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Small scale structure on cosmic strings

Description: I discuss our current understanding of cosmic string evolution, and focus on the question of small scale structure on strings, where most of the disagreements lie. I present a physical picture designed to put the role of the small scale structure into more intuitive terms. In this picture one can see how the small scale structure can feed back in a major way on the overall scaling solution. I also argue that it is easy for small scale numerical errors to feed back in just such a way. The intuitive discussion presented here may form the basis for an analytic treatment of the small structure, which I argue in any case would be extremely valuable in filling the gaps in our resent understanding of cosmic string evolution. 24 refs., 8 figs.
Date: October 30, 1989
Creator: Albrecht, A.
Partner: UNT Libraries Government Documents Department

Evolution of cosmic string networks

Description: We summarize our new results on cosmic strings. These results include: the application of non-equilibrium statistical mechanics to cosmic string evolution, a simple ''one scale'' model for the long strings which has a great deal of predictive power, results from large scale numerical simulations, and a discussion of the observational consequences of our results. An upper bond on G/mu/ of approximately 10/sup /minus/7/ emerges from the millisecond pulsar gravity wave bound. We discuss how numerical uncertainties affect this. Any changes which weaken the bound would probably also give the long strings the dominant role in producing observational consequences. 22 refs.
Date: June 1, 1989
Creator: Albrecht, A. & Turok, N.
Partner: UNT Libraries Government Documents Department

Phenomenological implications of the blown-up orbifolds

Description: We discuss the structure of the effective Lagrangian for the (2,2) Z/sub N/ orbifolds and the corresponding Calabi-Yau manifolds which are obtained by ''blowing-up'' the orbifold singularities. The method to ''blow-up'' such singularities is reviewed. Results are exact at the string tree-level. In particular, the question of generating an intermediate scale M/sub I/ in such models is addressed. It is shown that for Z/sub N/ orbifolds (except one) and the corresponding blown-up orbifolds which are compactified on any six-torus T/sup 6/ which can be obtained by continuously deforming T/sup 4/ circle times T/sup 2/, all the terms of the type (2727)/sup K/ are absent from the effective superpotential, thus questioning the mechanism for generating a large intermediate scale for such compactifications.
Date: May 1, 1987
Creator: Cvetic, M.
Partner: UNT Libraries Government Documents Department

Bordered surfaces, off-shell amplitudes, sewing, and string field theory

Description: These lectures will deal with the current status of the sewing problem. The rationale for this approach is that any nonperturbative string theory must reproduce the Polyakov path integral as a perturbation series. If our experience in ordinary field theory is a guide --- and admittedly it may not be --- the terms in such a perturbation series, like Feynman diagrams, are likely to be built up from simple ''vertices'' and ''propagators,'' which can themselves be represented as (off-shell) Polyakov amplitudes. Hence an understanding of how to put together simple components into more complicated world sheet amplitudes is likely to give us much-needed information about the structure of nonperturbative string theory. To understand sewing, we must first understand the building blocks, off-shell Polyakov amplitudes. This is the subject of my first lecture. Next, we will explore the sewing of conformal field theories at a fixed conformal structure, that is, the reconstruction of correlation functions for a fixed surface /Sigma/ from those on a pair of surfaces /Sigma//sub 1/ and /Sigma//sub 2/ obtained by cutting /Sigma/ along a closed curve. We will then look at the problem of sewing amplitudes, integrals of correlation functions over moduli space. This will necessitate an understanding of how to build the moduli space of a complicated surface from simpler moduli spaces. Finally, we will briefly examine vertices and string field theories. 48 refs., 10 figs.
Date: April 1, 1989
Creator: Carlip, S.
Partner: UNT Libraries Government Documents Department

Two loop partition function in (compactified) heterotic string vacua

Description: Two loop partition function for the heterotic string theory, compactified on any background preserving space-time supersymmetry at the string tree level, is explicitly calculated. This includes E/sub 8/ x E/sub 8/ or SO(32) heterotic string theory in ten dimensional flat space-time.
Date: October 1, 1987
Creator: Atick, J.J. & Sen, A.
Partner: UNT Libraries Government Documents Department

Gauge invariant actions for string models

Description: String models of unified interactions are elegant sets of Feynman rules for the scattering of gravitons, gauge bosons, and a host of massive excitations. The purpose of these lectures is to describe the progress towards a nonperturbative formulation of the theory. Such a formulation should make the geometrical meaning of string theory manifest and explain the many ''miracles'' exhibited by the string Feynman rules. There are some new results on gauge invariant observables, on the cosmological constant, and on the symmetries of interacting string field theory. 49 refs.
Date: June 1, 1986
Creator: Banks, T.
Partner: UNT Libraries Government Documents Department

