Search results for "string"
showing 10 items of 381 documents
Finite Quantum Gravity Amplitudes: No Strings Attached
2020
We study the gravity-mediated scattering of scalar fields based on a parameterisation of the Lorentzian quantum effective action. We demonstrate that the interplay of infinite towers of spin zero and spin two poles at imaginary squared momentum leads to scattering amplitudes that are compatible with unitarity bounds, causal, and scale-free at trans-Planckian energy. Our construction avoids introducing non-localities or the massive higher-spin particles that are characteristic in string theory.
Kaluza-Klein origin for the superstring tension
1992
The natural configuration space of a string in a background antisymmetric tensor potential is not loop space, but a principal U(1) bundle over loop space. This allows a Kaluza-Klein--like interpretation of the string tension as momentum along the U(1) fiber, and a similar interpretation is possible for a {ital p}-dimensional object. The higher-dimensional'' action incorporating this momentum as a dynamical variable is given for a {ital p}-dimensional supersymmetric extended object, in a general supergravity background. Its relevance, for a flat background, to classical anomalies'' in the supersymmetry algebra is explained.
Quasidisks and string theory
1990
Abstract A heuristic model of non-perturbative bosonic string theory on the Bers universal Teichmuller space of normalized quasidisks is discussed. It is suggested that the infinite-dimensional analogue of the Polyakov energy might be the quasidisk area.
Supersymmetry currents and WZ-like terms in (supersymmetry)2 models
1990
Abstract Using the superfield formulation of the N = 1 spinning superparticle model as an example, the superfield currents associated with the target space supersymmetry are given, and the component expression of the corresponding superalgebra is found to describe a graded “doubling” of the Poincare superalgebra. Further, it is shown how the torsion-like term in the spinning super-particle model can be obtained from the form associated with the Green-Schwarz WZ term for the superstring, and a possible way of introducing extended spinning supersymmetric objects is discussed.
Leptonic CP violation with massless neutrinos
1989
Abstract Leptonic CP violation may arise in the SU(2) ⊗ U(1) theory even if the neutrinos are strictly massless and, as a result, it is potentially large. Theoretical scenarios include isosinglet neutral heavy leptons which are present in many extensions of the standard electroweak theory such as superstring inspired models. We discuss in detail the nature of this CP violation and show that it can occur in a two-generation model. Possible effects are briefly discussed.
Canonical equivalence of a generic 2-D dilaton gravity model and a free field
1997
We show that a canonical transformation converts, up to a boundary term, a generic 2-D dilaton gravity model into a free field theory with a Minkowskian target space.
String fields as limit of functions and surface terms in string field theory
1989
We consider the String Field Theory proposed by Witten in the discretized approach, where the string is considered as the limit N → ∞ of a collection of N points. In this picture the string functional is the limit of a succession of functions of an increasing number of variables; an object with some resemblances to distributions. Attention is drawn to the fact that the convergence is not of the uniform kind, and that therefore exchanges of limits, sums and integral signs can cause problems, and be ill defined. In this context we discuss some surface terms found by Woodard, which arise in integrations by parts, and argue that they depend crucially on the choice of the successions of functio…
THE SPACE OF STRING CONFIGURATIONS IN STRING FIELD THEORY
1990
In this paper we consider the set of maps from the interval [0, π] which constitute the argument of the functionals of a String Field Theory. We show that in order to correctly reproduce results of the dual model one has to include all square integrable functions in the functional integral, or Ω0 in terms of Sobolev spaces.
Energy of string loops and thermodynamics of dark energy
2011
We discuss the thermodynamic aspects of a simple model of cosmic string loops, whose energy is nonlinearly related to their lengths. We obtain in a direct way an equation of state having the form p=-(1+{alpha}){rho}/3, with {rho} the energy density and 1+{alpha} the exponent which relates the energy u{sub l} of a loop with its length l as u{sub l}{approx}l{sup 1+{alpha}}. In the linear situation ({alpha}=0) one has p=-{rho}/3, in the quadratic one ({alpha}=1) p=-2{rho}/3, and in the cubic case ({alpha}=2) p=-{rho}. For all values of {alpha} the entropy goes as S{approx}(2-{alpha})L{sup 3/2} (L being the string length density). The expression of S is useful to explore the behavior of such st…
Simplicial Quantum Gravity on a Randomly Triangulated Sphere
1999
We study 2D quantum gravity on spherical topologies employing the Regge calculus approach with the dl/l measure. Instead of the normally used fixed non-regular triangulation we study random triangulations which are generated by the standard Voronoi-Delaunay procedure. For each system size we average the results over four different realizations of the random lattices. We compare both types of triangulations quantitatively and investigate how the difference in the expectation value of the squared curvature, $R^2$, for fixed and random triangulations depends on the lattice size and the surface area A. We try to measure the string susceptibility exponents through finite-size scaling analyses of…