November 1995 arXiv papers — page 3

Itzhak Bars

The SL(2,R) WZW model, one of the simplest models for strings propagating in curved space time, was believed to be non-unitary in the algebraic treatment involving affine current algebra. It is shown that this was an error that resulted from neglecting a zero mode that must be included to describe the correct physics of non-compact WZW models. In the presenc

Hiroshi Ishikawa

Two-dimensional fermionic string theory is shown to have a structure of topological model, which is isomorphic to a tensor product of two topological ghost systems independent of each other. One of them is identified with $c=1$ bosonic string theory while the other has trivial physical contents. This fact enables us to regard two-dimensional fermionic string

Ambar Ghosal, Asim K. Ray

We demonstrate that the solar and atmospheric neutrino data as well as the recent result of the LSND experiment cannot be satisfied simultaneously with three light neutrinos if we consider the mass degeneracy for two neutrinos in the context of an extended Harvard Model based on the gauge group $SU(2)_{qL}\times {SU(2)}_{lL}\times {U(1)}_Y$ with $S_3\times Z

J. Lopez, D. Nanopoulos

We present a new scenario for gauge coupling unification in flipped SU(5) string models, which identifies the $M_{32}$ scale of SU(3) and SU(2) unification with the empirical $M_{\rm LEP}\sim10^{15-16}$~GeV scale, and the $M_{51}$ scale of SU(5) and U(1) unification with the theoretical $M_{\rm string}\sim5\times10^{17}$~GeV string unification scale. The vac

M. Bertini, M. Giffon, L. Jenkovszky, F. Paccanoni

We discuss some properties of the Pomeron in high energy elastic hadron-hadron and deep inelastic lepton-hadron scattering. A number of issues concerning the nature and the origin of the Pomeron are briefly recalled here. The novelty in this paper resides essentially in its presentation; we strive at discussing all these various issues in the following unify

Adam Szczepaniak, Eric S. Swanson, Chueng-Ryong Ji, Stephen R. Cotanch

A comprehensive, relativistic many-body approach to hadron structure is advanced based on the Coulomb gauge QCD Hamiltonian. Our method incorporates standard many-body techniques which render the approximations amenable to systematic improvement. Using BCS variational methods, dynamic chiral symmetry breaking naturally emerges and both quarks and gluons acqu

Beatriz de Carlos, Marco A. Diaz

Selectrons may be produced in pairs at LEPII if their mass is less than about 100 GeV. Preferably, they decay into the lightest neutralino plus an electron. In a scenario where selectrons are observed at LEPII, we show that: (i) in a first stage where experimental errors are large, the measurement of the total cross section of selectron pair production, the

A. M. Kotzinian, P. J. Mulders

Accounting for transverse momenta of the quarks, a longitudinal quark spin asymmetry exists in a transversely polarized nucleon target. The relevant leading quark distribution $g_{1T}(x,k_T^2)$ can be measured in the semi-inclusive deep-inelastic scattering. The average $k_T^2$ weighted distribution function $g^{(1)}_{1T}$ can be obtained directly from the i

L. Ya. Glozman

New results on baryon structure and spectrum developed in collaboration with Dan Riska [1-4] are reported. The main idea is that beyond the chiral symmetry spontaneous breaking scale light and strange baryons should be considered as systems of three constituent quarks with an effective confining interaction and a chiral interaction that is mediated by the oc

S. Esposito, G. Capone

We study the properties of neutrinos propagating in an isotropic magnetized medium in the two physical approximations of degenerate Fermi gas and classical plasma. The dispersion relation shows that, for peculiar configurations of the magnetic field, neutrinos can propagate freely as in vacuum, also for very large density; this result can be very important i

Juha T. Peltoniemi

It is claimed that radiative corrections maintain the proportionality between the neutrino mass and the neutrino-majoron coupling and never give rise to enhanced decay rates in conventional majoron models. The coupling of a majoron to neutrinos is calculated at one loop level in various models, including the singlet majoron model and the Zee model with a maj

M. -P. Lombardo, J. B. Kogut, D. K. Sinclair

We simulate lattice QCD at non--zero baryon density and zero temperature in the quenched approximation, both in the scaling region and in the infinite coupling limit. We investigate the nature of the forbidden region -- the range of chemical potential where the simulations grow prohibitively expensive, and the results, when available, are puzzling if not unp

M. Goeckeler, R. Horsley, E. -M. Ilgenfritz, H. Perlt

We describe a high statistics quenched QCD calculation of the moments of the polarized deep-inelastic structure functions g_1 and g_2 of the proton and neutron.

