269 research outputs found
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 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
- …