12,348 research outputs found
Quantized Maxwell Theory in a Conformally Invariant Gauge
Maxwell theory can be studied in a gauge which is invariant under conformal
rescalings of the metric, and first proposed by Eastwood and Singer. This paper
studies the corresponding quantization in flat Euclidean 4-space. The resulting
ghost operator is a fourth-order elliptic operator, while the operator P on
perturbations of the potential is a sixth-order elliptic operator. The operator
P may be reduced to a second-order non-minimal operator if a dimensionless
gauge parameter tends to infinity. Gauge-invariant boundary conditions are
obtained by setting to zero at the boundary the whole set of perturbations of
the potential, jointly with ghost perturbations and their normal derivative.
This is made possible by the fourth-order nature of the ghost operator. An
analytic representation of the ghost basis functions is also obtained.Comment: 8 pages, plain Tex. In this revised version, the calculation of ghost
basis functions has been amended, and the presentation has been improve
A new dielectric effect in viscous liquids
An accurate experimental and theoretical study has been performed about a
phenomenon, not previously reported in the literature, occurring in highly
viscous liquids: the formation of a definite pipe structure induced by the
passage of a heavy body, this structure lasting for quite a long time. A very
rich phenomenology (including mechanical, optical and structural effects)
associated with the formation of the pipe has been observed in different
liquids. Actually, the peculiar dynamical evolution of that structure does not
appear as a trivial manifestation of standard relaxation or spurious effects.
In particular we have revealed different time scales during the evolution of
the pipe and a non-monotonous decrease of the persistence time with decreasing
viscosity (with the appearance of at least two different maxima). We put
forward a microscopic model, consistent with the experimental data, where the
pipe behaves as a "dielectric shell" whose time evolution is described through
a simple thermodynamical approach, predicting several properties effectively
observed.Comment: 14 pages, 6 figures. arXiv admin note: text overlap with
arXiv:0812.436
Euclidean Maxwell Theory in the Presence of Boundaries. II
Zeta-function regularization is applied to complete a recent analysis of the
quantized electromagnetic field in the presence of boundaries. The quantum
theory is studied by setting to zero on the boundary the magnetic field, the
gauge-averaging functional and hence the Faddeev-Popov ghost field. Electric
boundary conditions are also studied. On considering two gauge functionals
which involve covariant derivatives of the 4-vector potential, a series of
detailed calculations shows that, in the case of flat Euclidean 4-space bounded
by two concentric 3-spheres, one-loop quantum amplitudes are gauge independent
and their mode-by-mode evaluation agrees with the covariant formulae for such
amplitudes and coincides for magnetic or electric boundary conditions. By
contrast, if a single 3-sphere boundary is studied, one finds some
inconsistencies, i.e. gauge dependence of the amplitudes.Comment: 24 pages, plain-tex, recently appearing in Classical and Quantum
Gravity, volume 11, pages 2939-2950, December 1994. The authors apologize for
the delay in circulating the file, due to technical problems now fixe
Essential self-adjointness in one-loop quantum cosmology
The quantization of closed cosmologies makes it necessary to study squared
Dirac operators on closed intervals and the corresponding quantum amplitudes.
This paper proves self-adjointness of these second-order elliptic operators.Comment: 14 pages, plain Tex. An Erratum has been added to the end, which
corrects section
Three Flavour Majorana Neutrinos with Magnetic Moments in a Supernova
The resonant transition effects MSW and NSFP for three flavour Majorana
neutrinos in a supernova are considered, where the transition magnetic moments
are likely to play a relevant role in neutrino physics. In this scenario, the
deformed thermal neutrino distributions are obtained for different choices of
the electron-tau mixing angle. Detailed predictions for the future large
neutrino detectors are also given in terms of the ratio between the spectra of
recoil electrons for deformed and undeformed spectra.Comment: 20 pages, LaTeX, 5 figures.p
Towards Dead Time Inclusion in Neuronal Modeling
A mathematical description of the refractoriness period in neuronal diffusion
modeling is given and its moments are explicitly obtained in a form that is
suitable for quantitative evaluations. Then, for the Wiener, Ornstein-Uhlenbeck
and Feller neuronal models, an analysis of the features exhibited by the mean
and variance of the first passage time and of refractoriness period is
performed.Comment: 12 pages, 1 figur
Spectral asymptotics of Euclidean quantum gravity with diff-invariant boundary conditions
A general method is known to exist for studying Abelian and non-Abelian gauge
theories, as well as Euclidean quantum gravity, at one-loop level on manifolds
with boundary. In the latter case, boundary conditions on metric perturbations
h can be chosen to be completely invariant under infinitesimal diffeomorphisms,
to preserve the invariance group of the theory and BRST symmetry. In the de
Donder gauge, however, the resulting boundary-value problem for the Laplace
type operator acting on h is known to be self-adjoint but not strongly
elliptic. The latter is a technical condition ensuring that a unique smooth
solution of the boundary-value problem exists, which implies, in turn, that the
global heat-kernel asymptotics yielding one-loop divergences and one-loop
effective action actually exists. The present paper shows that, on the
Euclidean four-ball, only the scalar part of perturbative modes for quantum
gravity are affected by the lack of strong ellipticity. Further evidence for
lack of strong ellipticity, from an analytic point of view, is therefore
obtained. Interestingly, three sectors of the scalar-perturbation problem
remain elliptic, while lack of strong ellipticity is confined to the remaining
fourth sector. The integral representation of the resulting zeta-function
asymptotics is also obtained; this remains regular at the origin by virtue of a
spectral identity here obtained for the first time.Comment: 25 pages, Revtex-4. Misprints in Eqs. (5.11), (5.14), (5.16) have
been correcte
Investigating Supergiant Fast X-ray Transients with LOFT
Supergiant Fast X-ray Transients (SFXT) are a class of High-Mass X-ray
Binaries whose optical counterparts are O or B supergiant stars, and whose
X-ray outbursts are ~ 4 orders of magnitude brighter than the quiescent state.
LOFT, the Large Observatory For X-ray Timing, with its coded mask Wide Field
Monitor (WFM) and its 10 m^2 class collimated X-ray Large Area Detector (LAD),
will be able to dramatically deepen the knowledge of this class of sources. It
will provide simultaneous high S/N broad-band and time-resolved spectroscopy in
several intensity states, and long term monitoring that will yield new
determinations of orbital periods, as well as spin periods. We show the results
of an extensive set of simulations performed using previous observational
results of these sources obtained with Swift and XMM-Newton. The WFM will
detect all SFXT flares within its field of view down to a 15-20 mCrab in 5ks.
Our simulations describe the outbursts at several intensities
(F_(2-10keV)=5.9x10^-9 to 5.5x10^-10 erg cm^-2 s^-1), the intermediate and most
common state (10^-11 erg cm^-2 s^-1), and the low state (1.2x10^-12 to 5x10^-13
erg cm^-2 s^-1). We also considered large variations of N_H and the presence of
emission lines, as observed by Swift and XMM-Newton.Comment: Proceedings of the 5th International Symposium on High-Energy
Gamma-Ray Astronomy (Gamma2012), Heidelberg. 4 pages, 3 figures, 1 tabl
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