L. P. Grishchuk

The genuine quantum gravity effects can already be around us. It is likely that the observed large-angular-scale anisotropies in the microwave background radiation are induced by cosmological perturbations of quantum-mechanical origin. Such perturbations are placed in squeezed vacuum quantum states and, hence, are characterized by large variances of their am

Leszek M. Sokolowski

Among relativistic theories of gravitation the closest ones to general relativity are the scalar-tensor ones and these with Lagrangians being any function f(R) of the curvature scalar. A complete chart of relationships between these theories and general relativity can be delineated. These theories are mathematically (locally) equivalent to general relativity

A. Feinstein, J. Ibáñez, Ruth Lazkoz

We present a new generating algorithm to construct exact non static solutions of the Einstein field equations with two-dimensional inhomogeneity. Infinite dimensional families of $G_1$ inhomogeneous solutions with a self interacting scalar field, or alternatively with perfect fluid, can be constructed using this algorithm. Some families of solutions and the

Sunil D Maharaj, Peter GL Leach, Roy Maartens

The integrability properties of the field equation $L_{xx} = F(x)L^2$ of a spherically symmetric shear--free fluid are investigated. A first integral, subject to an integrability condition on $F(x)$, is found, giving a new class of solutions which contains the solutions of Stephani (1983) and Srivastava (1987) as special cases. The integrability condition on

R. Beig, N. Ó Murchadha

In this article we show that one can construct initial data for the Einstein equations which satisfy the vacuum constraints. This initial data is defined on a manifold with topology $R^3$ with a regular center and is asymptotically flat. Further, this initial data will contain an annular region which is foliated by two-surfaces of topology $S^2$. These two-s

B. L. Altshuler, A. M. Boyarsky, A. Yu. Neronov

The tool of functional averaging over some ``large'' diffeomorphisms is used to describe quantum systems with constraints, in particular quantum cosmology, in the language of quantum Effective Action. Simple toy models demonstrate a supposedly general phenomenon: the presence of a constraint results in ``quantum repel'' from the classical mas

Ruy Exel

Given a group G, we construct, in a canonical way, an inverse semigroup S(G) associated to G. The actions of S(G) are shown to be in one-to-one correspondence with the partial actions of G, both in the case of actions on a set, and that of actions as operators on a Hilbert space. In other words, G and S(G) have the same representation theory. We show that S(

Ji-Hai Xu, Yong Ren, C. S. Ting

YBa$_2$Cu$_3$O$_7$ (YBCO) exhibits a large anisotropy between the $a$ and $b$ axes in the CuO$_2$ planes because of the presence of CuO chains. In order to account for such an anisotropy we develop a Ginzburg-Landau (GL) theory for an anisotropic d-wave superconductor in an external magnetic field, based on an anisotropic effective mass approximation within

Fermin Aldabe

We derive an expression for the correlation function of the random force on a soliton which is consistent with the constraints needed to integrate out the zero modes which appear due to the broken translational symmetry of the soliton solution. It is shown that when the constraint does not commute with the operator which defines the correlation function, i.e

D. Averin, H. Imam

Spectral density of current fluctuations in a short ballistic superconducting quantum point contact is calculated for arbitrary bias voltages $V$. Contrary to a common opinion that the supercurrent flow in Josephson junctions is coherent process with no fluctuations, we find extremely large current noise that is {\em caused} by the supercurrent coherence. An

M. M. Leivo, J. P. Pekola, D. V. Averin

We suggest and demonstrate in experiment that two normal metal /insulator/ superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistances 1.0 and 1.1 k$Ω$ is capable of reaching a temperatur

C. N. Likos, A. Maritan

We present an extension of the previously proposed mean-field renormalization method to model Hamiltonians which are characterized by more than just one type of interaction. The method rests on scaling assumptions about the magnetization of different sublattices of the given lattice and it generates as many flow equations as coupling constants without arbitr

