of a
fermion-mass perturbation calculation when the fermion mass is small.Comment: Latex, 11 pages, 8 figures (EPS files
Variational Mass Perturbation Theory for Light-Front Bound-State Equations
We investigate the mesonic light-front bound-state equations of the 't Hooft
and Schwinger model in the two-particle, i.e. valence sector, for small fermion
mass. We perform a high precision determination of the mass and light-cone wave
function of the lowest lying meson by combining fermion mass perturbation
theory with a variational approach. All calculations are done entirely in the
fermionic representation without using any bosonization scheme. In a
step-by-step procedure we enlarge the space of variational parameters. For the
first two steps, the results are obtained analytically. Beyond that we use
computer algebraic and numerical methods. We achieve good convergence so that
the calculation of the meson mass squared can be extended to third order in the
fermion mass. Within the numerical treatment we include higher Fock states up
to six particles. Our results are consistent with all previous numerical
investigations, in particular lattice calculations. For the massive Schwinger
model, we find a small discrepancy (less than 2 percent) in comparison with
known bosonization results. Possible resolutions of this discrepancy are
discussed.Comment: some points clarified, representation straightened, to appear in
Phys. Rev. D, 31 pages, Latex, REVTeX, epsfig, 3 postscript figures include
Hilbert space of wormholes
Wormhole boundary conditions for the Wheeler--DeWitt equation can be derived
from the path integral formulation. It is proposed that the wormhole wave
function must be square integrable in the maximal analytic extension of
minisuperspace. Quantum wormholes can be invested with a Hilbert space
structure, the inner product being naturally induced by the minisuperspace
metric, in which the Wheeler--DeWitt operator is essentially self--adjoint.
This provides us with a kind of probabilistic interpretation. In particular,
giant wormholes will give extremely small contributions to any wormhole state.
We also study the whole spectrum of the Wheeler--DeWitt operator and its role
in the calculation of Green's functions and effective low energy interactions.Comment: 23 pages, 2 figures available upon request, REVTE
Dual embedding of the Lorentz-violating electrodinamics and Batalin-Vilkovisky quantization
Modifications of the electromagnetic Maxwell Lagrangian in four dimensions
have been considered by some authors. One may include an explicit massive term
(Proca) and a topological but not Lorentz-invariant term within certain
observational limits.
We find the dual-corresponding gauge invariant version of this theory by
using the recently suggested gauge embedding method. We enforce this
dualisation procedure by showing that, in many cases, this is actually a
constructive method to find a sort of parent action, which manifestly
establishes duality. We also use the gauge invariant version of this theory to
formulate a Batalin-Vilkovisky quantization and present a detailed discussion
on the excitation spectrum.Comment: 8 page
On the Resummed Hadronic Spectra of Inclusive B Decays
In this paper we investigate the hadronic mass spectra of inclusive B decays.
Specifically, we study how an upper cut on the invariant mass spectrum, which
is necessary to extract V_{ub}, results in the breakdown of the standard
perturbative expansion due to the existence of large infrared logs. We first
show how the decay rate factorizes at the level of the double differential
distribution. Then, we present closed form expressions for the resummed cut
rate for the inclusive decays B -> X_s gamma and B -> X_u e nu at
next-to-leading order in the infrared logs. Using these results, we determine
the range of cuts for which resummation is necessary, as well as the range for
which the resummed expansion itself breaks down. We also use our results to
extract the leading and next to leading infrared log contribution to the two
loop differential rate. We find that for the phenomenologically interesting cut
values, there is only a small region where the calculation is under control.
Furthermore, the size of this region is sensitive to the parameter
\bar{\Lambda}. We discuss the viability of extracting V_{ub} from the hadronic
mass spectrum.Comment: 18 pages, 5 figures, minor change
OGFOD1 catalyzes prolyl hydroxylation of RPS23 and is involved in translation control and stress granule formation
2-Oxoglutarate (2OG) and Fe(II)-dependent oxygenase domain-containing protein 1 (OGFOD1) is predicted to be a conserved 2OG oxygenase, the catalytic domain of which is related to hypoxia-inducible factor prolyl hydroxylases. OGFOD1 homologs in yeast are implicated in diverse cellular functions ranging from oxygen-dependent regulation of sterol response genes (Ofd1, Schizosaccharomyces pombe) to translation termination/mRNA polyadenylation (Tpa1p, Saccharomyces cerevisiae). However, neither the biochemical activity of OGFOD1 nor the identity of its substrate has been defined. Here we show that OGFOD1 is a prolyl hydroxylase that catalyzes the posttranslational hydroxylation of a highly conserved residue (Pro-62) in the small ribosomal protein S23 (RPS23). Unusually OGFOD1 retained a high affinity for, and forms a stable complex with, the hydroxylated RPS23 substrate. Knockdown or inactivation of OGFOD1 caused a cell type-dependent induction of stress granules, translational arrest, and growth impairment in a manner complemented by wild-type but not inactive OGFOD1. The work identifies a human prolyl hydroxylase with a role in translational regulation
Outcome following surgery for colorectal cancer: analysis by hospital after adjustment for case-mix and deprivation
Outcome, adjusted for case-mix and deprivation, in 3200 patients undergoing resection for colorectal cancer in 11 hospitals in Central Scotland between 1991 and 1994 was studied. There were significant differences among individual hospitals in the proportion of elderly (P<0.001) and deprived (P<0.0001) patients, the mode (P=0.007) and stage (P<0.0001) at presentation, and the proportion of patients who underwent apparently curative resection (P<0.001). There were no significant differences in postoperative mortality. Cancer-specific survival at 5 years following apparently curative resection varied from 59 to 76%; cancer-specific survival at 2 years following palliative resection varied from 22 to 44%. The corresponding hazard ratios, adjusted for the above prognostic factors, for patients undergoing apparently curative resection varied among hospitals from 0.58 to 1.32; and the ratios for palliative resection varied from 0.73 to 1.26. This study demonstrates that, after adjustment for variations in case-mix and deprivation, significant differences in outcome among hospitals following resection for colorectal cancer persist
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