6,202 research outputs found
Causal signal transmission by quantum fields. IV: The causal Wick theorem
Wick's theorem in the Schwinger-Perel-Keldysh closed-time-loop formalism is
written in a form where the place of contractions is taken by the linear
response function of the field. This result demonstrates that the physical
information supplied by Wick's theorem for operators is propagation of the free
field in space and time.Comment: Final version, to appear in Phys Rev
Experimental study of direct photon emission in K- --> pi- pi0 gamma decay using ISTRA+ detector
The branching ratio in the charged-pion kinetic energy region of 55 to 90 MeV
for the direct photon emission in the K- --> pi- pi0 gamma decay has been
measured using in-flight decays detected with the ISTRA+ setup operating in the
25 GeV/c negative secondary beam of the U-70 PS. The value
Br(DE)=[0.37+-0.39(stat)+-0.10(syst)]*10^(-5) obtained from the analysis of 930
completely reconstructed events is consistent with the average value of two
stopped-kaon experiments, but it differs by 2.5 standard deviations from the
average value of three in-flight-kaon experiments. The result is also compared
with recent theoretical predictions.Comment: 13 pages, 8 figure
Thermal drag revisited: Boltzmann versus Kubo
The effect of mutual drag between phonons and spin excitations on the thermal
conductivity of a quantum spin system is discussed. We derive general
expression for the drag component of the thermal current using both Boltzmann
equation approach and Kubo linear-response formalism to leading order in the
spin-phonon coupling. We demonstrate that aside from higher-order corrections
which appear in the Kubo formalism both approaches yield identical results for
the drag thermal conductivity. We discuss the range of applicability of our
result and provide a generalization of our consideration to the cases of
fermionic excitations and to anomalous forms of boson-phonon coupling. Several
asymptotic regimes of our findings relevant to realistic situations are
highlighted.Comment: 14 pages, 3 figures, published version, extended discussio
Tunka-Rex: the Cost-Effective Radio Extension of the Tunka Air-Shower Observatory
Tunka-Rex is the radio extension of the Tunka cosmic-ray observatory in
Siberia close to Lake Baikal. Since October 2012 Tunka-Rex measures the radio
signal of air-showers in coincidence with the non-imaging air-Cherenkov array
Tunka-133. Furthermore, this year additional antennas will go into operation
triggered by the new scintillator array Tunka-Grande measuring the secondary
electrons and muons of air showers. Tunka-Rex is a demonstrator for how
economic an antenna array can be without losing significant performance: we
have decided for simple and robust SALLA antennas, and we share the existing
DAQ running in slave mode with the PMT detectors and the scintillators,
respectively. This means that Tunka-Rex is triggered externally, and does not
need its own infrastructure and DAQ for hybrid measurements. By this, the
performance and the added value of the supplementary radio measurements can be
studied, in particular, the precision for the reconstructed energy and the
shower maximum in the energy range of approximately eV. Here
we show first results on the energy reconstruction indicating that radio
measurements can compete with air-Cherenkov measurements in precision.
Moreover, we discuss future plans for Tunka-Rex.Comment: Proceeding of UHECR 2014, Springdale, Utah, USA, accepted by JPS
Conference Proceeding
One- and two-photon resonant spectroscopy of hydrogen and anti-hydrogen atoms in external electric fields
The resonant spectra of hydrogen and anti-hydrogen atoms in the presence of
an external electric field are compared theoretically. It is shown that
nonresonant corrections to the transition frequency contain terms linear in the
electric field. The existence of these terms does not violate space and time
parity and leads to a difference in the resonant spectroscopic measurements for
hydrogen and anti-hydrogen atoms in an external electric field. The one-photon
1s-2p and the two-photon 1s-2s resonances are investigated
Fermion confinement induced by geometry
We consider a five-dimensional model in which fermions are confined in a
hypersurface due to an interaction with a purely geometric field. Inspired by
the Rubakov-Shaposhnikov field-theoretical model, in which massless fermions
can be localized in a domain wall through the interaction of a scalar field, we
show that particle confinement may also take place if we endow the
five-dimensional bulk with a Weyl integrable geometric structure, or if we
assume the existence of a torsion field acting in the bulk. In this picture,
the kind of interaction considered in the Rubakov-Shaposhnikov model is
replaced by the interaction of fermions with a geometric field, namely a Weyl
scalar field or a torsion field. We show that in both cases the confinement is
independent of the energy and the mass of the fermionic particle. We generalize
these results to the case in which the bulk is an arbitrary n-dimensional
curved space.Comment: 8 page
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