Yuri Kubyshin

Effective Lagrangians for physical degrees of freedom in the Randall–Sundrum model

We derive the second variation Lagrangian of the Randall–Sundrum model with two branes, study its gauge invariance and diagonalize it in the unitary gauge. We also show that the effective four-dimensional theory looks different on different branes and calculate the observable mass spectra and the couplings of the physical degrees of freedom of five-dimensional gravity to matter.

Gradient Flows From An Approximation To The Exact Renormalization Group

Through appropriate projections of an exact renormalization group equation, we study fixed points, critical exponents and nontrivial renormalization group flows in scalar field theories in 2 < D < 4. THE STANDARD UPPER CRITICAL DIMENSIONS D k = 2k/(k − 1), k = 2, 3, 4,... appear naturally encoded in our formalism, and for dimensions smaller but very close to d k our results match the e-expansion. Within the coupling constant subspace of mass and quartic couplings and for any d, we find a gradient flow with two fixed points determined by a positive-definite metric and a c-function which is monotonically decreasing along the flow

EXACT RENORMALIZATION GROUP STUDY OF FERMIONIC THEORIES

Abstract The exact renormalization group approach (ERG) is developed for the case of pure fermionic theories by deriving a Grassmann version of the ERG equation and applying it to the study of fixed point solutions and critical exponents of the two-dimensional chiral Gross-Neveu model. An approximation based on the derivative expansion and a further truncation in the number of fields is used. Two solutions are obtained analytically in the limit N → ∞, with N being the number of fermionic species. For finite N some fixed point solutions, with their anomalous dimensions and critical exponents, are computed numerically. The issue of separation of physical results from the numerous spurious ones is discussed. We argue that one of the solutions we find can be identified with that of Dashen and Frishman, whereas the others seem to be new ones.

Is the string coupling constant invariant under T duality

Abstract It is well known that under T-duality the sigma model dilaton (which is normally though to be related to the string coupling constant through the simple formula κ = exp ), undergoes an additional shift. On the other hand, Kugo and Zwiebach, using a simplified form of string field theory, claim that the string coupling constant does not change under the T-duality. Obviously, what seems to happen is that two different coupling constants, associated to different dilatons, are used. In this contribution we shall try to clarify this, and related issues.