416 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
Generalized Gibbs Ensemble of 2d CFTs at large central charge in the thermodynamic limit
We discuss partition function of 2d CFTs decorated by higher qKdV charges in
the thermodynamic limit when the size of the spatial circle goes to infinity.
In this limit the saddle point approximation is exact and at infinite central
charge generalized partition function can be calculated explicitly. We show
that leading 1/c corrections to free energy can be reformulated as a sum over
Young tableaux which we calculate for the first two qKdV charges. Next, we
compare generalized ensemble with the "eigenstate ensemble" that consists of a
single primary state. At infinite central charge the ensembles match at the
level of expectation values of local operators for any values of qKdV
fugacities. When the central charge is large but finite, for any values of the
fugacities the aforementioned ensembles are distinguishable.Comment: 23 page
Universality of fast quenches from the conformal perturbation theory
We consider global quantum quenches, a protocol when a continuous field
theoretic system in the ground state is driven by a homogeneous time-dependent
external interaction. When the typical inverse time scale of the interaction is
much larger than all relevant scales except for the UV-cutoff the system's
response exhibits universal scaling behavior. We provide both qualitative and
quantitative explanations of this universality and argue that physics of the
response during and shortly after the quench is governed by the conformal
perturbation theory around the UV fixed point. We proceed to calculate the
response of one and two-point correlation functions confirming and generalizing
universal scalings found previously. Finally, we discuss late time behavior
after the quench and argue that all local quantities will equilibrate to their
thermal values specified by an excess energy acquired by the system during the
quench.Comment: published version, refs added, minor typos corrected, 38 pages, no
fgiure
Universality of Quantum Information in Chaotic CFTs
We study the Eigenstate Thermalization Hypothesis (ETH) in chaotic conformal
field theories (CFTs) of arbitrary dimensions. Assuming local ETH, we compute
the reduced density matrix of a ball-shaped subsystem of finite size in the
infinite volume limit when the full system is an energy eigenstate. This
reduced density matrix is close in trace distance to a density matrix, to which
we refer as the ETH density matrix, that is independent of all the details of
an eigenstate except its energy and charges under global symmetries. In two
dimensions, the ETH density matrix is universal for all theories with the same
value of central charge. We argue that the ETH density matrix is close in trace
distance to the reduced density matrix of the (micro)canonical ensemble. We
support the argument in higher dimensions by comparing the Von Neumann entropy
of the ETH density matrix with the entropy of a black hole in holographic
systems in the low temperature limit. Finally, we generalize our analysis to
the coherent states with energy density that varies slowly in space, and show
that locally such states are well described by the ETH density matrix.Comment: 43 page
The application of the intersect index to quasilinear eigenfunction problems
First time the intersect index was applied to non-linear problems in L. Lusternick's research. This direction is investigating at voronezh school now [1,2]. Small eigenfunctions and its global branches was considered by the intersect index in [3-5]
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