86 research outputs found
Multipole moments in Kaluza-Klein theories
This paper contains discussion of the problem of motion of extended i.e. non
point test bodies in multidimensional space. Extended bodies are described in
terms of so called multipole moments. Using approximated form of equations of
motion for extended bodies deviation from geodesic motion is derived. Results
are applied to special form of space-time.Comment: 11 pages, AMS-TeX, few misprints corrected, to appear in Classical
and Quantum Gravit
Schwinger-Dyson equation for non-Lagrangian field theory
A method is proposed of constructing quantum correlators for a general gauge
system whose classical equations of motion do not necessarily follow from the
least action principle. The idea of the method is in assigning a certain BRST
operator to any classical equations of motion, Lagrangian or not.
The generating functional of Green's functions is defined by the equation
that is reduced to the standard Schwinger-Dyson equation
whenever the classical field equations are Lagrangian. The corresponding
probability amplitude of a field is defined by the same equation
although in another representation. When the
classical dynamics are Lagrangian, the solution for is reduced to
the Feynman amplitude , while in the non-Lagrangian case
this amplitude can be a more general distribution.Comment: 33 page
Kinetic equation for gluons at the early stage
We derive the kinetic equation for pure gluon QCD plasma in a general way,
applying the background field method. We show that the quantum kinetic equation
contains a term as in the classical case, that describes a color charge
precession of partons moving in the gauge field. We emphasize that this new
term is necessary for the gauge covariance of the resulting equation.Comment: 6 pages, no figure, to appear in the proceedings of the 6th
international conference on strange quarks in matter, Frankfurt, Germany,
25-29 september 200
Kinetic Equation for Gluons in the Background Gauge of QCD
We derive the quantum kinetic equation for a pure gluon plasma, applying the
background field and closed-time-path method. The derivation is more general
and transparent than earlier works. A term in the equation is found which, as
in the classical case, corresponds to the color charge precession for partons
moving in the gauge field.Comment: RevTex 4, 4 pages, no figure, PRL accepted versio
The role of Background Independence for Asymptotic Safety in Quantum Einstein Gravity
We discuss various basic conceptual issues related to coarse graining flows
in quantum gravity. In particular the requirement of background independence is
shown to lead to renormalization group (RG) flows which are significantly
different from their analogs on a rigid background spacetime. The importance of
these findings for the asymptotic safety approach to Quantum Einstein Gravity
(QEG) is demonstrated in a simplified setting where only the conformal factor
is quantized. We identify background independence as a (the ?) key prerequisite
for the existence of a non-Gaussian RG fixed point and the renormalizability of
QEG.Comment: 2 figures. Talk given by M.R. at the WE-Heraeus-Seminar "Quantum
Gravity: Challenges and Perspectives", Bad Honnef, April 14-16, 2008; to
appear in General Relativity and Gravitatio
Dirac's Observables for the Rest-Frame Instant Form of Tetrad Gravity in a Completely Fixed 3-Orthogonal Gauge
We define the {\it rest-frame instant form} of tetrad gravity restricted to
Christodoulou-Klainermann spacetimes. After a study of the Hamiltonian group of
gauge transformations generated by the 14 first class constraints of the
theory, we define and solve the multitemporal equations associated with the
rotation and space diffeomorphism constraints, finding how the cotriads and
their momenta depend on the corresponding gauge variables. This allows to find
quasi-Shanmugadhasan canonical transformation to the class of 3-orthogonal
gauges and to find the Dirac observables for superspace in these gauges.