Wayne Hu

These lecture notes form a primer on the theory of cosmic microwave background (CMB) anisotropy formation. With emphasis on conceptual aspects rather than technical issues, we examine the physical foundations of anisotropy evolution in relativistic kinetic and perturbation theory as well as the manifestation of these principles in primary and secondary aniso

Enrico Cappellaro, Massimo Turatto

Using an updated SN list and galaxy parameters from the RC3 catalog, we have revisited two well know biases affecting SN searches. We show that the bias in the central region of galaxies is negligible for galaxies closer than 40 Mpc (H=75), but causes the loss of almost 50% of SNe in the distance range 80-160 Mpc. This bias has a weak dependence on the galax

Zoltan Haiman, Martin Rees, Abraham Loeb

We investigate the formation of molecular hydrogen (H_2) in a primordial H+He gas cloud irradiated by a power-law UV flux. We find that at high densities (>1 cm^{-3}) and low temperatures (<10^4 K), the background radiation enhances the formation of H_2 and results in molecular cooling dominating over photoionization heating. This process could accelerate th

D. Montes, M. J. Fernandez-Figueroa, M. Cornide, E. De Castro

In this work we analyze the behaviour of the excess Ca~{\sc ii} H \& K and H$ε$ emissions in a sample of 73 chromospherically active binary systems (RS$~$CVn and BY$~$Dra classes), of different activity levels and luminosity classes. This sample includes the 53 stars analyzed by Fernández-Figueroa et al. (1994) and the observations of 28 systems described by

Douglas C. Heggie

We first review the reasons for carrying out statistical analysis of results from large numbers of N-body simulations, including a summary of previous work. Then we describe some results about the behaviour of N-body systems which have been acquired by this technique. Finally we concentrate on the problems associated with the scaling of N-body data with N, w

Simon P. Driver, Rogier A. Windhorst, Richard E. Griffiths

We present a complete morphologically classified sample of 144 faint field galaxies from the HST Medium Deep Survey with 20.0 < I <22.0 mag. We compare the global properties of the ellipticals, early and late-type spirals, and find a non-negligible fraction (13/144) of compact blue [(V-I) < 1.0 mag] systems with $r^{1/4}$-profiles. We give the differential g

Boris V. Karpov

Let S be a smooth projective surface, K be the canonical class of S and H be an ample divisor such that H.K<0 . In this paper we prove that for any rigid (Ext^1(F,F)=0) semistable sheaf F in the sense of Mumford--Takemoto stability w.r.t. H there exists an exceptional collection (E_1,...,E_n) of sheaves on S such that F can be constructed from {E_i} by a fin

D. G. Polyakov

We present a microscopic theory of spin-orbit coupling in the integer quantum Hall regime. The spin-orbit scattering length is evaluated in the limit of long-range random potential. The spin-flip rate is shown to be determined by rare fluctuations of anomalously high electric field. A mechanism of strong spin-orbit scattering associated with exchange-induced

Clovis Wotzasek

We study the interacting chiral boson and observe that a naive gauging procedure leaves the covariant chiral constraint incompatible with the field equations. Consistency, therefore, rules out most gauging schemes: in a left chiral scalar, only the coupling with the left chiral currents leads to consistent results, in discordance with current literature.

Oktay K. Pashaev

We show that the Nonlinear Schrödinger Equation and the related Lax pair in 1+1 dimensions can be derived from 2+1 dimensional Chern-Simons Topological Gauge Theory. The spectral parameter, a main object for the Loop algebra structure and the Inverse Spectral Transform, has appear as a homogeneous part (condensate) of the statistical gauge field, connected w

B. Ananthanarayan, P. N. Pandita

We present a detailed discussion of the particle spectrum of the Non-Minimal Supersymmetric Standard Model (NMSSM), containing two Higgs doublets and a singlet, in the limit $\tanβ\simeq m_t/m_b$. This is compared with the corresponding particle spectrum of the Minimal Supersymmetric Standard Model (MSSM). In this limit the singlet vacuum expectation value i

Martin D. Weinberg

I selectively review the various dynamical scenarios that have been explored to date, especially those that illustrate the conundrums. In short, although the existence of asymmetries are convincing enough, the interpretation remains ambiguous. A coherent picture for the Milky Way asymmetries is an obvious lack; each mechanism is considered independently of a

