1,227 research outputs found
S-Track Stabilization of Heterotic de Sitter Vacua
We present a new mechanism, the S-Track, to stabilize the volume modulus S in
heterotic M-theory flux compactifications along with the orbifold-size T
besides complex structure and vector bundle moduli stabilization. The key
dynamical ingredient which makes the volume modulus stabilization possible, is
M5-instantons arising from M5-branes wrapping the whole Calabi-Yau slice. These
are natural in heterotic M-theory where the warping shrinks the Calabi-Yau
volume along S^1/Z_2. Combined with H-flux, open M2-instantons and hidden
sector gaugino condensation it leads to a superpotential W which stabilizes S
similar like a racetrack but without the need for multi gaugino condensation.
Moreover, W contains two competing non-perturbative effects which stabilize T.
We analyze the potential and superpotentials to show that it leads to heterotic
de Sitter vacua with broken supersymmetry through non-vanishing F-terms.Comment: 16 pages, 2 figures; final PRD versio
Rotational Effects of Twisted Light on Atoms Beyond the Paraxial Approximation
The transition probability for the emission of a Bessel photon by an atomic
system is calculated within first order perturbation theory. We derive a closed
expression for the electromagnetic potentials beyond the paraxial approximation
that permits a systematic multipole approximation . The matrix elements between
center of mass and internal states are evaluated for some specially relevant
cases. This permits to clarify the feasibility of observing the rotational
effects of twisted light on atoms predicted by the calculations. It is shown
that the probability that the internal state of an atom acquires orbital
angular momentum from light is, in general, maximum for an atom located at the
axis of a Bessel mode. For a Gaussian packet, the relevant parameter is the
ratio of the spread of the atomic center of mass wave packet to the transversal
wavelength of the photon.Comment: 10 pages, no figure
A study of Feshbach resonances and the unitary limit in a model of strongly correlated nucleons
A model of strongly interacting and correlated hadrons is developed. The
interaction used contains a long range attraction and short range repulsive
hard core. Using this interaction and various limiting situations of it, a
study of the effect of bound states and Feshbach resonances is given. The
limiting situations are a pure square well interaction, a delta-shell potential
and a pure hard core potential. The limit of a pure hard core potential are
compared with results for a spinless Bose and Fermi gas. The limit of many
partial waves for a pure hard core interaction is also considered and result in
expressions involving the hard core volume. This feature arises from a scaling
relation similar to that for hard sphere scattering with diffractive
corrections. The role of underlying isospin symmetries associated with the
strong interaction of protons and neutrons in this two component model is
investigated. Properties are studied with varying proton fraction. An analytic
expression for the Beth Uhlenbeck continuum integral is developed which closely
approximates exact results based on the potential model considered. An analysis
of features associated with a unitary limit is given. In the unitary limit of
very large scattering length, the ratio of effective range to thermal
wavelength appears as a limiting scale. Thermodynamic quantities such as the
entropy and compressibility are also developed. The effective range corrections
to the entropy vary as the cube of this ratio for low temperatures and are
therefore considerably reduced compared to the corrections to the interaction
energy which varies linearly with this ratio. Effective range corrections to
the compressibility are also linear in the ratio.Comment: 39 pages, 15 figures, 2 table
Non-Abelian Dipole Radiation and the Heavy Quark Expansion
Dipole radiation in QCD is derived to the second order in . A
power-like evolution of the spin-singlet heavy quark operators is obtained to
the same accuracy. In particular, relation between a
short-distance low-scale running heavy quark mass and the \barMS mass is
given. We discuss the properties of the effective QCD coupling \aw(E) which
governs the dipole radiation. This coupling is advantageous for heavy quark
physics.Comment: 12 pages, Late
Signatures of High-Intensity Compton Scattering
We review known and discuss new signatures of high-intensity Compton
scattering assuming a scenario where a high-power laser is brought into
collision with an electron beam. At high intensities one expects to see a
substantial red-shift of the usual kinematic Compton edge of the photon
spectrum caused by the large, intensity dependent, effective mass of the
electrons within the laser beam. Emission rates acquire their global maximum at
this edge while neighbouring smaller peaks signal higher harmonics. In
addition, we find that the notion of the centre-of-mass frame for a given
harmonic becomes intensity dependent. Tuning the intensity then effectively
