Showing papers in "Modern Physics Letters A in 2004"
TL;DR: In this article, the authors analyze the cosmological dynamics of phantom fields in a variety of potentials unbounded from above and demonstrate that the nature of future evolution depends upon the steepness of the phantom potential and discuss the fate of the universe accordingly.
Abstract: In this paper we analyze the cosmological dynamics of phantom field in a variety of potentials unbounded from above. We demonstrate that the nature of future evolution generically depends upon the steepness of the phantom potential and discuss the fate of the universe accordingly.
255 citations
TL;DR: In this paper, it was shown that a causal set's discreteness is locally Lorentz invariant, contrary to what is often stated, a fundamental spacetime discreteness need not contradict Lorentzi invariance.
Abstract: Contrary to what is often stated, a fundamental spacetime discreteness need not contradict Lorentz invariance. A causal set's discreteness is in fact locally Lorentz invariant, and we recall the re...
191 citations
TL;DR: In this paper, a systematic procedure to study one-dimensional Schrodinger equation with a position-dependent effective mass (PDEM) in the kinetic energy operator is explored, and a unified approach to many exact results known in the literature, as well as to a lot of new ones is provided.
Abstract: A systematic procedure to study one-dimensional Schrodinger equation with a position-dependent effective mass (PDEM) in the kinetic energy operator is explored. The conventional free-particle problem reveals a new and interesting situation in that, in the presence of a mass background, formation of bound states is signalled. We also discuss coordinate-transformed, constant-mass Schrodinger equation, its matching with the PDEM form and the consequent decoupling of the ambiguity parameters. This provides a unified approach to many exact results known in the literature, as well as to a lot of new ones.
146 citations
TL;DR: In this paper, the authors studied the properties of matrix models with soft confining potentials and showed that these models are equivalent to matrix models that appear in Chern-Simons theory.
Abstract: We study the properties of matrix models with soft confining potentials. Their precise mathematical characterization is that their weight function is not determined by its moments. We mainly rely on simple considerations based on orthogonal polynomials and the moment problem. In addition, some of these models are equivalent, by a simple mapping, to matrix models that appear in Chern–Simons theory. The models can be solved with q deformed orthogonal polynomials (Stieltjes–Wigert polynomials), and the deformation parameter turns out to be the usual q parameter in Chern–Simons theory. In this way, we give a matrix model computation of the Chern–Simons partition function on S3 and show that there are infinitely many matrix models with this partition function.
143 citations
TL;DR: In this article, it is shown that Friedmann and k-field equations may be analytically integrated for arbitrary kfield potentials during evolution with a constant baryotropic index.
Abstract: We study spatially flat isotropic universes driven by k-essence. It is shown that Friedmann and k-field equations may be analytically integrated for arbitrary k-field potentials during evolution with a constant baryotropic index. It follows that there is an infinite number of dynamically different k-theories with equivalent kinematics of the gravitational field. We show that there is a large "window" of stable solutions, and that the dust-like behavior separates stable from unstable expansion. Restricting to the family of power law solutions, it is argued that the linear scalar field model, with constant function F, is isomorphic to a model with divergent speed of sound and this makes them less suitable for cosmological modeling than the nonlinear k-field solutions we find in this paper.
128 citations
TL;DR: In this paper, a specific conjecture involving quantum open string field theory was proposed to explain the decay of unstable D-branes in string theory, and the recent results in two-dimensional string theory are in exact accordance with this conjecture.
Abstract: Recent investigations involving the decay of unstable D-branes in string theory suggest that the tree level open string theory which describes the dynamics of the D-brane already knows about the closed string states produced in the decay of the brane. We propose a specific conjecture involving quantum open string field theory to explain this classical result, and show that the recent results in two-dimensional string theory are in exact accordance with this conjecture.
121 citations
TL;DR: In this paper, it is shown that such models where the action quickly grows with the decrease of the curvature define the FRW universe with the minimal curvature, and it is demonstrated that quantum effects of conformal fields may strongly suppress the instabilities discovered in modified gravity.
Abstract: We discuss the modified gravity which may produce the current cosmic acceleration of the universe and eliminate the need for dark energy. It is shown that such models where the action quickly grows with the decrease of the curvature define the FRW universe with the minimal curvature. Infinite time is required to reach the minimal curvature during the universe evolution. It is demonstrated that quantum effects of conformal fields may strongly suppress the instabilities discovered in modified gravity. We also briefly speculate on the modification of gravity combined with the presence of the cosmological constant dark energy.
