Holographic Conformal Window - A Bottom Up Approach

We propose a five-dimensional framework for modeling the background geometry associated to ordinary Yang-Mills (YM) as well as to nonsupersymmetric gauge theories possessing an infrared fixed point with fermions in various representations of the underlying gauge group. The model is based on the improved holographic approach, on the string theory side, and on the conjectured all-orders beta function for the gauge theory one. We first analyze the YM gauge theory. We then investigate the effects of adding flavors and show that, in the holographic description of the conformal window, the geometry becomes AdS when approaching the ultraviolet and the infrared regimes. As the number of flavors increases within the conformal window we observe that the geometry becomes more and more of AdS type over the entire energy range.Comment: 20 Pages, 3 Figures. v2: references adde

Thermodynamics of deformed AdS5_5 model with a positive/negative quadratic correction in graviton-dilaton system

By solving the Einstein equations of the graviton coupling with a real scalar dilaton field, we establish a general framework to self-consistently solve the geometric background with black-hole for any given phenomenological holographic models. In this framwork, we solve the black-hole background, the corresponding dilaon field and the dilaton potential for the deformed AdS$_5$ model with a positive/negative quadratic correction. We systematically investigate the thermodynamical properties of the deformed AdS$_5$ model with a positive and negative quadratic correction, respectively, and compare with lattice QCD on the results of the equation of state, the heavy quark potential, the Polyakov loop and the spatial Wilson loop. We find that the bulk thermodynamical properties are not sensitive to the sign of the quadratic correction, and the results of both deformed holographic QCD models agree well with lattice QCD result for pure SU(3) gauge theory. However, the results from loop operators favor a positive quadratic correction, which agree well with lattice QCD result. Especially, the result from the Polyakov loop excludes the model with a negative quadratic correction in the warp factor of ${\rm AdS}_5$.Comment: 26 figures,36 pages,V.3: an appendix,more equations and references added,figures corrected,published versio

Target fragmentation in pp, ep and gamma p collisions at high energies

We calculate target fragmentation in pp --> nX and gamma p --> nX reactions in the meson cloud picture of the nucleon. The pp --> nX reaction is used to fix the pn pi(+) form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and, small x(Bj) electroproduction of forward neutrons at HERA. Here the q-qbar dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the hadronic reaction. For deep inelastic events (Q(2) > 10 GeV2) screening is weaker but still present at large Q2. The signature for this absorptive rescattering: is a shift of the d sigma/dE(n) distribution to higher neutron energies for photofragmentation

Renormalization group approach to the phase diagram of strong interaction

We examine the chiral phase transition of strong interaction within a linear sigma-model with two light quark flavors. Going beyond previous mean field analyses of the phase diagram, we derive an analytic renormalization group flow equation for the thermodynamic potential including mesonic fluctuations

Soft and hard Pomeron in the structure function of the proton at low x and low Q(2)

We study inclusive electroproduction on the proton at low x and low Q(2) using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model; in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, F2 proportional to x^(-lambda), proposed by Lopez and Yndurain. This extension allows to consider both the case Q(2) = 0 and the region of higher Q(2) on the basis of the same parametrization. A good simultaneous fit to the data on F2 and on the cross section sigma(gamma p) of real photoproduction is obtained for lambda = 0.37. With four parameters we achieve a chi(2)/d.o.f. = 0.98 for 222 data points. In addition, we use our model of the inclusive gamma*p interaction to compute the longitudinal structure function F(L)

Renormalization group flow in large N-c

We calculate renormalization group flow equations for the linear sigma-model in large N-c approximation. The flow equations decouple and can be solved analytically. The solution is equal to a self consistent solution of the NJL model in the same approximation, which shows that flow equations are a promising method to extend the calculation to higher order in 1/N-c. Including explicit chiral symmetry breaking, the large N-c approximation describes physics reasonably well. We further compare the analytic solution to the usually used polynomial truncation and find consistency. (C) 2002 Elsevier Science B.V. All rights reserved