Martin D. Weinberg

This report describes a modification of the orthogonal function Poisson solver for n-body simulations that minimizes relaxation caused by small particle number fluctuations. With the standard algorithm, the noise leading to relaxation can be reduced by making the expansion basis similar to the particle distribution and by carefully choosing the maximum order

Ivar Suisalu, Enn Saar

We study the accumulation of errors in cosmological N-body algorithms that are caused by representing the continuous distribution of matter by massive particles, comparing the PPPM and Adaptive Multigrid codes. We use for this a new measure of two-body relaxation suitable for nonstationary gravitating systems. This measure is based on accumulated deflection

Vladimir S. Strelnitski, Howard A. Smith, Victor O. Ponomarev

The conditions of masing and lasing in the hydrogen recombination lines (HLR) in the disk and outflow of MWC349 are studied. Comparison of the complete set of the observed aphal-lines, with simple models of optically thin spontaneous emission shows that observable HRL masing in this source is limited to the interval of the principal quantum numbers 10-36.

Vladimir S. Strelnitski, Victor O. Ponomarev, Howard A. Smith

The discovery of the first naturally occurring high gain hydrogen recombination line (HRL) maser, in the millimeter and submillimeter spectrum of the emission line star MWC349, requires an expansion of current paradigms about HRLs. In this paper we re-examine in general the physics of non-LTE populations in recombining hydrogen and specify the conditions nec

T. Blum, H. -Th. Elze

The new phenomenon of semiquantum chaos is analyzed in a classically regular double-well oscillator model. Here it arises from a doubling of the number of effectively classical degrees of freedom, which are nonlinearly coupled in a Gaussian variational approximation (TDHF) to full quantum mechanics. The resulting first-order nondissipative autonomous flow sy

S. V. Krasnikov

The problem is discussed of whether a traveller can reach a remote object and return back sooner than a photon would when taken into account that the traveller can partly control the geometry of his world. It is argued that under some reasonable assumptions in globally hyperbolic spacetimes the traveller cannot hasten reaching the destination. Nevertheless,

W. A. Rodrigues,, J. Vaz,

We show that Maxwell equations and Dirac equation (with zero mass term) have both subluminal and superluminal solutions in vacuum. We also discuss the possible fundamental physical consequences of our results.

J. Vaz,, W. A. Rodrigues,

In this paper we formulate Maxwell and Dirac theories as an already unified theory (in the sense of Misner and Wheeler). We introduce Dirac spinors as &#34;Dirac square root&#34; of the Faraday bivector, and use this in order to find a spinorial representation of Maxwell equations. Then we show that under certain circunstances this spinor equation reduces to

Ulf H. Danielsson, Bo Sundborg

We find low energy equivalences between $N=2$ supersymmetric gauge theories with different simple gauge groups with and without matter. We give a construction of equivalences based on subgroups and find all examples with maximal simple subgroups. This is used to solve some theories with exceptional gauge groups $G_2$ and $F_4$. We are also able to solve an $

C. J. Hamer, M. Sheppeard, Zheng Weihong, D. Schutte

The Green&#39;s Function Monte Carlo method of Chin et al is applied to SU(2) Yang-Mills theory in (2+1)D. Accurate measurements are obtained for the ground-state energy and mean plaquette value, and for various Wilson loops. The results are compared with series expansions and coupled cluster estimates, and with the Euclidean Monte Carlo results of Teper. A

A. Ghinculov, J. J. van der Bij

We study the influence of two--loop radiative corrections of enhanced electroweak strength on Higgs production at the LHC. We consider Higgs production by the gluon fusion mechanism, with the subsequent decay of the Higgs boson into a pair of Z bosons, and incorporate the resonance shape corrections up to order $(g^2 \, m_H^2 / m_W^2)^2$. We take into accoun

Atsuhiro Kitazawa, Kiyohide Nomura, Kiyomi Okamoto

The phase transitions between the XY, the dimer and the Haldane phases of the spin-1 bond-alternating XXZ chain are studied by the numerical diagonalization. We determine the phase diagram at $T=0$ and also identify the universality class with the level spectroscopy. We find that exactly on $Δ=0$ there is a Berezinskii-Kosterlitz-Thouless transition line whi

