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-loopâ€¦ (More)

A highly excited (closed or open) string state on the leading Regge trajectory can be represented by a rotating soliton solution. There is a semiclassical probability per unit cycle that this stringâ€¦ (More)

In ten dimensional type II superstring, all perturbative massive states are unstable, typically with a short lifetime compared to the string scale. We find that the lifetime of the average stringâ€¦ (More)

We explain simple semi-classical rules to estimate the lifetime of any given highlyexcited quantum state of the string spectrum in flat spacetime. We discuss both the decays by splitting into twoâ€¦ (More)

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 aâ€¦ (More)

We compare the vortex-like solutions of two different theories in (2 + 1) dimensions. In the first a nonrelativistic field self-interacts through a Chern-Simons gauge connection. It is P and Tâ€¦ (More)

We present a manifestly SO(8) invariant non-linear Lagrangian for describing the non-abelian dynamics of the bosonic degrees of freedom of N coinciding M2 branes in flat spacetime. The theoryâ€¦ (More)

We study the decay of a very massive closed superstring (i.e. Î±â€²M2 â‰« 1) in the unique state of maximum angular momentum. This is done in flat ten-dimensional spacetime and in the regime of weakâ€¦ (More)

In brane world string models with large extra dimensions, there are processes where fermion and antifermion (or two gluons) can annihilate producing a light particle (e.g. gluon) carrying transverseâ€¦ (More)

We use a previously derived integral representation for the four graviton amplitude at two loops in Super-string theory, whose leading term for vanishing momenta gives the two-loop contribution toâ€¦ (More)