280 research outputs found
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
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
Breathing Oscillations in Bose - Fermi Mixing Gases with Yb atoms in the Largely Prolate Deformed Traps
We study the breathing oscillations in bose-fermi mixtures with Yb isotopes
in the largely prolate deformed trap, which are realized by Kyoto group. We
choose the three combinations of the Yb isotopes, Yb170-Yb171, Yb170-Yb173 and
Yb174-Yb173, whose boson-fermion interactions are weakly repulsive, strongly
attractive and strongly repulsive. The collective oscillations in the deformed
trap are calculated in the dynamical time-development approach, which is
formulated with the time-dependent Gross-Pitaevskii and the Vlasov equations.
We analyze the results in the time-development approach with the intrinsic
oscillation modes of the deformed system, which are obtained using the scaling
method, and show that the damping and forced-oscillation effects of the
intrinsic modes give time-variation of oscillations, especially, in the fermion
transverse mode.Comment: 27 pages, 12 figure
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
Free expansion of fermionic dark solitons in a boson-fermion mixture
We use a time-dependent dynamical mean-field-hydrodynamic model to study the
formation of fermionic dark solitons in a trapped degenerate fermi gas mixed
with a Bose-Einstein condensate in a harmonic as well as a periodic
optical-lattice potential. The dark soliton with a "notch" in the probability
density with a zero at the minimum is simulated numerically as a nonlinear
continuation of the first vibrational excitation of the linear
mean-field-hydrodynamic equations, as suggested recently for pure bosons. We
study the free expansion of these dark solitons as well as the consequent
increase in the size of their central notch and discuss the possibility of
experimental observation of the notch after free expansion.Comment: 14 pages, 6 figure
Sterol metabolism modulates susceptibility to HIV-1 Infection
Background: 25-hydroxylase (CH25H) is an Interferon stimulated gene (ISG), which catalyzes the synthesis of 25-Hydroxycholesterol (25HC). 25HC intervenes in metabolic and infectious processes as controls cholesterol homeostasis and influences viral entry into host cells.We verified whether natural resistance to HIV-1 infection in HIV-1-exposed seronegative (HESN) individuals is at least partially mediated by particularities in sterol biosynthesis.
Methods: Peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages (MDMs) isolated from 15 sexually-exposed HESN and 15 healthy controls (HC) were in vitro HIV-1-infected and analyzed for: 1) percentage of IFN\u3b1-producing plasmacytoid Dendritic Cells (pDCs); 2) Cholesterol signaling and inflammatory response RNA expression; 3) resistance to HIV-1 infection. MDMs from 5 HC were in vitro HIV-1-infected in the absence/presence of exogenously added 25HC.
Results: IFN\u3b1-producing pDCs were augmented in HESN compared to HCs both in unstimulated and in in vitro HIV-1-infected PBMCs (p<0.001). An increased expression of CH25H and of a number of genes involved in cholesterol metabolism (ABCA1, ABCG1, CYP7B1, LXR\u3b1, OSBP, PPAR\u3b3, SCARB1) was observed as well; this, was associated with a reduced susceptibility to in vitro HIV-1-infection of PBMCs and MDMs (p<0.01). Notably, addition of 25HC to MDMs resulted in increased cholesterol efflux and augmented resistance to in vitro HIV-1-infection.
Conclusions: Results herein show that in HESN sterol metabolism might be particularly efficient. This could be related to the activation of the IFN\u3b1 pathway and results into a reduced susceptibility to in vitro HIV-1 infection. These results suggest a possible basis for therapeutic interventions to modulate HIV-1 infection
Excess energy of an ultracold Fermi gas in a trapped geometry
We have analytically explored finite size and interparticle interaction
corrections to the average energy of a harmonically trapped Fermi gas below and
above the Fermi temperature, and have obtained a better fitting for the excess
energy reported by DeMarco and Jin [Science , 1703 (1999)]. We
have presented a perturbative calculation within a mean field approximation.Comment: 8 pages, 4 figures; Accepted in European Physical Journal
Pauli Blocking of Collisions in a Quantum Degenerate Atomic Fermi Gas
We have produced an interacting quantum degenerate Fermi gas of atoms
composed of two spin-states of magnetically trapped K. The relative
Fermi energies are adjusted by controlling the population in each spin-state.
Measurements of the thermodynamics reveal the resulting imbalance in the mean
energy per particle between the two species, which is as large as a factor of
1.4 at our lowest temperature. This imbalance of energy comes from a
suppression of collisions between atoms in the gas due to the Pauli exclusion
principle. Through measurements of the thermal relaxation rate we have directly
observed this Pauli blocking as a factor of two reduction in the effective
collision cross-section in the quantum degenerate regime.Comment: 11 pages, 4 figure
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