Dieter Hartmann, Ramesh Narayan

The BATSE experiment has now observed more than 1100 gamma-ray bursts. The observed angular distribution is isotropic, while the brightness distribution of bursts shows a reduced number of faint events. These observations favor a cosmological burst origin. Alternatively, very extended Galactic Halo (EGH) models have been considered. In the latter scenario, t

Massimo Bianchi

We review the status of duality symmetries in superstring theories. These discrete symmetries mark the striking differences between theories of pointlike objects and theories of extended objects. They prove to be very helpful in understanding non-perturbative effects in string theories. We will also briefly discuss the strange role played by open strings and

Phung Ho Hai

Bialgebras associated to Yang-Baxter operators satisfying the Hecke equation, are considered. It is shown that they are Koszul algebras. Their Poincare&#39; series are calculated via the Poincare&#39; series of the corresponding quantum spaces.

Matthias Neubert

The current status of the theory and phenomenology of weak decays of hadrons containing a heavy quark is reviewed. Exclusive semileptonic and rare decays of $B$ mesons are discussed, as well as inclusive decay rates, the semileptonic branching ratio of the $B$ meson, and the lifetimes of $b$-flavoured hadrons. Determinations of $α_s$ from $Υ$ spectroscopy ar

Fabio Gavarini

Let $ G^τ$ be a connected simply connected semisimple algebraic group, endowed with generalized Sklyanin-Drinfel&#39;d structure of Poisson group, let $ H^τ$ be its dual Poisson group. By means of quantum double construction and dualization via formal Hopf algebras, we construct new quantum groups $ U_{q,φ}^M(\frak{h}) $ --- dual of $ U_{q,φ}^{M&#39;}(\frak{

Julio Fabris, Mairi Sakellariadou

In the context of Kaluza-Klein theories, we consider a model in which the universe is filled with a perfect fluid described by a barotropic equation of state. An analysis of density perturbations employing the synchronous gauge shows that there are cases where these perturbations have an exponential growth during a de Sitter phase evolution in the external s

Tobias Hurth

We analyze nonabelian massive Higgs-free theories in the causal Epstein-Glaser approach. Recently, there has been renewed interest in these models. In particular we consider the well-known Curci-Ferrari model and the nonabelian Stückelberg models. We explicitly show the reason why the considered models fail to be unitary. In our approach only the asymptotic

N. Dupuis, G. Chitov

We show that the renormalization group (RG) approach to interacting fermions at one-loop order recovers Fermi liquid theory results when the forward scattering zero sound (ZS) and exchange (ZS$&#39;$) channels are both taken into account. The Landau parameters are related to the fixed point value of the ``unphysical&#39;&#39; limit of the forward scattering

Brian P. Dolan

It is shown that the renormalisation group flow in coupling constant space can be interpreted in terms of a dynamical equation for the couplings analogous to viscous fluid flow under the action of a potential. For free scalar field theory the flow is geodesic in two dimensions, while for $D \neq 2$ it is only geodesic in certain limits, e.g. for vanishing ex

Hans van Leeuwen, Hans Maassen

We consider two independent q-Gaussian random variables X and Y and a function f chosen in such a way that f(X) and X have the same distribution. For 0 < q < 1 we find that at least the fourth moments of X + Y and f(X) + Y are different. We conclude that no q-deformed convolution product can exist for functions of independent q-Gaussian random variables.

E. Elizalde, M. Kawamura, S. Nojiri, S. D. Odintsov

The static potential is investigated in string and membrane theories coupled to $U(1)$ gauge fields (specifically, external magnetic fields) and with antisymmetric tensor fields. The explicit dependence of the potential on the shape of the extended objects is obtained, including a careful calculation of the quantum effects. Noting the features which are comm

Andrei P. Kirilyuk

The physical consequences of the analysis performed in Parts I-IV are outlined within a scheme of the complete quantum (wave) mechanics called quantum field mechanics and completing the original ideas of Louis de Broglie by the dynamic complexity concept. The total picture includes the formally complete description at the level of the "average" wave function

Robert Carroll

We survey some topics involving the Whitham equations, concentrating on the role of the product of the wave function and its adjoint in averaging and in producing Cauchy kernels and differentials on Riemann surfaces. There are also some new results.

