COMPACTIFICATION AND ONE-LOOP GAUGE COUPLING CORRECTIONS IN HETEROTIC STRING THEORY (original) (raw)

Theoretical and Phenomenological Aspects of Superstring Theories

1998

Introduction CHAPTER 2 2 Compactification on Orbifolds 2.1 Toroidal Compactifications 2.2 General Theory of Orbifold Compactifications 2.3 Duality Symmetries CHAPTER 3 3 Aspects of Threshold Corrections to Low Energy Effective string Theories compactified on Orbifolds 1 where the invariant integral is given by ds 2 = −g µν (x)dx µ dx ν. 2 For n = 0 we have the point particle, for n = 1 we have the string, while for n = 2 we have the membrane and so on. . .. 3 See the footnote following 3.31. 4 Unoriented open and closed strings with N = 1 supersymmetry. 5 The ten dimensional N = 1 supergravity coupled to matter has anomalies coming from hegagon diagrams.

Navigating into the realm of Non-Supersymmetric String Theories

2016

For more than two decades, remarkable progress has been made in the construction of supersymmetric Standard Model-like theories from the heterotic string theory. In particular, considerable effort has been invested in studying the abundant phenomenological features of heterotic strings exhibiting N = 1 spacetime supersymmetry. At the same time, their non-supersymmetric counterparts have received little attention on the grounds that strings which do not exhibit spacetime supersymmetry admit large one-loop dilaton tadpoles, and are therefore unstable. Nonetheless, in this epoch of data acquisition from high-luminosity experiments, the observational absence of supersymmetry is striking. Consequently, non-supersymmetric theories receive a profound interest in the particle physics community. In this thesis, a class of non-supersymmetric, tachyon-free, four-dimensional string models is constructed via a string generalisation of Scherk-Schwarz compactification. Such models demonstrate grea...

N = 2 heterotic superstring and its dual theory in five dimensions

Nuclear Physics B, 1996

We study quantum effects in five dimensions in heterotic superstring theory compactified on K 3 × S 1 and analyze the conjecture that its dual effective theory is eleven-dimensional supergravity compactified on a Calabi-Yau threefold. This theory is also equivalent to type II superstring theory compactified on the same Calabi-Yau manifold, in an appropriate large volume limit. In this limit the conifold singularity disappears and is replaced by a singularity associated to enhanced gauge symmetries, as naïvely expected from the heterotic description. Furthermore, we exhibit the existence of additional massless states which appear in the strong coupling regime of the heterotic theory and are related to a different type of singular points on Calabi-Yau threefolds.

Supersymmetry among free fermions and superstrings

Physics Letters B, 1986

A complete classification is given of all supersymmetric theories of free massless two-dimensional fermions. This, in particular, implies a classification of all free-fermion representations of super Kac-Moody algebras. It is shown that these cannot be used to construct new string theories with unbroken supersymmetry in Minkowski space-time, other than the torus-compactifications of the known ten-dimensional superstrings. Assuming anti-de-Sitter space-time could -restore conformal invariance, it is shown how one could construct a string theory whose low-lying excitations form a multiplet of gauged N = 8 supergravity.

On non-renormalization theorems for four-dimensional superstrings

Physics Letters B, 1989

For d=4, N= 1 supersymmetric string theories we compute the quantum corrections to the superpotential to two-loop order. The vanishing of the amplitudes relies crucially on generalized Riemann identities. Beyond genus one, these map to non-trivial zeroes oftheta functions implied by the Riemann vanishing theorem.

Fermion masses in E8 × E′8 superstring theories

Physics Letters B, 1986

We consider string theories with gauge group E s × E~ compactffled on Calabl-Yau manifolds so that the umfled gauge group ts E 6 ×E' 8. If the fermlon content as N r 27+ 8(27+27), where 8 =1 or 2, and the E 6 IS broken by Wilson loops to a gauge group E (which contains SU(3)~ × SU(2)L × U(1)v), then E is specified almost uniquely ff we require that neither the up nor the down quark mass matrices are Ldentlcally zero at tree level and that the Htggs doublets arise wa the incomplete multlplet mechamsm In parncular, ~ must be rank 6 However, ff we wish for the neutral mass matrix to be acceptable, we must have the electron mass matnx identically zero at tree level We comment on a way to possibly have small (but non-zero) neutrino masses m superstrmg models

(8,0) Quantum mechanics and symmetry enhancement in type I' superstrings

Journal of High Energy Physics, 1998

The low-energy supersymmetric quantum mechanics describing D-particles in the background of D8-branes and orientifold planes is analyzed in detail, including a careful discussion of Gauss' law and normal ordering of operators. This elucidates the mechanism that binds Dparticles to an orientifold plane, in accordance with the predictions of heterotic/type I duality. The ocurrence of enhanced symmetries associated with massless bound states of a D-particle with one orientifold plane is illustrated by the enhancement of SO(14) × U (1) to E 8 and SO(12) × U (1) to E 7 at strong type I' coupling. Enhancement to higher-rank groups involves both orientifold planes. For example, the enhanced E 8 ×E 8 ×SU (2) symmetry at the self-dual radius of the heterotic string is seen as the result of two D8-branes coinciding midway between the orientifold planes, while the enhanced SU (18) symmetry results from the coincidence of all sixteen D8-branes and SO(34) when they also coincide with an orientifold plane. As a separate by-product, the s-rule of brane-engineered gauge theories is derived by relating it through a chain of dualities to the Pauli exclusion principle.

Higher Dimensional Superstring Theories

2004

In this paper we study the matter form of the conformal and super-conformal ghosts action. The ghosts fields also will be expressed in terms of some scalar and spinor fields. The Poincaré-like symmetries and various supersymmetries of this covariant action are analyzed. The N = 2 supersymmetry gives 10+2 signature for the target space of the superstring theory. In addition, the signature 11+3 for the target spacetime also is possible. PACS: 11.25.-w