Torsion in superstrings

Description: String theories on a background manifold with torsion are discussed. Candidate vacuum configurations are discussed for ten-dimensional superstrings. These are compactified on M/sub 4/ x K, where M/sub 4/ is four-dimensional and K is some compact six-dimensional manifold. Solutions with non-zero torsion on K are emphasized. The compactification problem is approached both from the effective field theory point of view and directly using string considerations. The construction of string theories in curved space with torsion is then discussed. Particular emphasis is put on the constraints on space-time supersymmetry in the Green-Schwarz approach. Two-dimensional non-linear sigma models are used to describe the propagation of strings in background geometries with torsion. (LEW)
Date: September 1, 1985
Creator: Bars, I.; Nemeschansky, D. & Yankielowicz, S.
Partner: UNT Libraries Government Documents Department

Torsion and geometrostasis in covariant superstrings

Description: The covariant action for freely propagating heterotic superstrings consists of a metric and a torsion term with a special relative strength. It is shown that the strength for which torsion flattens the underlying 10-dimensional superspace geometry is precisely that which yields free oscillators on the light cone. This is in complete analogy with the geometrostasis of two-dimensional sigma-models with Wess-Zumino interactions. 13 refs.
Date: January 1, 1985
Creator: Zachos, C.
Partner: UNT Libraries Government Documents Department

Resurrection of neutrinos as dark matter

Description: It is shown that new observations of large scale structure in the universe (voids, foam, and large-scale velocity fields) are best understood if the dominant matter of the universe is in the form of massive (9eV less than or equal to m/sub nu/ less than or equal to 35 eV) neutrinos. Cold dark matter, even with biasing, seems unable to duplicate the combination of these observations (although a fine-tuned loophole with cold matter and percolated explosions may also marginally work.) The previous fatal problems of galaxy formation with neutrinos can be remedied by combining them with either cosmic strings or explosive galaxy formation. The former naturally gives the scale-free correlation function for galaxies, clusters, and superclusters, and gives large, but not necessarily spherical voids. The latter naturally gives spherical voids, but requires fine tuning and percolation to get the large scales and the scale-free correlation function. 39 refs.
Date: May 1, 1986
Creator: Schramm, D.N.
Partner: UNT Libraries Government Documents Department

String driven inflation

Description: It is argued that, in fundamental string theories, as one traces the universe back in time a point is reached when the expansion rate is so fast that the rate of string creation due to quantum effects balances the dilution of the string density due to the expansion. One is therefore led into a phase of constant string density and an exponentially expanding universe. Fundamental strings therefore seem to lead naturally to inflation. 17 refs., 1 fig.
Date: November 1, 1987
Creator: Turok, N.
Partner: UNT Libraries Government Documents Department

Anyons in a magnetic field: Landau levels and vertex operator representation

Description: We construct exact many-body eigenstates of both energy and angular momentum for the N-anyon problem in an external magnetic field. Such states span the full ground-state eigenspace and have a natural representation in terms of the Fubini-Veneziano vertex operators of string theory. 19 refs.
Date: January 1, 1991
Creator: Dunne, G.V.; Lerda, A. (Massachusetts Inst. of Tech., Cambridge, MA (USA)) & Trugenberger, C.A. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Fayet-Iliopoulos D terms in string theory

Description: One loop scalar masses induced by Fayet-Ilipoulos D terms in string theory are calculated directly in the heterotic string theory for an arbitrary compactification which preserves space-time supersymmetry at the string tree level. The result is shown to be a total derivative in the moduli space of a torus with two punctures, and hence receives contribution only from the boundary of this moduli space.
Date: June 1, 1987
Creator: Sen, A.
Partner: UNT Libraries Government Documents Department

String primer

Description: This is an elementary introduction to the classical and quantum mechanics of a single bosonic string, and to some aspects of its supersymmetric and heterotic extensions. 22 refs.
Date: March 1, 1986
Creator: Bachas, C.
Partner: UNT Libraries Government Documents Department

Strings and their compactification from the particle viewpoint

Description: A series of four lectures is given which deals with the particle formulation of string theory. An introductory lecture is given on where the idea of strings comes from and what strings are. An introduction is given to simple Lie algebras and their representations. Compactified strings and the heterotic theories are discussed, showing how infinite-dimensional Kac-Moody affine algebras can be spectrum generating algebras in (open) string theories. The spectrum of excited states of the heterotic string is examined, and comments are made on representations of affine algebras. Some aspects are shown of the algebraic structure of compactified closed bosonic strings. (LEW)
Date: January 1, 1986
Creator: Slansky, R.
Partner: UNT Libraries Government Documents Department

Open superstrings as the theory of everything

Description: We discuss the first examples of one-loop finite four-dimensional superstrings. These examples can be either space-time supersymmetric or not depending on the details of the models. 17 refs.
Date: January 1, 1990
Creator: Bern, Z. (Los Alamos National Lab., NM (USA)) & Dunbar, D.C. (Liverpool Univ. (UK). Dept. of Applied Mathematics and Theoretical Physics)
Partner: UNT Libraries Government Documents Department