Uwe Grimm

The definition of a dilute braid-monoid algebra is briefly reviewed. The construction of solvable vertex and interaction-round-a-face models built on representations of the dilute Temperley-Lieb and Birman-Wenzl-Murakami algebras is discussed.

R. J. Furnstahl, Brian D. Serot, Hua-Bin Tang

An analysis of nuclear properties based on a relativistic energy functional containing Dirac nucleons and classical scalar and vector meson fields is discussed. Density functional theory implies that this energy functional can include many-body effects that go beyond the simple Hartree approximation. Using basic ideas from effective field theory, a systemati

Gabor Fejes Tóth, Greg Kuperberg, Włodzimierz Kuperberg

We introduce and study certain notions which might serve as substitutes for maximum density packings and minimum density coverings. A body is a compact connected set which is the closure of its interior. A packing $\cal P$ with congruent replicas of a body $K$ is $n$-saturated if no $n-1$ members of it can be replaced with $n$ replicas of $K$, and it is comp

G. Lambiase, V. V. Nesterenko

The quark mass dependence of the energy spectrum in the Nambu--Goto string with point--like masses (quarks) at its ends is analyzed. To this end, linearized equations of motion and boundary conditions in this model are considered. It is shown that for sufficiently large quark masses, the first excited state in string spectrum may be arbitrary close to the gr

Uwe Grimm, Bernard Nienhuis

The dilute A_3 model is a solvable IRF (interaction-round-a-face) model with three local states and adjacency conditions encoded by the Dynkin diagram of the Lie algebra A_3. It can be regarded as a solvable version of a critical Ising model in a magnetic field. One therefore expects the scaling limit to be governed by Zamolodchikov&#39;s integrable perturba

A. L. Carey, M. K. Murray, B. L. Wang

The notion of a higher bundle gerbe is introduced to give a geometric realization of the higher degree integral cohomology of certain manifolds. We consider examples using the infinite dimensional spaces arising in gauge theories.

G. Wilk, Z. Wlodarczyk

A number of seemingly {\it exotic} phenomena seen in the highest cosmic-ray experiments are briefly discussed. We argue that they indicate existence of non-statistical fluctuations and strong correlations in the fragmentation region of multiparticle production processes unaccessible to the present accelerators.

Lina Paria, M. G. Mustafa, Afsar Abbas

We obtain a heavy glueball (much heavier than the ones studied by others which usually are in the range of 1-2 GeV) in a bag model calculation with exact discrete single particle states of gluons at finite temperature. This heavy glueball, within the cosmological context, is what Abbas has recently predicted (hep-ph/9504430).

Gerhard Ecker

After a brief introduction to chiral perturbation theory, the effective field theory of the standard model at low energies, two recent applications are reviewed: elastic pion-pion scattering to two-loop accuracy and the complete renormalized pion-nucleon Lagrangian to $O(p^3)$ in the chiral expansion.

Paul Hoyer

I briefly review our understanding of the nuclear target dependence of charm and charmonium production, in view of charm physics at Elfe.

Karol Kolodziej, Arnd Leike, Reinhold Rueckl

We discuss two-photon and hadronic production of $B_c$ mesons in nonrelativistic bound state approximation and to lowest order in the coupling constants $α$ and $α_s$. It is shown that in photon-photon collisions, heavy quark fragmentation is dominated by recombination of $\bar b$ and $c$ quarks up to the highest accessible transverse momenta. In contrast, i

S. M. H. Wong

We argue that in QCD, the Debye mass requires not only a mathematical definition but also a physical one and temporal axial gauge could provide for a physical screening potential for this purpose. Unfortunately, this gauge is spoiled by problem of energy conservation rather than the well known divergence due to the double pole in the longitudinal propagator.

