49 research outputs found
Data management study, volume 5. Appendix A - Contractor data package technical description and system engineering /SE/ Final report
Technical description and systems engineering contractor data package for Voyager spacecraf
Exact renormalization group equations and the field theoretical approach to critical phenomena
After a brief presentation of the exact renormalization group equation, we
illustrate how the field theoretical (perturbative) approach to critical
phenomena takes place in the more general Wilson (nonperturbative) approach.
Notions such as the continuum limit and the renormalizability and the presence
of singularities in the perturbative series are discussed.Comment: 15 pages, 7 figures, to appear in the Proceedings of the 2nd
Conference on the Exact Renormalization Group, Rome 200
Random matrix analysis of the QCD sign problem for general topology
Motivated by the important role played by the phase of the fermion
determinant in the investigation of the sign problem in lattice QCD at nonzero
baryon density, we derive an analytical formula for the average phase factor of
the fermion determinant for general topology in the microscopic limit of chiral
random matrix theory at nonzero chemical potential, for both the quenched and
the unquenched case. The formula is a nontrivial extension of the expression
for zero topology derived earlier by Splittorff and Verbaarschot. Our
analytical predictions are verified by detailed numerical random matrix
simulations of the quenched theory.Comment: 33 pages, 9 figures; v2: minor corrections, references added, figures
with increased statistics, as published in JHE
The Regge Limit for Green Functions in Conformal Field Theory
We define a Regge limit for off-shell Green functions in quantum field
theory, and study it in the particular case of conformal field theories (CFT).
Our limit differs from that defined in arXiv:0801.3002, the latter being only a
particular corner of the Regge regime. By studying the limit for free CFTs, we
are able to reproduce the Low-Nussinov, BFKL approach to the pomeron at weak
coupling. The dominance of Feynman graphs where only two high momentum lines
are exchanged in the t-channel, follows simply from the free field analysis. We
can then define the BFKL kernel in terms of the two point function of a simple
light-like bilocal operator. We also include a brief discussion of the gravity
dual predictions for the Regge limit at strong coupling.Comment: 23 pages 2 figures, v2: Clarification of relation of the Regge limit
defined here and previous work in CFT. Clarification of causal orderings in
the limit. References adde
Once again on the equivalence theorem
We present the proof of the equivalence theorem in quantum field theory which
is based on a formulation of this problem in the field-antifield formalism. As
an example, we consider a model in which a different choices of natural finite
counterterms is possible, leading to physically non-equivalent quantum theories
while the equivalent theorem remains valid.Comment: 12 pages, LATEX, report number was correcte
Large Representation Recurrences in Large N Random Unitary Matrix Models
In a random unitary matrix model at large N, we study the properties of the
expectation value of the character of the unitary matrix in the rank k
symmetric tensor representation. We address the problem of whether the standard
semiclassical technique for solving the model in the large N limit can be
applied when the representation is very large, with k of order N. We find that
the eigenvalues do indeed localize on an extremum of the effective potential;
however, for finite but sufficiently large k/N, it is not possible to replace
the discrete eigenvalue density with a continuous one. Nonetheless, the
expectation value of the character has a well-defined large N limit, and when
the discreteness of the eigenvalues is properly accounted for, it shows an
intriguing approximate periodicity as a function of k/N.Comment: 24 pages, 11 figure
The conformal frame freedom in theories of gravitation
It has frequently been claimed in the literature that the classical physical
predictions of scalar tensor theories of gravity depend on the conformal frame
in which the theory is formulated. We argue that this claim is false, and that
all classical physical predictions are conformal-frame invariants. We also
respond to criticisms by Vollick [gr-qc/0312041], in which this issue arises,
of our recent analysis of the Palatini form of 1/R gravity.Comment: 9 pages, no figures, revtex; final published versio
Elastic and Raman scattering of 9.0 and 11.4 MeV photons from Au, Dy and In
Monoenergetic photons between 8.8 and 11.4 MeV were scattered elastically and
in elastically (Raman) from natural targets of Au, Dy and In.15 new cross
sections were measured. Evidence is presented for a slight deformation in the
197Au nucleus, generally believed to be spherical. It is predicted, on the
basis of these measurements, that the Giant Dipole Resonance of Dy is very
similar to that of 160Gd. A narrow isolated resonance at 9.0 MeV is observed in
In.Comment: 31 pages, 11 figure
High orders of perturbation theory: are renormalons significant?
According to Lipatov, the high orders of perturbation theory are determined
by saddle-point configurations (instantons) of the corresponding functional
integrals. According to t'Hooft, some individual large diagrams, renormalons,
are also significant and they are not contained in the Lipatov contribution.
The history of the conception of renormalons is presented, and the arguments in
favor of and against their significance are discussed. The analytic properties
of the Borel transforms of functional integrals, Green functions, vertex parts,
and scaling functions are investigated in the case of \phi^4 theory. Their
analyticity in a complex plane with a cut from the first instanton singularity
to infinity (the Le Guillou - Zinn-Justin hypothesis) is proved. It rules out
the existence of the renormalon singularities pointed out by t'Hooft and
demonstrates the nonconstructiveness of the conception of renormalons as a
whole. The results can be interpreted as an indication of the internal
consistency of \phi^4 theory.Comment: 28 pages, 8 figures include
Functional Renormalization Group and the Field Theory of Disordered Elastic Systems
We study elastic systems such as interfaces or lattices, pinned by quenched
disorder. To escape triviality as a result of ``dimensional reduction'', we use
the functional renormalization group. Difficulties arise in the calculation of
the renormalization group functions beyond 1-loop order. Even worse,
observables such as the 2-point correlation function exhibit the same problem
already at 1-loop order. These difficulties are due to the non-analyticity of
the renormalized disorder correlator at zero temperature, which is inherent to
the physics beyond the Larkin length, characterized by many metastable states.
As a result, 2-loop diagrams, which involve derivatives of the disorder
correlator at the non-analytic point, are naively "ambiguous''. We examine
several routes out of this dilemma, which lead to a unique renormalizable
field-theory at 2-loop order. It is also the only theory consistent with the
potentiality of the problem. The beta-function differs from previous work and
the one at depinning by novel "anomalous terms''. For interfaces and random
bond disorder we find a roughness exponent zeta = 0.20829804 epsilon + 0.006858
epsilon^2, epsilon = 4-d. For random field disorder we find zeta = epsilon/3
and compute universal amplitudes to order epsilon^2. For periodic systems we
evaluate the universal amplitude of the 2-point function. We also clarify the
dependence of universal amplitudes on the boundary conditions at large scale.
All predictions are in good agreement with numerical and exact results, and an
improvement over one loop. Finally we calculate higher correlation functions,
which turn out to be equivalent to those at depinning to leading order in
epsilon.Comment: 42 pages, 41 figure