37 research outputs found
DeWitt-Virasoro construction
We study a particular approach for analyzing worldsheet conformal invariance
for bosonic string propagating in a curved background using hamiltonian
formalism. We work in the Schrodinger picture of a single particle description
of the problem where the particle moves in an infinite-dimensional space.
Background independence is maintained in this approach by adopting DeWitt's
(Phys.Rev.85:653-661,1952) coordinate independent formulation of quantum
mechanics. This enables us to construct certain background independent notion
of Virasoro generators, called DeWitt-Virasoro (DWV) generators, and invariant
matrix elements of an arbitrary operator constructed out of them in spin-zero
representation. We show that the DWV algebra is given by the Witt algebra with
additional anomalous terms that vanish for Ricci-flat backgrounds. The actual
quantum Virasoro generators should be obtained by first introducing the vacuum
state and then normal ordering the DWV generators with respect to that. We
demonstrate the procedure in the simple cases of flat and pp-wave backgrounds.
This is a shorter version of arXiv:0912.3987 [hep-th] with many technical
derivations omitted.Comment: 18 pages, shorter version of arXiv:0912.3987 [hep-th] accepted for
publication in Pramana - Journal of Physic
On a coordinate independent description of string worldsheet theory
We study worldsheet conformal invariance for bosonic string propagating in a
curved background using the hamiltonian formalism. In order to formulate the
problem in a background independent manner we first rewrite the worldsheet
theory in a language where it describes a single particle moving in an
infinite-dimensional curved spacetime. This language is developed at a formal
level without regularizing the infinite-dimensional traces. Then we adopt
DeWitt's (Phys.Rev.85:653-661,1952) coordinate independent formulation of
quantum mechanics in the present context. Given the expressions for the
classical Virasoro generators, this procedure enables us to define the
coordinate invariant quantum analogues which we call DeWitt-Virasoro
generators. This framework also enables us to calculate the invariant matrix
elements of an arbitrary operator constructed out of the DeWitt-Virasoro
generators between two arbitrary scalar states. Using these tools we further
calculate the DeWitt-Virasoro algebra in spin-zero representation. The result
is given by the Witt algebra with additional anomalous terms that vanish for
Ricci-flat backgrounds. Further analysis need to be performed in order to
precisely relate this with the beta function computation of Friedan and others.
Finally, we explain how this analysis improves the understanding of showing
conformal invariance for certain pp-wave that has been recently discussed using
hamiltonian framework.Comment: 32 pages, some reorganization for more elaborate explanation, no
change in conclusio
Direct photons in d+Au collisions at s_(NN)**(1/2)=200GeV with STAR
Results are presented of an ongoing analysis of direct photon production in
s_(NN)=200GeV deuteron-gold collisions with the STAR experiment at RHIC. A
significant excess of direct photons is observed near mid-rapidity 0<y<1 and
found to be consistent with next-to-leading order pQCD calculations including
the contribution from fragmentation photons.Comment: 4 pages, 4 figures, HotQuarks 200
Measurement of direct photon production at Tevatron fixed target energies
Measurements of the production of high transverse momentum direct photons by
a 515 GeV/c piminus beam and 530 and 800 GeV/c proton beams in interactions
with beryllium and hydrogen targets are presented. The data span the kinematic
ranges of 3.5 < p_T < 12 GeV/c in transverse momentum and 1.5 units in
rapidity. The inclusive direct-photon cross sections are compared with
next-to-leading-order perturbative QCD calculations and expectations based on a
phenomenological parton-k_T model.Comment: RevTeX4, 23 pages, 32 figures, submitted to Phys. Rev.
1-loop Korrekturen fuer N=1 Supergravitationsmodelle
SIGLEAvailable from the library of Heidelberg Univ. (DE) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman