Anyon Mean Field as an Exact Limit of a Gauge Theory

We summarize a study of an Abelian gauge theory in 2+1 dimensions, the gauge field being coupled to nonrelativistic Fermions. The Action for the gauge field is a combination of the Maxwell term and a Chern-Simons (CS) term. We study the limit of vanishing Fermions' charge, keeping fixed the gauge field mass induced by the CS term. By considering a closed surface, in particular a torus to keep translational invariance, we show that the Fermions do not decouple completely from the gauge field, and in fact they behave as Anyons treated in the -translationally invariant formulation of the- Mean Field approximation. We describe the exact solution of this limiting case.Comment: 8 pages, LaTe

The decay of massive closed superstrings with maximum angular momentum

We study the decay of a very massive closed superstring (i.e. \alpha' M^2>> 1) in the unique state of maximum angular momentum. This is done in flat ten-dimensional spacetime and in the regime of weak string coupling, where the dominant decay channel is into two states of masses M_1, M_2. We find that the lifetime surprisingly grows with the first power of the mass M: T =c \alpha' M. We also compute the decay rate for each values of M_1, M_2. We find that, for large M, the dynamics selects only special channels of decay: modulo processes which are exponentially suppressed, for every decay into a state of given mass M_1, the mass M_2 of the other state is uniquely determined.Comment: 22 pages, 4 figure

Pair Production of Open Strings - Relativistic versus Dissipative Dynamics

We study the pair production of open strings in constant electric fields, using a general framework which encodes both relativistic string theory and generic linearly extended systems as well. In the relativistically invariant case we recover previous results, both for pair production and for the effective Born-Infeld action. We then derive a non-relativistic limit - where the propagation velocity along the string is much smaller than the velocity of light - obtaining quantum dissipation. We calculate the pair nucleation rate for this case, which could be relevant for applications.Comment: 22 pages; 1 LaTeX figur

Computing the R^4 term at two Superstring Loops

We use a previously derived integral representation for the four graviton amplitude at two loops in Superstring theory, whose leading term for vanishing momenta gives the two-loop contribution to the R^4 term in the Effective Action. We find by an explicit computation that this contribution is zero, in agreement with a general argument implying the vanishing of the R^4 term beyond one loop.Comment: 6 pages, Late

Long Lived Large Type II Strings: decay within compactification

Motivated also by recent revival of interest about metastable string states (as cosmic strings or in accelerator physics), we study the decay, in presence of dimensional compactification, of a particular superstring state, which was proven to be remarkably long-lived in the flat uncompactified scenario. We compute the decay rate by an exact numerical evaluation of the imaginary part of the one-loop propagator. For large radii of compactification, the result tends to the fully uncompactified one (lifetime T = const M^5/g^2), as expected, the string mainly decaying by massless radiation. For small radii, the features of the decay (emitted states, initial mass dependence,....) change, depending on how the string wraps on the compact dimensions.Comment: 32 pages, 24 text plus appendices, 4 figure

Semiclassical decay of strings with maximum angular momentum

We study the classical breaking of a highly excited (closed or open) string state on the leading Regge trajectory, represented by a rotating soliton solution, and we find the resulting solutions for the outgoing two pieces, describing two specific excited string states. This classical picture reproduces very accurately the precise analytical relation of the masses $M_1$ and $M_2$ of the decay products found in a previous quantum computation. The decay rate is naturally described in terms of a semiclassical formula. We also point out some interesting features of the evolution after the splitting process.Comment: 18 pages, latex, 7 figure

Decay of long-lived massive closed superstring states: Exact results

We find a one-parameter family of long-lived physical string states in type II superstring theory. We compute the decay rate by an exact numerical evaluation of the imaginary part of the one-loop propagator. Remarkably, the lifetime rapidly increases with the mass. We find a power-law dependence of the form $T = const. g^{-2} Mass^\alpha$, where the value of $\alpha$ depends on the parameter characterizing the state. For the most stable state in this family, one has $\alpha ~= 5$. The dominant decay channel of these massive string states is by emission of soft massless particles. The quantum states can be viewed semiclassically as closed strings which cannot break during the classical evolution.Comment: Latex, 5 figures, 35 pages (= 23 pages + appendices). Minor correction

Handbook on string decay

We explain simple semi-classical rules to estimate the lifetime of any given highly-excited quantum state of the string spectrum in flat spacetime. We discuss both the decays by splitting into two massive states and by massless emission. As an application, we study a solution describing a rotating and pulsating ellipse which becomes folded at an instant of time -- the ``squashing ellipse''. This string interpolates between the folded string with maximum angular momentum and the pulsating circular string. We explicitly compute the quantum decay rate for the corresponding quantum state, and verify the basic rules that we propose. Finally, we give a more general (4-parameter) family of closed string solutions representing rotating and pulsating elliptical strings.Comment: 18 pages, 9 figures. Final version appeared in JHE