Ulrich Nierste, Kurt Riesselmann

We discuss different aspects of the Higgs self-interaction in the MS-bar and the on-mass-shell (OMS) scheme. The running coupling λ(μ) is investigated in great detail. The three-loop coefficient of the β-function in the OMS scheme is derived, and the three-loop running coupling is calculated. The breakdown of perturbation theory for large Higgs masses M_H is

Felix M. Lev

Nuclear deep inelastic scattering is considered in the framework of a model in which the current operator explicitly satisfies Poincare invariance and current conservation. The results considerably differ from the standard ones at small values of the Bjorken variable $x$. In particular, it is impossible to extract the neutron structure functions from the deu

M. Klasen, G. Kramer

We have calculated inclusive two-jet cross sections in next-to-leading order QCD for direct photoproduction in low $Q^2$ $ep$ collisions at HERA. Infrared and collinear singularities in real and virtual contributions are cancelled with the phase space slicing method. Analytical formulas for the different contributions giving the dependence on the slicing par

Pieter Maris, Qing Wang

The fermion four-point functions and condensates as the chiral symmetry order parameters are calculated analytically in U(1) gauge theory in the massless phase. It is shown that in leading order of the loop expansion of the effective action, there is a critical coupling for the nonperturbative parity-invariant chirality-changing four-fermion functions; this

A. Feinstein, J. Ibáñez, P. Labraga

Some exact solutions for the Einstein field equations corresponding to inhomogeneous $G_2$ cosmologies with an exponential-potential scalar field which generalize solutions obtained previously are considered. Several particular cases are studied and the properties related to generalized inflation and asymptotic behaviour of the models are discussed.

A. Feinstein, M. A. Pérez Sebastián

The quantization of a real massless scalar field in a spacetime produced in a collision of two electromagnetic plane waves with constant wave fronts is considered. The background geometry in the interaction region, the Bell-Szekeres solution, is locally isometric to the conformally flat Bertotti-Robinson universe filled with a uniform electric field. It is s

Ulf Nilsson, Claes Uggla

Einstein&#39;s field equations for spatially self-similar locally rotationally symmetric perfect fluid models are investigated. The field equations are rewritten as a first order system of autonomous ordinary differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system of differential equations i

Akhil Ranjan, G. Santhanam

Antonio Ros gave a lower bound for the first eigenvalue $λ_1$ of $Δ$ of a $P$-manifold $(M, g)$ in terms of the lower bound on the Ricci curvature $Ric_M$ and asked what happened when this lower bound was achieved. In this paper we look in to this question and show that there are strong implications on the geometry and topology of the underlying manifold. In

T. Senthil, Satya N. Majumdar

We study zero temperature phase transitions in two classes of random quantum systems -the $q$-state quantum Potts and clock models. For models with purely ferromagnetic interactions in one dimension, we show that for strong randomness there is a second order transition with critical properties that can be determined exactly by use of an RG procedure. Somewha

C. Bruder, Rosario Fazio, Herbert Schoeller

We investigate Aharonov-Bohm oscillations of the current through a strongly correlated quantum dot embedded in an arbitrary scattering geometry. Resonant-tunneling processes lead to a flux-dependent renormalization of the dot level. As a consequence we obtain a fine structure of the current oscillations which is controlled by quantum fluctuations. Strong Cou

A. M. Saitta, F. Buda, G. Fiumara, P. V. Giaquinta

We analyze the influence of spatial orientation on the optical response of hydrogenated silicon quantum wires. The results are relevant for the interpretation of the optical properties of light emitting porous silicon. We study (111)-oriented wires and compare the present results with those previously obtained within the same theoretical framework for (001)-

A. Lakshminarayan, M. S. Santhanam, V. B. Sheorey

We study the local scaling properties associated with straight line periodic orbits in homogeneous Hamiltonian systems, whose stability undergoes repeated oscillations as a function of one parameter. We give strong evidence of local scaling of the Poincaré section with exponents depending simply on the degree of homogeneity of the potential.