The construction of the explicit form of the transformation and of the
solution of the rotation and supermomentum constraints is reduced to solve a
system of elliptic linear and quasi-linear partial differential equations. We
then show that the superhamiltonian constraint becomes the Lichnerowicz
equation for the conformal factor of the 3-metric and that the last gauge
variable is the momentum conjugated to the conformal factor. The gauge
transformations generated by the superhamiltonian constraint perform the
transitions among the allowed foliations of spacetime, so that the theory is
independent from its 3+1 splittings. In the special 3-orthogonal gauge defined
by the vanishing of the conformal factor momentum we determine the final Dirac
observables for the gravitational field even if we are not able to solve the
Lichnerowicz equation. The final Hamiltonian is the weak ADM energy restricted
to this completely fixed gauge.Comment: RevTeX file, 141 page
Morphological Variation Among Wild Populations of Chinese Rare Minnow ( Gobiocypris rarus
The Thermal Beta-Function in Yang-Mills Theory
Previous calculations of the thermal beta-function in a hot Yang--Mills gas
at the one--loop level have exposed problems with the gauge dependence and with
the sign, which is opposite to what one would expect for asymptotic freedom. We
show that inclusion of higher--loop effects through a static Braaten--Pisarski
resummation is necessary to consistently obtain the leading term, but alters
the results only quantitatively. The sign, in particular, remains the same. We
also explore, by a crude parameterization, the effects a (non--perturbative)
magnetic mass may have on these results.Comment: 16pp,latex + epsf.sty, Nordita-94/36
The effects of stimulus complexity on the preattentive processing of self-generated and nonself voices: an ERP study
The ability to differentiate one's own voice from the voice of somebody else plays a critical role in successful verbal self-monitoring processes and in communication. However, most of the existing studies have only focused on the sensory correlates of self-generated voice processing, whereas the effects of attentional demands and stimulus complexity on self-generated voice processing remain largely unknown. In this study, we investigated the effects of stimulus complexity on the preattentive processing of self and nonself voice stimuli. Event-related potentials (ERPs) were recorded from 17 healthy males who watched a silent movie while ignoring prerecorded self-generated (SGV) and nonself (NSV) voice stimuli, consisting of a vocalization (vocalization category condition: VCC) or of a disyllabic word (word category condition: WCC). All voice stimuli were presented as standard and deviant events in four distinct oddball sequences. The mismatch negativity (MMN) ERP component peaked earlier for NSV than for SGV stimuli. Moreover, when compared with SGV stimuli, the P3a amplitude was increased for NSV stimuli in the VCC only, whereas in the WCC no significant differences were found between the two voice types. These findings suggest differences in the time course of automatic detection of a change in voice identity. In addition, they suggest that stimulus complexity modulates the magnitude of the orienting response to SGV and NSV stimuli, extending previous findings on self-voice processing.This work was supported by Grant Numbers IF/00334/2012, PTDC/PSI-PCL/116626/2010, and PTDC/MHN-PCN/3606/2012, funded by the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal) and the Fundo Europeu de Desenvolvimento Regional through the European programs Quadro de Referencia Estrategico Nacional and Programa Operacional Factores de Competitividade, awarded to A.P.P., and by FCT Doctoral Grant Number SFRH/BD/77681/2011, awarded to T.C.info:eu-repo/semantics/publishedVersio
Some Results on Cubic and Higher Order Extensions of the Poincar\'e Algebra
In these lectures we study some possible higher order (of degree greater than
two) extensions of the Poincar\'e algebra. We first give some general
properties of Lie superalgebras with some emphasis on the supersymmetric
extension of the Poincar\'e algebra or Supersymmetry. Some general features on
the so-called Wess-Zumino model (the simplest field theory invariant under
Supersymmetry) are then given. We further introduce an additional algebraic
structure called Lie algebras of order F, which naturally comprise the concepts
of ordinary Lie algebras and superalgebras. This structure enables us to define
various non-trivial extensions of the Poincar\'e algebra. These extensions are
studied more precisely in two different contexts. The first algebra we are
considering is shown to be an (infinite dimensional) higher order extension of
the Poincar\'e algebra in dimensions and turns out to induce a symmetry
which connects relativistic anyons. The second extension we are studying is
related to a specific finite dimensional Lie algebra of order three, which is a
cubic extension of the Poincar\'e algebra in space-time dimensions.
Invariant Lagrangians are constructed.Comment: Mini course given at the Workshop higher symmetries in physics,
Madrid, Spain, November 6-8, 200
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