252 research outputs found
Classical Black Hole Production In Quantum Particle Collisions
The semiclassical picture of black hole production in trans-Planckian
elementary particle collisions is reviewed.Comment: 5 pages, 7 figures; talk given at the 6th Alexander Friedmann
International Seminar on Gravitation and Cosmology, Cargese, France, June
28-July 3, 2004; to appear in the proceedings (Int.J.Mod.Phys.A); v2: typos
correcte
Thermal production of gravitinos
We reconsider thermal production of gravitinos in the early universe, adding to previously considered 2 -> 2 gauge scatterings: a) production via 1 -> 2 decays, allowed by thermal masses; b) the effect of the top Yukawa coupling; c) a proper treatment of the reheating process. Our final result behaves physically (larger couplings give a larger rate) and is twice larger than previous results, implying e.g. a twice stronger constraint on the reheating temperature. Accessory results about (supersymmetric) theories at finite temperature and gravitino couplings might have some interest
Universal constraints on conformal operator dimensions
We continue the study of model-independent constraints on the unitary conformal field theories (CFTs) in four dimensions, initiated in. Our main result is an improved upper bound on the dimension Δ of the leading scalar operator appearing in the operator product expansion (OPE) of two identical scalars of dimension d: φ d≠1+O δ+.... In the interval 1<1.7 this universal bound takes the form Δ≤2+0.7(d-1)1/2+2. 1(d-1)+0.43(d-1)3/2. The proof is based on prime principles of CFT: unitarity, crossing symmetry, OPE, and conformal block decomposition. We also discuss possible applications to particle phenomenology and, via a 2D analogue, to string theory. © 2009 The American Physical Society
What can the information paradox tell us about the early Universe?
In recent years we have come to understand how the information paradox is
resolved in string theory. The huge entropy of black
holes is realized by an explicit set of horizon sized `fuzzball' wavefunctions.
The wavefunction of a collapsing shell spreads relatively quickly over this
large phase space of states, invalidating the classical black hole geometry the
shell would have created. We argue that a related effect may occur in the early
Universe. When matter is crushed to high densities we can access a similarly
large phase space of gravitational `fuzzball' solutions. While we cannot
estimate specific quantities at this point, a qualitative analysis suggests
that spreading over phase space creates an extra `push' expanding the Universe
to larger volumes.Comment: 6 pages, 3 figures (Essay awarded second prize in the Gravity
Research Foundation essay competition 2012
Processing of chloride-containing productive solutions after uranium in situ leaching by ion exchange method
The uranium sorption from productive solutions containing chloride ions using anion-exchange resins was investigated. The VPAE ion exchanger had the highest values of the sorption capacity, which for the experiment in the static mode was 13 kg U m -3 , and for the experiment in the dynamic mode, it was equal to 36 kg U m -3 . The use of VPAE anion exchanger will make it possible for uranium recovery from productive solutions with an increased content of chloride without sacrificing the productivity of the sorption plant. The process of saturated resins regeneration by various reagents was investigated. The use of ammonium nitrate solution with sulfuric acid ensured maximum value of uranium recovery from the saturated resin phase (76-97%). © 2019, Gadjah Mada University. All rights reserved
Bounding scalar operator dimensions in 4D CFT
In an arbitrary unitary 4D CFT we consider a scalar operator \phi, and the operator \phi^2 defined as the lowest dimension scalar which appears in the OPE \phi\times\phi with a nonzero coefficient. Using general considerations of OPE, conformal block decomposition, and crossing symmetry, we derive a theory-independent inequality [\phi^2] \leq f([\phi]) for the dimensions of these two operators. The function f(d) entering this bound is computed numerically. For d->1 we have f(d)=2+O(\sqrt{d-1}), which shows that the free theory limit is approached continuously. We perform some checks of our bound. We find that the bound is satisfied by all weakly coupled 4D conformal fixed points that we are able to construct. The Wilson-Fischer fixed points violate the bound by a constant O(1) factor, which must be due to the subtleties of extrapolating to 4-\epsilon dimensions. We use our method to derive an analogous bound in 2D, and check that the Minimal Models satisfy the bound, with the Ising model nearly-saturating it. Derivation of an analogous bound in 3D is currently not feasible because the explicit conformal blocks are not known in odd dimensions. We also discuss the main phenomenological motivation for studying this set of questions: constructing models of dynamical ElectroWeak Symmetry Breaking without flavor problems
Bounding scalar operator dimensions in 4D CFT
In an arbitrary unitary 4D CFT we consider a scalar operator φ, and the operator φ2 defined as the lowest dimension scalar which appears in the OPE φ × φ with a nonzero coefficient. Using general considerations of OPE, conformal block decomposition, and crossing symmetry, we derive a theory-independent inequality [φ2] f([φ]) for the dimensions of these two operators. The function f(d) entering this bound is computed numerically. For d1 we have f(d) = 2+O((d-1)1/2), which shows that the free theory limit is approached continuously. We perform some checks of our bound. We find that the bound is satisfied by all weakly coupled 4D conformal fixed points that we are able to construct. The Wilson-Fischer fixed points violate the bound by a constant O(1) factor, which must be due to the subtleties of extrapolating to 4- dimensions. We use our method to derive an analogous bound in 2D, and check that the Minimal Models satisfy the bound, with the Ising model nearly-saturating it. Derivation of an analogous bound in 3D is currently not feasible because the explicit conformal blocks are not known in odd dimensions. We also discuss the main phenomenological motivation for studying this set of questions: constructing models of dynamical ElectroWeak Symmetry Breaking without flavor problems. © 2008 SISSA
An isoperimetric inequality for the fundamental tone of free plates
We establish an isoperimetric inequality for the fundamental tone (first
nonzero eigenvalue) of the free plate of a given area, proving the ball is
maximal. Given , the free plate eigenvalues and eigenfunctions
are determined by the equation
together with certain natural boundary conditions. The boundary conditions are
complicated but arise naturally from the plate Rayleigh quotient, which
contains a Hessian squared term . We adapt Weinberger's method from
the corresponding free membrane problem, taking the fundamental modes of the
unit ball as trial functions. These solutions are a linear combination of
Bessel and modified Bessel functions.Comment: 27 pages. In preparation
Universal constraints on conformal operator dimensions
We continue the study of model-independent constraints on the unitary conformal field theories (CFTs) in four dimensions, initiated in [R. Rattazzi, V. S. Rychkov, E. Tonni, and A. Vichi, J. High Energy Phys. 12 (2008) 031]. Our main result is an improved upper bound on the dimension Delta of the leading scalar operator appearing in the operator product expansion (OPE) of two identical scalars of dimension d: phi(d)x phi(d)=1+O-Delta+.... In the interval 1 < d < 1.7 this universal bound takes the form Delta < 2+0.7(d-1)(1/2)+2.1(d-1)+0.43(d-1)(3/2). The proof is based on prime principles of CFT: unitarity, crossing symmetry, OPE, and conformal block decomposition. We also discuss possible applications to particle phenomenology and, via a 2D analogue, to string theory
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