Arturo Serna, Jean-Michel Alimi, Jean-Pierre Chieze

We present and test a general-purpose code, called PPASPH, for evolving self-gravitating fluids in astrophysics, both with and without a collisionless component. In PPASPH, hydrodynamical properties are computed by using the SPH (Smoothed Particle Hydrodynamics) method while, unlike most previous implementations of SPH, gravitational forces are computed by a

Douglas C. Heggie, Piet Hut

We first review reasons why dark matter is an interesting issue in connection with star clusters. Next we consider to what extent the presence of dark matter is consistent with their dynamics and structure. We review various model-dependent and model-independent methods which have been applied to two well studied clusters, NGC 6397 and 47 Tuc. We suggest tha

W. D. Vacca, B. Leibundgut

In order to investigate non-uniformity in the luminosity evolution of Type Ia supernovae, we fit the lightcurves with a multi-parameter empirical model. The model provides a quantitative method of analyzing the lightcurves of Type I supernovae and a convenient and continuous representation of the photometric data. Using photometry of the well-observed event

M. Villar-Martin, L. Binette

We show that the study of the Calcium depletion is a valid an highly sensitive method for investigating the chemical and physical history of the very extended ionized nebulae seen around radio galaxies (EELR), massive ellipticals and `cooling flow&#39; galaxies. By observing the near IR spectrum of nebular regions characterized by low excitation emission lin

J. Perez, M. Lachieze-Rey

We present a global approach of non-dissipative physics. Based on symplectic mechanics this technique allows us to obtain the solution of a very large class of problems in terms of a Taylor expand. We apply this method to the problem of gravitational instability and we obtain a general expression of the gravitational potential, solution of the Vlasov- Poisso

Russell W. Strickland, David N. Schramm

If the hot, X-ray emitting gas in rich clusters forms a fair sample of the universe (as in Cold Dark Matter (CDM) models), and the universe is at the critical density, $Ω_T = 1$, then the data appears to imply a baryon fraction, $Ω_{b,x}$ ($Ω_{b,x}\equiv Ω_b$ derived from X-ray cluster data), larger than that predicted by Big Bang Nucleosynthesis (BBN). Whil

Sergej A. Kuleshov

The paper consists of three parts. In the first of them different kinds stability are discussed. In particular, the stability concept with respect to nef divisor is introduced. A structure of rigid and superrigid vector bundles on smooth projective surfaces with nef anticanonical class is studied in the second part. We prove that any superrigid bundle has a

Yujiro Kawamata

We obtain a formula which relates the log canonical divisor of the ambient space with that of a subvariety of codimension 2 by using Knudsen&#39;s moduli space of pointed stable curves of genus 0.

Andrei P. Kirilyuk

The concept of fundamental dynamic uncertainty (multivaluedness) developed in Parts I-III of this work and used to establish the consistent understanding of genuine chaos in Hamiltonian systems provides also causal description of the quantum measurement process. The modified Schroedinger formalism involving multivalued effective dynamical functions reveals t

Andrei P. Kirilyuk

The universal dynamic uncertainty, discovered in Parts I and II of this series of papers for the case of Hamiltonian quantum systems, is further specified to reveal the hierarchical structure of levels of dynamically redundant 'realisations' which takes the form of the intrinsically probabilistic 'fundamental dynamical fractal' of a problem and determines fr

T. Csorgo, B. Lorstad

Bose-Einstein correlations and invariant momentum distributions are analyzed for longitudinally expanding finite systems, like jets in elementary particle collisions or systems created in high energy heavy ion reactions. Cross-term generating hyperbolic mixing angle is introduced for HBT. Temporal or spatial temperature gradients are shown to contribute to t

Andrei P. Kirilyuk

The intrinsic multivaluedness of interaction process, revealed in Part I of this series of papers, is interpreted as the origin of the true dynamical (in particular, quantum) chaos. The latter is causally deduced as unceasing series of transitions, dynamically probabilistic by their origin, between the equally real, but incompatible 'realisations' (modes of

J. A. Coarasa, Ricardo A. Jimenez, Joan Sola

We analyze the correlation of QCD one-loop effects on the partial widths of the three neutral Higgs bosons of the MSSM decaying into quark-antiquark pairs. The SUSY-QCD effects turn out to be comparable or even larger than the standard QCD effects and are slowly decoupling in a wide window of the parameter space. Our study is aimed at elucidating the possibl

Andrei P. Kirilyuk

Two major deviations from causality in the existing formulations of quantum mechanics, related respectively to quantum chaos and indeterminate wave reduction, are eliminated within the new, universal concept of dynamic complexity. The analysis involves a new paradigm for description of a system with interaction, the principle of dynamic multivaluedness (redu