Description: The essence of vortex physics is that at certain low-energy scales elementary excitations of a point particle theory can behave like strings rather than particles. Vortices are the resulting string-like solutions; their thickness sets the distance scale beyond which physics is string-like rather than particle-like. String degrees of freedom are massless in the sense that excitations on a string can have an arbitrarily low frequency. Non-string degrees of freedom correspond to massive particles and are absent from the low energy spectrum. This article considers only field theories with vortices at low energies. The possible existence of a class of solitons in these vortex theories will be discussed. They are vortex rings: they are localized and finite in energy, and able to carry the quantum numbers of point particles. Rings are thus particle-like solutions of a vortex theory, which is itself a limit of a point particle field theory.
Date: January 1, 1989
Creator: Davis, R.L.
Partner: UNT Libraries Government Documents Department

Supersymmetry breaking in string theory

Description: I briefly review the problems with previous investigations of supersymmetry breaking in string theory --- at tree-level, at one-loop, and non-perturbatively. A variant of the original non-perturbative scenario is proposed, in which gaugino condensation takes place in two different strongly-interacting hidden-sector gauge groups. In the new scenario it is possible to generate a large hierarchy of mass scale and to simultaneously stabilize the dilaton at a large expectation value (weak coupling). However, it is still uncertain whether supersymmetry is broken in such a vacuum. 26 refs.
Date: April 1, 1990
Creator: Dixon, L.J.
Partner: UNT Libraries Government Documents Department

Computer simulations of the motion and decay of global strings

Description: Computer simulations have been carried out of the motion and decay of global strings, including spectrum analysis of the energy stored in the scalar field which describes the global string and the radiated Nambu-Goldstone bosons. We simulated relaxing pieces of bent string and collapsing loops. We find, for the string sizes investigated, that the spectrum of field energy hardens rather than softens while the string decays into Nambu-Goldstone radiation. We argue on theoretical grounds that is indeed the most plausible general behaviour. 19 refs., 12 figs.
Date: January 1, 1990
Creator: Hagmann, C. & Sikivie, P.
Partner: UNT Libraries Government Documents Department

Parker limit for monopoles with large magnetic charge

Description: The survival of galactic magnetic fields places a limit on the flux of magnetic monopoles, the so-called ''Parker limit.'' Previous discussions of the Parker limit have assumed that the charge of the monopole is the Dirac value, g/sub Dirac/ = 2..pi../e. However, if the grand unified group is broken by Wilson lines, as is assumed in some superstring models, the minimum value of the magnetic charge is not the Dirac quantum, but an integer multiple of it. In this brief report we investigate the dependence of the Parker limit on the charge of the magnetic monopole. 10 refs., 1 fig.
Date: April 28, 1986
Creator: Hodges, H.M.; Kolb, E.W. & Turner, M.S.
Partner: UNT Libraries Government Documents Department

Particle physics and superstrings

Description: Implications of recent precision measurements of the standard model gauge coupling constants are discussed in the context of superstring theory. 40 refs.
Date: June 7, 1991
Creator: Gaillard, M.K. (California Univ., Berkeley, CA (United States). Dept. of Physics Lawrence Berkeley Lab., CA (United States))
Partner: UNT Libraries Government Documents Department

Introduction to string field theory. A pedestrian approach to the covariant formulation

Description: A relatively elementary account is given of what a string field represents and what is involved in the construction of its covariant action. Emphasis is on drawing a correspondence with similar problems in ordinary field theory and, particularly, using the language and mathematics used in ordinary field theory. Only the free string is discussed. 17 refs., 3 figs. (LEW)
Date: January 1, 1986
Creator: West, G.B.
Partner: UNT Libraries Government Documents Department

String perturbation theory and effective Lagrangians

Description: We isolate logarithmic divergences from bosonic string amplitudes on a disc. These divergences are compared with 'tadpole' divergences in the effective field theory with a cosmological term, which also contains an effective potential for the dilation. Also, corrections to ..beta..-functions are compared with variations of the effective action. In both cases we find an inconsistency between the two. This is a serious problem which could undermine our ability to remove divergences from the bosonic string.
Date: September 1, 1987
Creator: Klebanov, I.
Partner: UNT Libraries Government Documents Department

Superstrings and geometry of superspace

Description: These lectures present some recent developments in the sigma-model approach to the Green-Schwarzsuperstring. Among the topics included are: (1) interpretation of the free superstring as a flat superspace sigma-model; (2) propagation of the superstring in curved superspace; and (3) in the presence of background super Yang-Mills fields. The role of the world-sheet fermionic gauge symmetry needed to ensure consistent coupling to background fields is emphasized. 24 refs.
Date: May 1, 1986
Creator: Dhar, A.
Partner: UNT Libraries Government Documents Department