2,670 research outputs found
Stochastic model of optical variability of BL Lacertae
We use optical photometric and polarimetric data of BL Lacertae that cover a
period of 22 years to study the variability of the source. The long-term
observations are employed for establishing parameters of a stochastic model
consisting of the radiation from a steady polarized source and a number of
variable components with different polarization parameters, proposed by
Hagen-Thorn et al. earlier. We infer parameters of the model from the
observations using numerical simulations based on a Monte Carlo method, with
values of each model parameter selected from a Gaussian distribution. We
determine the best set of model parameters by comparing model distributions to
the observational ones using the chi-square criterion. We show that the
observed photometric and polarimetric variability can be explained within a
model with a steady source of high polarization, ~40%, and with direction of
polarization parallel to the parsec scale jet, along with 10+-5 sources of
variable polarization.Comment: 4 pages, 10 figures, published by Astronomy and Astrophysics; v2:
typos correcte
Bag Model for a Link in a Closed Gluonic Chain
The large limit of Yang-Mills gauge theory is the dynamics of a closed
gluonic chain, but this fact does not obviate the inherently strong coupling
nature of the dynamical problem. However, we suggest that a single link in such
a chain might be reasonably described in the quasi-perturbative language of
gluons and their interactions. To implement this idea, we use the MIT bag to
model the physics of a nearest neighbor bond.Comment: 10 pages, LaTe
Calculating the Rest Tension for a Polymer of String Bits
We explore the application of approximation schemes from many body physics,
including the Hartree-Fock method and random phase approximation (RPA), to the
problem of analyzing the low energy excitations of a polymer chain made up of
bosonic string bits. We accordingly obtain an expression for the rest tension
of the bosonic relativistic string in terms of the parameters
characterizing the microscopic string bit dynamics. We first derive an exact
connection between the string tension and a certain correlation function of the
many-body string bit system. This connection is made for an arbitrary
interaction potential between string bits and relies on an exact dipole sum
rule. We then review an earlier calculation by Goldstone of the low energy
excitations of a polymer chain using RPA. We assess the accuracy of the RPA by
calculating the first order corrections. For this purpose we specialize to the
unique scale invariant potential, namely an attractive delta function potential
in two (transverse) dimensions. We find that the corrections are large, and
discuss a method for summing the large terms. The corrections to this improved
RPA are roughly 15\%.Comment: 44 pages, phyzzx, psfig required, Univ. of Florida preprint,
UFIFT-HEP-94
More On The Connection Between Planar Field Theory And String Theory
We continue work on the connection between world sheet representation of the
planar phi^3 theory and string formation. The present article, like the earlier
work, is based on the existence of a solitonic solution on the world sheet, and
on the zero mode fluctuations around this solution. The main advance made in
this paper is the removal of the cutoff and the transition to the continuum
limit on the world sheet. The result is an action for the modes whose energies
remain finite in this limit (light modes). The expansion of this action about a
dense background of graphs on the world sheet leads to the formation of a
string.Comment: 27 pages, 3 figure
-Dimensional Large QCD coupled to Adjoint Fermions
We consider 1+1-dimensional QCD coupled to Majorana fermions in the adjoint
representation of the gauge group . Pair creation of partons (fermion
quanta) is not suppressed in the large- limit, where the glueball-like bound
states become free. In this limit the spectrum is given by a linear \lc\ Schr\"
odinger equation, which we study numerically using the discretized \lcq. We
find a discrete spectrum of bound states, with the logarithm of the level
density growing approximately linearly with the mass. The wave function of a
typical excited state is a complicated mixture of components with different
parton numbers. A few low-lying states, however, are surprisingly close to
being eigenstates of the parton number, and their masses can be accurately
calculated by truncated diagonalizations.Comment: 22 pages + 9 figures (available by request from
[email protected]), uses phyzzx.tex + tables.tex PUPT-1413,
IASSNS-HEP-93/4
Field Theory On The World Sheet: Improvements And Generalizations
This article is the continuation of a project of investigating planar phi^3
model in various dimensions. The idea is to reformulate them on the world
sheet, and then to apply the classical (meanfield) approximation, with two
goals: To show that the ground state of the model is a solitonic configuration
on the world sheet, and the quantum fluctuations around the soliton lead to the
formation of a transverse string. After a review of some of the earlier work,
we introduce and discuss several generalizations and new results. In 1+2
dimensions, a rigorous upper bound on the solitonic energy is established. A
phi^4 interaction is added to stabilize the original phi^3 model. In 1+3 and
1+5 dimensions, an improved treatment of the ultraviolet divergences is given.
And significantly, we show that our approximation scheme can be imbedded into a
systematic strong coupling expansion. Finally, the spectrum of quantum
fluctuations around the soliton confirms earlier results: In 1+2 and 1+3
dimensions, a transverse string is formed on the world sheet.Comment: 29 pages, 5 figures, several typos and eqs.(74) and (75) are
corrected, a comment added to section
Spontaneous Symmetry Breaking at Infinite Momentum without P+ Zero-Modes
The nonrelativistic interpretation of quantum field theory achieved by
quantization in an infinite momentum frame is spoiled by the inclusion of a
mode of the field carrying p+=0. We therefore explore the viability of doing
without such a mode in the context of spontaneous symmetry breaking (SSB),
where its presence would seem to be most needed. We show that the physics of
SSB in scalar quantum field theory in 1+1 space-time dimensions is accurately
described without a zero-mode.Comment: LaTeX, 8 pages, 3 eps figure
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