Can Froissart Bound Explain Hadron Cross-Sections at High Energies?

Experimentally observed slow growth of hadron cross-sections at high energies is a very intriguing but poorly understood property of QCD. It is tempting to explain the slow growth by saturation of Froissart bound or another similar universal mechanism. We reconsider derivation of Froissart bound in QCD in chiral limit and argue it can not justify experimentally observed behavior. Although the conventional Froissart-Martin bound should impose non-trivial constraint on the growth of hadron cross-sections, because of the small value of pion masses it will become restrictive only at currently unaccessible center-of-mass energies exceeding $10^5-10^6$ GeV.Comment: 13 pages, 1 figure. v2: minor corrections, references adde

Tachyon-Free Non-Supersymmetric Strings on Orbifolds

We discuss tachyon-free examples of (Type IIB on) non-compact non-supersymmetric orbifolds. Tachyons are projected out by discrete torsion between orbifold twists, while supersymmetry is broken by a Scherk-Schwarz phase (+1/-1 when acting on space-time bosons/fermions) accompanying some even order twists. The absence of tachyons is encouraging for constructing non-supersymmetric D3-brane gauge theories with stable infrared fixed points. The D3-brane gauge theories in our orbifold backgrounds have chiral N = 1 supersymmetric spectra, but non-supersymmetric interactions.Comment: 17 page

Non-supersymmetric Conifold

We find a new family of non-supersymmetric numerical solutions of IIB supergravity which are dual to the N=1 cascading "conifold" theory perturbed by certain combinations of relevant single trace and marginal double trace operators with non infinitesimal couplings. The SUSY is broken but the resulting ground states, and their gravity duals, remain stable, at least perturbatively.Despite the complicated field theory dynamics the gravity solutions have a simple structure. They feature the Ricci-flat non-Kahler metric on the deformed conifold and the imaginary self-dual three-form flux accompanied by a constant dilaton.Comment: 27 pages, 6 figures; v2: minor corrections; v3: comments adde

Flavor brane on the baryonic branch of moduli space

We study an extra flavor in the cascading SU((k+1)M)xSU(k M) gauge theory by adding probe D7-brane to the geometry. By finding a solution to the kappa-symmetry equation we establish that the D7-brane is mutually supersymmetric with the background everywhere on the baryonic branch of moduli space. We also discuss possible applications of this result.Comment: 15 pages; v2 typo corrected, references adde

Large N Field Theory and AdS Tachyons

In non-supersymmetric orbifolds of N =4 super Yang-Mills, conformal invariance is broken by the logarithmic running of double-trace operators -- a leading effect at large N. A tachyonic instability in AdS_5 has been proposed as the bulk dual of double-trace running. In this paper we make this correspondence more precise. By standard field theory methods, we show that the double-trace beta function is quadratic in the coupling, to all orders in planar perturbation theory. Tuning the double-trace coupling to its (complex) fixed point, we find conformal dimensions of the form 2 + i b, as formally expected for operators dual to bulk scalars that violate the stability bound. We also show that conformal invariance is broken in perturbation theory if and only if dynamical symmetry breaking occurs. Our analysis is applicable to a general large N field theory with vanishing single-trace beta functions.Comment: 26 pages, 6 figures. v3: small changes, version published on JHEP

Perturbative Gauge Theory and Closed String Tachyons

We find an interesting connection between perturbative large N gauge theory and closed superstrings. The gauge theory in question is found on N D3-branes placed at the tip of the cone R^6/Gamma. In our previous work we showed that, when the orbifold group Gamma breaks all supersymmetry, then typically the gauge theory is not conformal because of double-trace couplings whose one-loop beta functions do not possess real zeros. In this paper we observe a precise correspondence between the instabilities caused by the flow of these double-trace couplings and the presence of tachyons in the twisted sectors of type IIB theory on orbifolds R^{3,1}x R^6/Gamma. For each twisted sectors that does not contain tachyons, we show that the corresponding double-trace coupling flows to a fixed point and does not cause an instability. However, whenever a twisted sector is tachyonic, we find that the corresponding one-loop beta function does not have a real zero, hence an instability is likely to exist in the gauge theory. We demonstrate explicitly the one-to-one correspondence between the regions of stability/instability in the space of charges under Gamma that arise in the perturbative gauge theory and in the free string theory. Possible implications of this remarkably simple gauge/string correspondence are discussed.Comment: 25 pages, Latex; V2: Clarifications and references adde

The Bethe Ansatz for Z_S Orbifolds of N=4 Super Yang-Mills Theory

Worldsheet techniques can be used to argue for the integrability of string theory on AdS_5xS^5/Z_S, which is dual to the strongly coupled Z_S-orbifold of N=4 SYM. We analyze the integrability of these field theories in the perturbative regime and construct the relevant Bethe equations.Comment: 16 page

I-odd sector of the Klebanov-Strassler theory

The Klebanov-Strassler background is invariant under the Z_2 symmetry I, which acts by exchanging the bi-fundamental fields A and B, accompanied by the charge conjugation. We study the background perturbations in the I-odd sector and find an exhaustive list of bosonic states invariant under the global SU(2)*SU(2) symmetry. In addition to the scalars identified in an earlier publication arXiv:0712.4404 we find 7 families of massive states of spin 1. Together with the spin 0 states they form 3 families of massive vector multiplets and 2 families of massive gravitino multiplets, containing a vector, a pseudovector and fermions of spin 3/2 and 1/2. In the conformal Klebanov-Witten case these I-odd particles belong to the N=1 superconformal Vector Multiplet I and Gravitino Multiplets II and IV. The operators dual to the I-odd singlet sector include those without bi-fundamental fields making an interesting connection with the pure N=1 SYM theory. We calculate the mass spectrum of the corresponding glueballs numerically and discuss possible applications of our results.Comment: 34 pages, 3 figures, 2 table