656 research outputs found
Splitting of macroscopic fundamental strings in flat space and holographic hadron decays
In this review article we present the calculation of the splitting rate in
flat space of a macroscopic fundamental string either intersecting at a generic
angle a Dp-brane or lying on it. The result is then applied, in the context of
the string/gauge theory correspondence, to the study of exclusive decay rates
of large spin mesons into mesons. As examples, we discuss the cases of N=4 SYM
with a small number of flavors, and of QCD-like theories in the quenched
approximation. In the latter context, explicit analytic formulas are given for
decay rates of mesons formed either by heavy quarks or by massless quarks.Comment: 17 pages, 3 figures. Invited review for Modern Physics Letters
Structure and Metamorphism of the Talc Creek Area, Harrison Lake B.C.
The Slollicum and Cogburn terranes, metamorphosed country rock within the southern Coast Plutonic Complex, are juxtaposed along a thrust fault together with large slabs of ultramafic rock. The structure and metamorphism along and near this fault are the focus of this study.
Three periods of deformation (D1-D3) affected the study area. D1 structures consist of penetrative foliation and lineations that are attributed to thrust stacking of the Slollicum and Cogburn terranes. Foliation, which parallels the fault contact, dips to the northeast at moderate to steep angles. Lineations have mainly down-dip orientations. D2 structures record the intrusion of the Spuzzum pluton and consist of a foliation, defined mainly by biotite, that parallels the pluton contact. D3 caused rotation and distention of post-tectonic porphyroblasts during localized reactivation of the D1 foliation. D3 is probably a result of orogen-normal contraction that caused large map scale folding that affected the region some time after thrusting ceased.
The metamorphic grade increases to the northeast across the study area from greenschist to amphibolite facies. Three metamorphic events (M1-M3) affect the rocks in the study area. M1, associated with D1, resulted primarily in greenschist facies metamorphism. M2, a result of contact metamorphism from the Spuzzum intrusion, produced the index minerals biotite, hornblende and garnet. M3, a high pressure event, is characterized by an overprint of large garnet and radiating hornblende, which grew over the D1 foliation. These M3 porphyroblasts were then rotated or pulled apart suggesting D3 began after the peak of high pressure metamorphism. M3 also may have produced the randomly oriented hornblende that is observed on foliation surfaces of many Slollicum and Cogburn rocks. Terrane stacking must have taken place after 146 Ma, which is the U/Pb zircon age of the Slollicum rocks (Walker, in Bennett, 1989), and prior to the 96 Ma age (Brown and Walker, 1993) of the Spuzzum pluton
String splitting and strong coupling meson decay
We study the decay of high spin mesons using the gauge/string theory
correspondence. The rate of the process is calculated by studying the splitting
of a macroscopic string intersecting a D-brane. The result is applied to the
decay of mesons in N=4 SYM with a small number of flavors and in a gravity dual
of large N QCD. In QCD the decay of high spin mesons is found to be heavily
suppressed in the regime of validity of the supergravity description.Comment: 17 pages, 2 figures. V2: References added. V3: Minor correction
Thermal radiation in non-static curved spacetimes: quantum mechanical path integrals and configuration space topology
A quantum mechanical path integral derivation is given of a thermal
propagator in non-static Gui spacetime. The thermal nature of the propagator is
understood in terms of homotopically non-trivial paths in the configuration
space appropriate to tortoise coordinates. The connection to thermal emission
from collapsing black holes is discussed.Comment: 20 pages, major revised version, 9 figures, new titl
Massless particles on supergroups and AdS3 x S3 supergravity
Firstly, we study the state space of a massless particle on a supergroup with
a reparameterization invariant action. After gauge fixing the
reparameterization invariance, we compute the physical state space through the
BRST cohomology and show that the quadratic Casimir Hamiltonian becomes
diagonalizable in cohomology. We illustrate the general mechanism in detail in
the example of a supergroup target GL(1|1). The space of physical states
remains an indecomposable infinite dimensional representation of the space-time
supersymmetry algebra. Secondly, we show how the full string BRST cohomology in
the particle limit of string theory on AdS3 x S3 renders the quadratic Casimir
diagonalizable, and reduces the Hilbert space to finite dimensional
representations of the space-time supersymmetry algebra (after analytic
continuation). Our analysis provides an efficient way to calculate the
Kaluza-Klein spectrum for supergravity on AdS3 x S3. It may also be a step
towards the identification of an interesting and simpler subsector of
logarithmic supergroup conformal field theories, relevant to string theory.Comment: 16 pages, 10 figure
Quantum mechanical path integrals and thermal radiation in static curved spacetimes
The propagator of a spinless particle is calculated from the quantum
mechanical path integral formalism in static curved spacetimes endowed with
event-horizons. A toy model, the Gui spacetime, and the 2D and 4D Schwarzschild
black holes are considered. The role of the topology of the coordinates
configuration space is emphasised in this framework. To cover entirely the
above spacetimes with a single set of coordinates, tortoise coordinates are
extended to complex values. It is shown that the homotopic properties of the
complex tortoise configuration space imply the thermal behaviour of the
propagator in these spacetimes. The propagator is calculated when end points
are located in identical or distinct spacetime regions separated by one or
several event-horizons. Quantum evolution through the event-horizons is shown
to be unitary in the fifth variable.Comment: 22 pages, 10 figure
Global Anomalies in the Batalin Vilkovisky Quantization
The Batalin Vilkovisky (BV) quantization provides a general procedure for
calculating anomalies associated to gauge symmetries. Recent results show that
even higher loop order contributions can be calculated by introducing an
appropriate regularization-renormalization scheme. However, in its standard
form, the BV quantization is not sensible to quantum violations of the
classical conservation of Noether currents, the so called global anomalies. We
show here that the BV field antifield method can be extended in such a way that
the Ward identities involving divergencies of global Abelian currents can be
calculated from the generating functional, a result that would not be obtained
by just associating constant ghosts to global symmetries. This extension,
consisting of trivially gauging the global Abelian symmetries, poses no extra
obstruction to the solution of the master equation, as it happens in the case
of gauge anomalies. We illustrate the procedure with the axial model and also
calculating the Adler Bell Jackiw anomaly.Comment: We emphasized the fact that our procedure only works for the case of
Abelian global anomalies. Section 3 was rewritten and some references were
added. 12 pages, LATEX. Revised version that will appear in Phys. Rev.
Stereotactic ablative body radiotherapy combined with immunotherapy: Present status and future perspectives
Radiotherapy is along with surgery and chemotherapy one of the prime treatment modalities in cancer. It is applied in the primary, neoadjuvant as well as the adjuvant setting. Radiation techniques have rapidly evolved during the past decade enabling the delivery of high radiation doses, reducing side-effects in tumour-adjacent normal tissues. While increasing local tumour control, current and future efforts ought to deal with microscopic disease at a distance of the primary tumour, ultimately responsible for disease-progression. This review explores the possibility of bimodal treatment combining radiotherapy with immunotherapy
The conformal current algebra on supergroups with applications to the spectrum and integrability
We compute the algebra of left and right currents for a principal chiral
model with arbitrary Wess-Zumino term on supergroups with zero Killing form. We
define primary fields for the current algebra that match the affine primaries
at the Wess-Zumino-Witten points. The Maurer-Cartan equation together with
current conservation tightly constrain the current-current and current-primary
operator product expansions. The Hilbert space of the theory is generated by
acting with the currents on primary fields. We compute the conformal dimensions
of a subset of these states in the large radius limit. The current algebra is
shown to be consistent with the quantum integrability of these models to
several orders in perturbation theory.Comment: 45 pages. Minor correction
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