21 research outputs found
Casimir interaction of finite-width strings
Within the trln-formalism we investigate the vacuum interaction of cosmic
strings and the influence of strings width on this effect. For the massless
real scalar field we compute the Casimir contribution into the total vacuum
energy. The dimensional-regularization technique is used. It is shown that the
regularized Casimir term contains neither the UV-divergences, nor the
divergences related with the non-integrability of the renormalized vacuum mean
of the energy-momentum tensor.Comment: 3 figure
Classical ultra-relativistic scattering in ADD
The classical differential cross-section is calculated for high-energy
small-angle gravitational scattering in the factorizable model with toroidal
extra dimensions. The three main features of the classical computation are: (a)
It involves summation over the infinite Kaluza-Klein towers but, contrary to
the Born amplitude, it is finite with no need of an ultraviolet cutoff. (b) It
is shown to correspond to the non-perturbative saddle-point approximation of
the eikonal amplitude, obtained by the summation of an infinite number of
ladder graphs of the quantum theory. (c) In the absence of extra dimensions it
reproduces all previously known results.Comment: 12 pages, minor change
Cysteine residues 244 and 458-459 within the catalytic subunit of Na,K-ATPase control the enzyme's hydrolytic and signaling function under hypoxic conditions
Our previous findings suggested that reversible thiol modifications of cysteine residues within the actuator (AD) and nucleotide binding domain (NBD) of the Na,K-ATPase may represent a powerful regulatory mechanism conveying redox- and oxygen-sensitivity of this multifunctional enzyme. S-glutathionylation of Cys244 in the AD and Cys 454-458-459 in the NBD inhibited the enzyme and protected cysteines' thiol groups from irreversible oxidation under hypoxic conditions. In this study mutagenesis approach was used to assess the role these cysteines play in regulation of the Na,K-ATPase hydrolytic and signaling functions. Several constructs of mouse α1 subunit of the Na,K-ATPase were produced in which Cys244, Cys 454-458-459 or Cys 244-454-458-459 were replaced by alanine. These constructs were expressed in human HEK293 cells. Non-transfected cells and those expressing murine α1 subunit were exposed to hypoxia or treated with oxidized glutathione (GSSG). Both conditions induced inhibition of the wild type Na,K-ATPase. Enzymes containing mutated mouse α1 lacking Cys244 or all four cysteines (Cys 244-454-458-459) were insensitive to hypoxia. Inhibitory effect of GSSG was observed for wild type murine Na,K-ATPase, but was less pronounced in Cys454-458-459Ala mutant and completely absent in the Cys244Ala and Cys 244-454-458-459Ala mutants. In cells, expressing wild type enzyme, ouabain induced activation of Src and Erk kinases under normoxic conditions, whereas under hypoxic conditions this effect was inversed. Cys454-458-459Ala substitution abolished Src kinase activation in response to ouabain treatment, uncoupled Src from Erk signaling, and interfered with O2-sensitivity of Na,K-ATPase signaling function. Moreover, modeling predicted that S-glutathionylation of Cys 458 and 459 should prevent inhibitory binding of Src to NBD. Our data indicate for the first time that cysteine residues within the AD and NBD influence hydrolytic as well as receptor function of the Na,K-ATPase and alter responses of the enzyme to hypoxia or upon treatment with cardiotonic steroids
Transplanckian bremsstrahlung and black hole production
Classical gravitational bremsstrahlung in particle collisions at
transplanckian energies is studied in .
The radiation efficiency is
computed in terms of the Schwarzschild radius , the impact
parameter and the Lorentz factor and found to be
, larger than previous
estimates by many powers of . The result is reliable for
impact parameters in the overlap of , with
marking (for ) the loss of the notion of classical trajectories
and the Compton length of the scattered particles.
The condition on and for extreme radiation damping and (presumably) no
black hole production is also derived.Comment: 4 pages, revtex 4. The discussion section is changed to better
clarify the region of validity of our calculation. The physical conclusions
and the abstract are modified accordingly. A few more references added. We
just added the preprint number CCTP-2010-1
Vacuum polarization and classical self-action near higher-dimensional defects
We analyze the gravity-induced effects associated with a massless scalar field in a higher-dimensional spacetime being the tensor product of -dimensional Minkowski space and n-dimensional spherically/cylindrically symmetric space with a solid/planar angle deficit. These spacetimes are considered as simple models for a multidimensional global monopole (if ) or cosmic string (if ) with flat extra dimensions. Thus, we refer to them as conical backgrounds. In terms of the angular-deficit value, we derive the perturbative expression for the scalar Green function, valid for any and , and compute it to the leading order. With the use of this Green function we compute the renormalized vacuum expectation value of the field square and the renormalized vacuum averaged of the scalar-field energy-momentum tensor for arbitrary d and n from the interval mentioned above and arbitrary coupling constant to the curvature . In particular, we revisit the computation of the vacuum polarization effects for a non-minimally coupled massless scalar field in the spacetime of a straight cosmic string. The same Green function enables to consider the old purely classical problem of the gravity-induced self-action of a classical point-like scalar or electric charge, placed at rest at some fixed point of the space under consideration. To deal with divergences, which appear in consideration of the two problems, we apply the dimensional-regularization technique, widely used in quantum field theory. The explicit dependence of the results upon the dimensionalities of both the bulk and conical submanifold is discussed