235 research outputs found
Domain Growth and Finite-Size-Scaling in the Kinetic Ising Model
This paper describes the application of finite-size scaling concepts to
domain growth in systems with a non-conserved order parameter. A finite-size
scaling ansatz for the time-dependent order parameter distribution function is
proposed, and tested with extensive Monte-Carlo simulations of domain growth in
the 2-D spin-flip kinetic Ising model. The scaling properties of the
distribution functions serve to elucidate the configurational self-similarity
that underlies the dynamic scaling picture. Moreover, it is demonstrated that
the application of finite-size-scaling techniques facilitates the accurate
determination of the bulk growth exponent even in the presence of strong
finite-size effects, the scale and character of which are graphically exposed
by the order parameter distribution function. In addition it is found that one
commonly used measure of domain size--the scaled second moment of the
magnetisation distribution--belies the full extent of these finite-size
effects.Comment: 13 pages, Latex. Figures available on request. Rep #9401
The Puzzle of the Flyby Anomaly
Close planetary flybys are frequently employed as a technique to place
spacecraft on extreme solar system trajectories that would otherwise require
much larger booster vehicles or may not even be feasible when relying solely on
chemical propulsion. The theoretical description of the flybys, referred to as
gravity assists, is well established. However, there seems to be a lack of
understanding of the physical processes occurring during these dynamical
events. Radio-metric tracking data received from a number of spacecraft that
experienced an Earth gravity assist indicate the presence of an unexpected
energy change that happened during the flyby and cannot be explained by the
standard methods of modern astrodynamics. This puzzling behavior of several
spacecraft has become known as the flyby anomaly. We present the summary of the
recent anomalous observations and discuss possible ways to resolve this puzzle.Comment: 6 pages, 1 figure. Accepted for publication by Space Science Review
Comparative study of loop contributions in AdS and dS
The generic feature of non-conformal fields in Poincare patch of de Sitter
space is the presence of large IR loop corrections even for massive fields.
Moreover, in global de Sitter there are loop IR divergences for the massive
fields. Naive analytic continuation from de Sitter to Anti-de-Sitter might lead
one to conclude that something similar should happen in the latter space as
well. However, we show that there are no large IR effects in the one-loop
two-point functions in the Poincare patch of Anti-de-Sitter space even for the
zero mass minimally coupled scalar fields. As well there are neither large IR
effects nor IR divergences in global Anti-de-Sitter space even for the zero
mass.Comment: 12 pages. Minor changes, misprints are correcte
The large-scale energetic ion layer in the high latitude Jovian magnetosphere as revealed by Ulysses/HI-SCALE cross-field intensity-gradient measurements
Ulysses investigated the high latitude Jovian magnetosphere for a second time
after Pioneer 11 mission and gave us the opportunity to search the structure
and the dynamics of this giant magnetosphere above the magnetodisc.
Kivelson(1976) and Kennel & Coroniti(1979) reported that Pioneer 11 observed
energetic particle intensities at high latitudes at the same level with those
measured in the plasma sheet and inferred that they were not consistent with
the magnetodisc model. Ulysses observations supported the idea about a
large-scale layer of energetic ions and electrons in the outer high latitude
Jovian magnetosphere (Cowley et al.1996; Anagnostopoulos et al. 2001). This
study perform a number of further tests for the existence of the large scale
layer of energetic ions in the outer high latitude Jovian magnetosphere by
studying appropriate cross-B field anisotropies in order to monitor the ion
northward/southward intensity gradients. In particular, we examined
Ulysses/HI-SCALE observations of energetic ions with large gyro-radius
(0.5-1.6MeV protons and >2.5MeV heavy(Z>5) ions) in order to compare instant
intensity changes with remote sensing intensity gradients. Our analysis
confirms the existence of an energetic particle layer in the north hemisphere,
during the inbound trajectory of Ulysses traveling at moderate latitudes, and
in the south high-latitude duskside magnetosphere, during the outbound segment
of the spacecraft trajectory. Our Ulysses/HI-SCALE data analysis also provides
evidence for the detection of an energetic proton magnetopause boundary layer
during the outbound trajectory of the spacecraft. During Ulysses flyby of
Jupiter the almost permanent appearance of alternative northward and southward
intensity gradients suggests that the high latitude layer appeared to be a
third major area of energetic particles, which coexisted with the radiation
belts and the magnetodisc.Comment: 37 pages, 11 figures, 1 tabl
Semiclassical Quantization of Effective String Theory and Regge Trajectories
We begin with an effective string theory for long distance QCD, and evaluate
the semiclassical expansion of this theory about a classical rotating string
solution, taking into account the the dynamics of the boundary of the string.
