Tunneling into Extra Dimension and High-Energy Violation of Lorentz Invariance

We consider a class of models with infinite extra dimension, where bulk space does not possess SO(1,3) invariance, but Lorentz invariance emerges as an approximate symmetry of the low-energy effective theory. In these models, the maximum attainable speeds of the graviton, gauge bosons and scalar particles are automatically equal to each other and smaller than the maximum speed in the bulk. Additional fine-tuning is needed in order to assure that the maximum attainable speed of fermions takes the same value. A peculiar feature of our scenario is that there are no truly localized modes. All four-dimensional particles are resonances with finite widths. The latter depends on the energy of the particle and is naturally small at low energies.Comment: 21 pages, references and comments added, final version to appear in JHE

Physical degrees of freedom in stabilized brane world models

We consider brane world models with interbrane separation stabilized by the Goldberger-Wise scalar field. For arbitrary background, or vacuum configurations of the gravitational and scalar fields in such models, we construct the second variation Lagrangian, study its gauge invariance, find the corresponding equations of motion and decouple them in a suitable gauge. We also derive an effective four-dimensional Lagrangian for such models, which describes the massless graviton, a tower of massive gravitons and a tower of massive scalars. It is shown that for a special choice of the background solution the masses of the graviton excitations may be of the order of a few TeV, the radion mass of the order of 100 GeV, the inverse size of the extra dimension being tens of GeV. In this case the coupling of the radion to matter on the negative tension brane is approximately the same as in the unstabilized model with the same values of the fundamental five-dimensional energy scale and the interbrane distance.Comment: 17 pages, LaTeX, corrected typos, amended the normalization constants of the scalar modes and their coupling constants to matte

Current sheath studies by magnetic probes on plasma focus PF-400

The time resolved studies of the current sheath formation in a plasma focus discharge of Filippov type with energy stored in capacitors 60 kJ and maximum current 0.9 MA are presented. The current data received by two magnetic probes placed at radii 15 cm and 20 cm were compared with the total current detected by Rogovsky loop. It was found out in discharges with low neutron yield the formation of the extra current sheathes following one after another in 1-th, 2-th and even 3-th half-period of discharge. The single current sheath was observed in the discharges with the high neutron yield. The absolute current measurements showed that the whole discharge current goes throw paraxial area r < 15 cm during the phase of radial implosion, but at the instant of the peculiarity on the current derivative it is no more then half of value of total current. The value of the pinch current remains under the question.Проведено дослідження струмової оболонки плазмового фокуса філіпповського типу з енергетикою 60 кДж та максимальним струмом 0.9 МА. В експерименті порівнювались одночасні покази повного струму розряду від пояса Роговського й струмів, які реєструються двома магнітними зондами всередині приосьової області R < 20 см й R < 15 см. Спостережено наявність других й третіх струмових оболонок, наступних за першою, у пострілах з низьким нейтронним виходом. За умови нормального виходу існує тільки одна струмова оболонка. Абсолютні струмові виміри показали, що під час проходження зондів струмовою оболонкою загальний струм розряду співпадає зі струмом, що протікає у ній, але в момент особливості його величина усередині R<15см у 2-3 рази менше за повний струм за період усіх пострілів. Спостережені вихрові тороїд альні струми в остаточному газі, який оточує пінч.Проведены исследования токовой оболочки плазменного фокуса филипповского типа с энергетикой 60 кДж и максимальным током 0.9 МА. В эксперименте сравнивались одновременные показания полного тока разряда с пояса Роговского и токов, регистрируемых двумя магнитными зондами внутри приосевой области R < 20 см и R < 15 см. Обнаружено существование вторых и третьих токовых оболочек, следующих за первой, в выстрелах с низким нейтронным выходом. При нормальном выходе существует только одна токовая оболочка. Абсолютные токовые измерения показали, что во время прохождения зондов токовой оболочкой полный ток разряда совпадает с током, текущим в ней, но в момент особенности его значение внутри R<15см в 2-3раза меньше полного тока во всех выстрелах. Обнаружены вихревые тороидальные токи в остаточном газе, окружающем пинч

