1,920 research outputs found
Statistical thermodynamics for a non-commutative special relativity: Emergence of a generalized quantum dynamics
There ought to exist a description of quantum field theory which does not
depend on an external classical time. To achieve this goal, in a recent paper
we have proposed a non-commutative special relativity in which space-time and
matter degrees of freedom are treated as classical matrices with arbitrary
commutation relations, and a space-time line element is defined using a trace.
In the present paper, following the theory of Trace Dynamics, we construct a
statistical thermodynamics for the non-commutative special relativity, and show
that one arrives at a generalized quantum dynamics in which space and time are
non-classical and have an operator status. In a future work, we will show how
standard quantum theory on a classical space-time background is recovered from
here.Comment: 21 pages. arXiv admin note: text overlap with arXiv:1106.091
High-Temperature Series Analyses of the Classical Heisenberg and XY Model
Although there is now a good measure of agreement between Monte Carlo and
high-temperature series expansion estimates for Ising () models, published
results for the critical temperature from series expansions up to 12{\em th}
order for the three-dimensional classical Heisenberg () and XY ()
model do not agree very well with recent high-precision Monte Carlo estimates.
In order to clarify this discrepancy we have analyzed extended high-temperature
series expansions of the susceptibility, the second correlation moment, and the
second field derivative of the susceptibility, which have been derived a few
years ago by L\"uscher and Weisz for general vector spin models on
-dimensional hypercubic lattices up to 14{\em th} order in . By analyzing these series expansions in three dimensions with two different
methods that allow for confluent correction terms, we obtain good agreement
with the standard field theory exponent estimates and with the critical
temperature estimates from the new high-precision MC simulations. Furthermore,
for the Heisenberg model we reanalyze existing series for the susceptibility on
the BCC lattice up to 11{\em th} order and on the FCC lattice up to 12{\em th}
order.Comment: 15 pages, Latex, 2 PS figures not included. FUB-HEP 18/92 and HLRZ
76/9
Photon Splitting in a Strong Magnetic Field: Recalculation and Comparison With Previous Calculations
We recalculate the amplitude for photon splitting in a strong magnetic field
below the pair production threshold, using the worldline path integral variant
of the Bern--Kosower formalism. Numerical comparison (using programs that we
have made available for public access on the Internet) shows that the results
of the recalculation are identical to the earlier calculations of Adler and
later of Stoneham, and to the recent recalculation by Baier, Milstein, and
Shaisultanov.Comment: Revtex, 9 pages, no figure
On Di\'osi-Penrose criterion of gravity-induced quantum collapse
It is shown that the Di\'osi-Penrose criterion of gravity-induced quantum
collapse may be inconsistent with the discreteness of space-time, which is
generally considered as an indispensable element in a complete theory of
quantum gravity. Moreover, the analysis also suggests that the discreteness of
space-time may result in rapider collapse of the superposition of energy
eigenstates than required by the Di\'osi-Penrose criterion.Comment: 5 pages, no figure
Behavioural responses of Callosobruchus maculatus to volatiles organic compounds found in the headspace of dried green pea seeds: Poster
Two-Loop Euler-Heisenberg QED Pair-Production Rate
We study the divergence of large-order perturbation theory in the worldline
expression for the two-loop Euler-Heisenberg QED effective Lagrangian in a
constant magnetic field. The leading rate of divergence is identical, up to an
overall factor, to that of the one-loop case. From this we deduce, using Borel
summation techniques, that the leading behaviour of the imaginary part of the
two-loop effective Lagrangian for a constant E field, giving the
pair-production rate, is proportional to the one-loop result. This also serves
as a test of the mass renormalization, and confirms the earlier analysis by
Ritus.Comment: 12 pages, 5 figure
Moist Orographic Convection: Physical Mechanisms and Links to Surface-Exchange Processes
This paper reviews the current understanding of moist orographic convection and its regulation by surface-exchange processes. Such convection tends to develop when and where moist instability coincides with sufficient terrain-induced ascent to locally overcome convective inhibition. The terrain-induced ascent can be owing to mechanical (airflow over or around an obstacle) and/or thermal (differential heating over sloping terrain) forcing. For the former, the location of convective initiation depends on the dynamical flow regime. In “unblocked” flows that ascend the barrier, the convection tends to initiate over the windward slopes, while in “blocked” flows that detour around the barrier, the convection tends to initiate upstream and/or downstream of the high terrain where impinging flows split and rejoin, respectively. Processes that destabilize the upstream flow for mechanically forced moist convection include large-scale moistening and ascent, positive surface sensible and latent heat fluxes, and differential advection in baroclinic zones. For thermally forced flows, convective initiation is driven by thermally direct circulations with sharp updrafts over or downwind of the mountain crest (daytime) or foot (nighttime). Along with the larger-scale background flow, local evapotranspiration and transport of moisture, as well as thermodynamic heterogeneities over the complex terrain, regulate moist instability in such events. Longstanding limitations in the quantitative understanding of related processes, including both convective preconditioning and initiation, must be overcome to improve the prediction of this convection, and its collective effects, in weather and climate models. View Full-Tex
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