We show that, after renormalization, the zero point energy of the string
fluctuations remains finite when the masses of the quarks on the ends of the
string approach zero. The theory is then conformally invariant in any spacetime
dimension D. For D=26 the energy spectrum of the rotating string formally
coincides with that of the open string in classical Bosonic string theory.
However, its physical origin is different. It is a semiclassical spectrum of an
effective string theory valid only for large values of the angular momentum.
For D=4, the first semiclassical correction adds the constant 1/12 to the
classical Regge formula.Comment: 65 pages, revtex, 3 figures, added 2 reference
de Sitter spacetime: effects of metric perturbations on geodesic motion
Gravitational perturbations of the de Sitter spacetime are investigated using
the Regge--Wheeler formalism. The set of perturbation equations is reduced to a
single second order differential equation of the Heun-type for both electric
and magnetic multipoles. The solution so obtained is used to study the
deviation from an initially radial geodesic due to the perturbation. The
spectral properties of the perturbed metric are also analyzed. Finally, gauge-
and tetrad-invariant first-order massless perturbations of any spin are
explored following the approach of Teukolsky. The existence of closed-form,
i.e. Liouvillian, solutions to the radial part of the Teukolsky master equation
is discussed.Comment: IOP macros, 10 figure
The one-loop vacuum energy and RG flow induced by double-trace operators in AdS/CFT and dS/CFT correspondence
We calculate the difference of one-loop vacuum energies for massive scalar
field in five-dimensional AdS black hole. (The same is done in five-dimensional
deSitter space). In each case this difference is specified by the boundary
conditions corresponding to the double-trace operator (massive term) and it
describes RG flow in the manner discussed by Gubser-Mitra for pure AdS space.
For AdS black hole there occurs instability which is the manifestation of the
Hawking-Page phase transition. For stable phase of AdS black hole as well as
for deSitter bulk, c-function found beyond the leading order approximation
shows the monotonic behaviour consistent with c-theorem.Comment: LaTeX file, 3 eps files, 26 pages. The discussion is clarified,
version to appear in PR
Lagrangian evolution of global strings
We establish a method to trace the Lagrangian evolution of extended objects
consisting of a multicomponent scalar field in terms of a numerical calculation
of field equations in three dimensional Eulerian meshes. We apply our method to
the cosmological evolution of global strings and evaluate the energy density,
peculiar velocity, Lorentz factor, formation rate of loops, and emission rate
of Nambu-Goldstone (NG) bosons. We confirm the scaling behavior with a number
of long strings per horizon volume smaller than the case of local strings by a
factor of 10. The strategy and the method established here are
applicable to a variety of fields in physics.Comment: 5 pages, 2 figure
Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection
Realistic astrophysical environments are turbulent due to the extremely high
Reynolds numbers. Therefore, the theories of reconnection intended for
describing astrophysical reconnection should not ignore the effects of
turbulence on magnetic reconnection. Turbulence is known to change the nature
of many physical processes dramatically and in this review we claim that
magnetic reconnection is not an exception. We stress that not only
astrophysical turbulence is ubiquitous, but also magnetic reconnection itself
induces turbulence. Thus turbulence must be accounted for in any realistic
astrophysical reconnection setup. We argue that due to the similarities of MHD
turbulence in relativistic and non-relativistic cases the theory of magnetic
reconnection developed for the non-relativistic case can be extended to the
relativistic case and we provide numerical simulations that support this
conjecture. We also provide quantitative comparisons of the theoretical
predictions and results of numerical experiments, including the situations when
turbulent reconnection is self-driven, i.e. the turbulence in the system is
generated by the reconnection process itself. We show how turbulent
reconnection entails the violation of magnetic flux freezing, the conclusion
that has really far reaching consequences for many realistically turbulent
astrophysical environments. In addition, we consider observational testing of
turbulent reconnection as well as numerous implications of the theory. The
former includes the Sun and solar wind reconnection, while the latter include
the process of reconnection diffusion induced by turbulent reconnection, the
acceleration of energetic particles, bursts of turbulent reconnection related
to black hole sources as well as gamma ray bursts. Finally, we explain why
turbulent reconnection cannot be explained by turbulent resistivity or derived
through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection -
Concepts and Applications", editors W. Gonzalez, E. N. Parke
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