225 research outputs found
The Green--Schwarz Superstring in Extended Configuration Space and Infinitely Reducible First Class Constraints Problem
The Green--Schwarz superstring action is modified to include some set of
additional (on-shell trivial) variables. A complete constraints system of the
theory turns out to be reducible both in the original and in additional
variable sectors. The initial first class constraints and second
class ones are shown to be unified with first and second class
constraints from the additional variables sector, resulting with
-covariant and linearly independent constraint sets. Residual
reducibility proves to fall on second class constraints only.Comment: 14 pages, LaTe
Phase diagram of the extended Hubbard chain with charge-dipole interactions
We consider a modified extended Hubbard model (EHM) which, in addition to the
on-site repulsion U and nearest-neighbor repulsion V, includes polarization
effects in second-order perturbation theory. The model is equivalent to an EHM
with renormalized U plus a next-nearest-neighbor repulsion term. Using a method
based on topological quantum numbers (charge and spin Berry phases), we
generalize to finite hopping t the quantum phase diagram in one dimension
constructed by van den Brink et al. (Phys. Rev. Lett. 75, 4658 (1995)). At
hopping t=0 there are two charge density-wave phases, one spin density-wave
phase and one intermediate phase with charge and spin ordering, depending on
the parameter values. At t \neq 0 the nature of each phase is confirmed by
studying correlation functions. However, in addition to the strong-coupling
phases, a small region with bond ordering appears. The region occupied by the
intermediate phase first increases and then decreases with increasing t, until
it finally disappears for t of the order but larger than U. For small t, the
topological transitions agree with the results of second order perturbation
theory.Comment: 6 pages, 5 figures, two columns latex version. Accepted for
publication in Physical Review B. Mistaken reference 16 has been correcte
Light-cone Superstring in AdS Space-time
We consider fixing the bosonic light-cone gauge for string in AdS in the
phase space framework, i.e. by choosing , and by choosing
so that is distributed uniformly (its density is independent of
). We discuss classical bosonic string in AdS space and superstring in
AdS_5 x S^5. In the latter case the starting point is the action found in
hep-th/0007036 where the kappa-symmetry is fixed by a fermionic light cone
gauge. We derive the light cone Hamiltonian in the AdS_5 x S^5 case and in the
case of superstring in AdS_3 x S^3. We also obtain a realization of the
generators of the basic symmetry superalgebra psu(2,2|4) in terms of the AdS_5
x S^5 superstring coordinate fields.Comment: 34 pages, latex. v3: section 5.4 revised. v4: minor corrections,
version to appear in NP
Aerosol chemical composition at Cabouw, The Netherlands as observed in two intensive periods in May 2008 and March 2009
Observations of aerosol chemical composition in Cabauw, the Netherlands, are presented for two intensive measurement periods in May 2008 and March 2009. Sub-micron aerosol chemical composition was measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and is compared to observations from aerosol size distribution measurements as well as composition measurements with a Monitor for AeRosol and GAses (MARGA) based instrument and a Thermal-Desorption Proton-Transfer-Reaction Mass-Spectrometer (TD-PTR-MS). An overview of the data is presented and the data quality is discussed. In May 2008 enhanced pollution was observed with organics contributing 40% to the PM1 mass. In contrast the observed average mass loading was lower in March 2009 and a dominance of ammonium nitrate (42%) was observed. The semi-volatile nature of ammonium nitrate is evident in the diurnal cycles with maximum concentrations observed in the morning hours in May 2008 and little diurnal variation observed in March 2009. Size dependent composition data from AMS measurements are presented and show a dominance of organics in the size range below 200 nm. A higher O:C ratio of the organics is observed for May 2008 than for March 2009. Together with the time series of individual tracer ions this shows the dominance of OOA over HOA in May 2008
CC chemokine receptor 2 is involved in intestinal homing of alloreactive donor CD8+ T cells during GVHD
The paradoxical effect of glucocorticoid-induced tumor necrosis factor receptor family-related gene (GITR) activation on alloreactive CD4 and CD8 T cells and the development of GVHD
Characteristic classes of gauge systems
We define and study invariants which can be uniformly constructed for any
gauge system. By a gauge system we understand an (anti-)Poisson supermanifold
provided with an odd Hamiltonian self-commuting vector field called a
homological vector field. This definition encompasses all the cases usually
included into the notion of a gauge theory in physics as well as some other
similar (but different) structures like Lie or Courant algebroids. For
Lagrangian gauge theories or Hamiltonian first class constrained systems, the
homological vector field is identified with the classical BRST transformation
operator. We define characteristic classes of a gauge system as universal
cohomology classes of the homological vector field, which are uniformly
constructed in terms of this vector field itself. Not striving to exhaustively
classify all the characteristic classes in this work, we compute those
invariants which are built up in terms of the first derivatives of the
homological vector field. We also consider the cohomological operations in the
space of all the characteristic classes. In particular, we show that the
(anti-)Poisson bracket becomes trivial when applied to the space of all the
characteristic classes, instead the latter space can be endowed with another
Lie bracket operation. Making use of this Lie bracket one can generate new
characteristic classes involving higher derivatives of the homological vector
field. The simplest characteristic classes are illustrated by the examples
relating them to anomalies in the traditional BV or BFV-BRST theory and to
characteristic classes of (singular) foliations.Comment: 23 pages, references added, typos correcte
Exactly solvable path integral for open cavities in terms of quasinormal modes
We evaluate the finite-temperature Euclidean phase-space path integral for
the generating functional of a scalar field inside a leaky cavity. Provided the
source is confined to the cavity, one can first of all integrate out the fields
on the outside to obtain an effective action for the cavity alone.
Subsequently, one uses an expansion of the cavity field in terms of its
quasinormal modes (QNMs)-the exact, exponentially damped eigenstates of the
classical evolution operator, which previously have been shown to be complete
for a large class of models. Dissipation causes the effective cavity action to
be nondiagonal in the QNM basis. The inversion of this action matrix inherent
in the Gaussian path integral to obtain the generating functional is therefore
nontrivial, but can be accomplished by invoking a novel QNM sum rule. The
results are consistent with those obtained previously using canonical
quantization.Comment: REVTeX, 26 pages, submitted to Phys. Rev.
The systematic study of the influence of neutron excess on the fusion cross sections using different proximity-type potentials
Using different types of proximity potentials, we have examined the trend of
variations of barrier characteristics (barrier height and its position) as well
as fusion cross sections for 50 isotopic systems including various collisions
of C, O, Mg, Si, S, Ca, Ar, Ti and Ni nuclei with condition
for compound systems. The results of our studies reveal that the relationships
between increase of barrier positions and decrease of barrier heights are both
linear with increase of ratio. Moreover, fusion cross sections also
enhance linearly with increase of this ratio.Comment: 28 pages, 7 figures, 5 Table
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