Stringy Effects Research Articles

Dispersion relations in string theory

We analyze the analytic continuation of the formally divergent one-loop amplitude for scattering of the gravitonmultiplet in the Type II superstring. In particular we obtain explicit double and single dispersion relations, formulas for all the successive branch cuts extending out to +∞, as well as for the decay rate of a massive string state of arbitrary mass2N into two string states of lower mass. We compare our results with the box diagram in a superposition of φ3-like field theories. The stringy effects are traced to a convergence problem in this superposition.

STRINGY QUANTUM EFFECTS IN TWO-DIMENSIONAL BLACK HOLE

We discuss the classical two-dimensional black hole in the framework of the non-perturbative formulation (in terms of non-relativistic fermions) of c=1 string field theory. We identify an off-shell operator whose classical equation of motion is that of tachyon in the classical graviton-dilaton black hole background. The black hole ‘singularity’ is identified with the Fermi surface in the phase space of a single fermion, and as such is a consequence of the semiclassical approximation. An exact treatment reveals that stringy quantum effects wash away the classical singularity.

STRINGY EFFECTS ON SUPERSYMMETRY BREAKING IN LOW ENERGY SUPERGRAVITY THEORIES

The possibility of soft supersymmetry breaking at the tree level of string-inspired low energy supergravity theory is investigated. It is shown that the stringy quantum effects like the world sheet instanton and string loop effects can induce soft supersymmetry breakings at the tree level of the observable sector. Generic mass terms and trilinear soft breaking terms that arise are calculated.

On the concept of naturalness in string theories

We point out that string theory can provide an explanation for the vanishing of certain parameters in its low-energy limit which cannot be understood through the symmetries of the field-theoretic approximation. This fact may enable us to pinpoint stringy effects in the effective field theoretic limit.

Quark-lepton mass matrices in orbifold models

Quark-lepton mass matrices are studied in an orbifold model with three families of SU(3)×SU(2)×U(1) n . It is found that pure stringly effects cannot explain the mass hierarchy of quarks and leptons but can explain the smallness of mixing angles. Some constraints are required on R/ α′ and the vacuum expectation values of Higgs scalars in order to derive realistic values of the quark-lepton masses and the mixing angles. This model and some others predict the existence of pseudo-Goldstone bosons with masses derived from stringy effects.