Energy scales in a stabilized brane world

Brane world gravity looks different for observers on positive and negative tension branes. First we consider the well-known RS1 model with two branes embedded into the AdS_5 space-time and recall the results on the relations between the energy scales for an observer on the negative tension brane, which is supposed to be "our" brane. Then from the point of view of this observer we study energy scales and masses for the radion and graviton excitations in a stabilized brane world model. We argue that there may be several possibilities leading to scales of the order 1-10 TeV or even less for new physics effects on our brane. In particular, an interesting scenario can arise in the case of a "symmetric" brane world with a nontrivial warp factor in the bulk, which however takes equal values on both branes.Comment: 15 pages, corrected typos, enlarged conten

Effective Lagrangians for physical degrees of freedom in the Randall-Sundrum model

We derive the second variation Lagrangian of the Randall-Sundrum model with two branes, study its gauge invariance and diagonalize it in the unitary gauge. We also show that the effective four-dimensional theory looks different on different branes and calculate the observable mass spectra and the couplings of the physical degrees of freedom of 5-dimensional gravity to matter.Comment: 22 pages, LaTeX, typos correcte

Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold

Compton scattering is one of the fundamental interaction processes of light with matter. Already upon its discovery [1] it was described as a billiard-type collision of a photon kicking a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. Then ionization by Compton scattering becomes an intriguing quantum phenomenon. Here we report a kinematically complete experiment on Compton scattering at helium atoms below that threshold. We determine the momentum correlations of the electron, the recoiling ion, and the scattered photon in a coincidence experiment finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7] where similar momentum patterns occur.Comment: 7 pages, 4 figure

Braneworlds in six dimensions: new models with bulk scalars

Six dimensional bulk spacetimes with 3-- and 4--branes are constructed using certain non--conventional bulk scalars as sources. In particular, we investigate the consequences of having the phantom (negative kinetic energy) and the Brans--Dicke scalar in the bulk while obtaining such solutions. We find geometries with 4--branes with a compact on--brane dimension (hybrid compactification) which may be assumed to be small in order to realize a 3--brane world. On the other hand, we also construct, with similar sources, bulk spacetimes where a 3--brane is located at a conical singularity. Furthermore, we investigate the issue of localization of matter fields (scalar, fermion, graviton, vector) on these 3-- and 4--branes and conclude with comments on our six dimensional models.Comment: 24 pages, 1 figure, Replaced to match version published in Class. Quant. Gra

An inhomogeneous toy-model of the quantum gravity with explicitly evolvable observables

An inhomogeneous (1+1)-dimensional model of the quantum gravity is considered. It is found, that this model corresponds to a string propagating against some curved background space. The quantization scheme including the Wheeler-DeWitt equation and the "particle on a sphere" type of the gauge condition is suggested. In the quantization scheme considered, the "problem of time" is solved by building of the quasi-Heisenberg operators acting in a space of solutions of the Wheeler-DeWitt equation and the normalization of the wave function corresponds to the Klein-Gordon type. To analyze the physical consequences of the scheme, a (1+1)-dimensional background space is considered for which a classical solution is found and quantized. The obtained estimations show the way to solution of the cosmological constant problem, which consists in compensation of the zero-point oscillations of the matter fields by the quantum oscillations of the scale factor. Along with such a compensation, a slow global evolution of a background corresponding to an universe expansion exists.Comment: 18 page

Linearized gravity on the Randall-Sundrum two-brane background with curvature terms in the action for the branes

We study gravitational perturbations in the Randall-Sundrum two-brane background with scalar-curvature terms in the action for the branes, allowing for positive as well as negative bulk gravitational constant. In the zero-mode approximation, we derive the linearized gravitational equations, which have the same form as in the original Randall-Sundrum model but with different expressions for the effective physical constants. We develop a generic method for finding tachyonic modes in the theory, which, in the model under consideration, may exist only if the bulk gravitational constant is negative. In this case, if both brane gravitational constants are nonzero, the theory contains one or two tachyonic mass eigenvalues in the gravitational sector. If one of the brane gravitational constants is set to zero, then either a single tachyonic mass eigenvalue is present or tachyonic modes are totally absent depending on the relation between the nonzero brane gravitational constant and brane separation. In the case of negative bulk gravitational constant, the massive gravitational modes have ghost-like character, while the massless gravitational mode is not a ghost in the case where tachyons are absent.Comment: 23 pages, revtex, published versio