amounts to changing the frame of reference, going continuously from inverse to
ordinary Compton scattering with the centre-of-mass kinematics defining the
transition point between the two.Comment: 25 pages, 16 .eps figure
Model Analysis of the Electroproduction Reaction on the Proton
Recent CLAS data on the electroproduction off protons at
1.3W1.57 GeV and 0.250.6 GeV have been analyzed using
a meson-baryon phenomenological model. By fitting nine 1-fold differential
cross section data for each and bin, the charged double pion
electroproduction mechanisms are identified from their manifestations in the
observables. We have extracted the cross sections from amplitudes of each of
the considered isobar channels as well as from their coherent sum. We also
obtained non-resonant partial wave amplitudes of all contributing isobar
channels which could be useful for advancing a complete coupled-channel
analysis of all meson electroproduction data.Comment: Experiment Numbers: E93-006, E94-005 Group: Hall
A search for J^{PC}=1^{-+} exotic mesons in the pi- pi- pi+ and pi- pi0 pi0 systems
A partial wave analysis (PWA) of the pi-pi-pi+ and pi-pi0pi0 systems produced
in the reaction pi- p -> (3pi)-p at 18 GeV/c was carried out using an isobar
model assumption. This analysis is based on 3.0M pi-pi0pi0 events and 2.6M
pi-pi-pi+ events and shows production of the a2(1320), pi2(1670) and \pi(1800)
mesons. An earlier analysis of 250K pi-pi-pi+ events from the same experiment
showed possible evidence for a J^{PC}=1^{-+}$ exotic meson with a mass of 1.6
GeV/c^2 decaying into rho pi. In this analysis of a higher statistics sample of
the (3pi)- system in two charged modes we find no evidence of an exotic meson.Comment: 4 pages, 5 figures, added comment about the negative reflectivity
exotic wave
Emergence of Oscillons in an Expanding Background
We consider a (1+1) dimensional scalar field theory that supports oscillons,
which are localized, oscillatory, stable solutions to nonlinear equations of
motion. We study this theory in an expanding background and show that oscillons
now lose energy, but at a rate that is exponentially small when the expansion
rate is slow. We also show numerically that a universe that starts with
(almost) thermal initial conditions will cool to a final state where a
significant fraction of the energy of the universe -- on the order of 50% -- is
stored in oscillons. If this phenomenon persists in realistic models, oscillons
may have cosmological consequences.Comment: 13 pages, 4 .eps figures, uses RevTeX4; v2: clarified details of
expansion, added reference
Viral uncoating is directional: exit of the genomic RNA in a common cold virus starts with the poly-(A) tail at the 3′-end
Upon infection, many RNA viruses reorganize their capsid for release of the genome into the host cell cytosol for replication. Often, this process is triggered by receptor binding and/or by the acidic environment in endosomes. In the genus Enterovirus, which includes more than 150 human rhinovirus (HRV) serotypes causing the common cold, there is persuasive evidence that the viral RNA exits single-stranded through channels formed in the protein shell. We have determined the time-dependent emergence of the RNA ends from HRV2 on incubation of virions at 56°C using hybridization with specific oligonucleotides and detection by fluorescence correlation spectroscopy. We report that psoralen UV crosslinking prevents complete RNA release, allowing for identification of the sequences remaining inside the capsid. We also present the structure of uncoating intermediates in which parts of the RNA are condensed and take the form of a rod that is directed roughly towards a two-fold icosahedral axis, the presumed RNA exit point. Taken together, in contrast to schemes frequently depicted in textbooks and reviews, our findings demonstrate that exit of the RNA starts from the 3′-end. This suggests that packaging also occurs in an ordered manner resulting in the 3′-poly-(A) tail becoming located close to a position of pore formation during conversion of the virion into a subviral particle. This directional genome release may be common to many icosahedral non-enveloped single-stranded RNA viruse
Nonlocal Electrodynamics of Rotating Systems
The nonlocal electrodynamics of uniformly rotating systems is presented and
its predictions are discussed. In this case, due to paucity of experimental
data, the nonlocal theory cannot be directly confronted with observation at
present. The approach adopted here is therefore based on the correspondence
principle: the nonrelativistic quantum physics of electrons in circular
"orbits" is studied. The helicity dependence of the photoeffect from the
circular states of atomic hydrogen is explored as well as the resonant
absorption of a photon by an electron in a circular "orbit" about a uniform
magnetic field. Qualitative agreement of the predictions of the classical
nonlocal electrodynamics with quantum-mechanical results is demonstrated in the
correspondence regime.Comment: 23 pages, no figures, submitted for publicatio
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