117 citations
TL;DR: By means of unitarized Chiral Perturbation theory, it is possible to obtain a remarkable description of meson-meson scattering amplitudes up to 12 GeV and generate poles associated to scalar and vector resonances as mentioned in this paper.
Abstract: By means of unitarized Chiral Perturbation Theory it is possible to obtain a remarkable description of meson-meson scattering amplitudes up to 12 GeV, and generate poles associated to scalar and vector resonances Since Chiral Perturbation Theory is the QCD low energy effective theory, it is then possible to study its large N_c limit where q q states are easily identified The vectors thus generated follow closely a q q behavior, whereas the light scalar poles follow the large-N-c behavior expected for a dominant tetraquark or two-meson structure
96 citations
TL;DR: In this article, the authors discuss big rip singularities occurring in typical phantom models by violation of the weak energy condition and compare them with future late-time singularities arising in models where the scale factor ends in a constant value and there is no violation of strong energy condition.
Abstract: Here we discuss big rip singularities occurring in typical phantom models by violation of the weak energy condition. After that, we compare them with future late-time singularities arising in models where the scale factor ends in a constant value and there is no violation of the strong energy condition. In phantom models the equation of state is well defined along the whole evolution, even at the big rip. However, both the pressure and the energy density of the phantom field diverge. In contrast, in the second kind of model the equation of state is not defined at the big rip because the pressure bursts at a finite value of the energy density.
88 citations
TL;DR: Based on some important properties of dS space, this paper presented a Beltrami model BA that may shed light on the observable puzzle of DS space and the paradox between the special relativity principle and cosmological principle.
Abstract: Based on some important properties of dS space, we present a Beltrami model BA that may shed light on the observable puzzle of dS space and the paradox between the special relativity principle and cosmological principle. In BA, there are inertial-type coordinates and inertial-type observers. Thus, the classical observables can be defined for test particles and light signals. In addition, by choosing the definition of simultaneity the Beltrami metric is transformed to the Robertson-Walker-like metric. It is of positive spatial curvature of order A. This has already been shown by the CMB power spectrum from WMAP and should be further confirmed by its data in large scale.
77 citations
TL;DR: In this paper, the authors discuss gauge/string correspondence based on the non-critical strings and present several remarkable sigma models with the AdS target spaces, which have kappa symmetry and are completely integrable.
Abstract: In this article we discuss gauge/string correspondence based on the non-critical strings. With this goal we present several remarkable sigma models with the AdS target spaces. The models have kappa symmetry and are completely integrable. The radius of the AdS space is fixed and thus they describe isolated conformal fixed points of gauge theories in various dimensions. This work is dedicated to the memory of Ian Kogan.
TL;DR: In this article, the status of recently observed positive parity charmed resonances, both in the nonstrange and strange sectors, is reviewed, and the experimental findings, main theoretical analyses and the open problems are described.
Abstract: We review the status of recently observed positive parity charmed resonances, both in the non-strange and strange sectors. We describe the experimental findings, the main theoretical analyses and the open problems deserving further investigations.
TL;DR: In this paper, the authors obtained exactly bound states of the generalization of the Woods-Saxon potential with the negative energy levels based on the analytic approach using supersymmetry in quantum mechanics.
Abstract: Using the associated Jacobi differential equation, we obtain exactly bound states of the generalization of Woods–Saxon potential with the negative energy levels based on the analytic approach. According to the supersymmetry approaches in quantum mechanics, we show that these bound states by four pairs of the first-order differential operators, represent four types of the laddering equations. Two types of these supersymmetry structures, suggest the derivation of algebraic solutions by two different approaches for the bound states.
TL;DR: In this article, the status of Planck scale physics in these effective models is reviewed and a review of the current state of the art is given, with a focus on the effects of quantum gravity effects at the lower planck scale.
Abstract: Planck scale physics represents a future challenge, located between particle physics and general relativity. The Planck scale marks a threshold beyond which the old description of spacetime breaks down and conceptually new phenomena must appear. Little is known about the fundamental theory valid at Planckian energies, except that it necessarily seems to imply the occurrence of a minimal length scale, providing a natural ultraviolet cutoff and a limit to the possible resolution of spacetime. Motivated by String Theory, the models of large extra dimensions lower the Planck scale to values soon accessible. These models predict a vast number of quantum gravity effects at the lowered Planck scale, among them the production of TeV-mass black holes and gravitons. Within the extra dimensional scenario, the minimal length also comes into the reach of experiment and sets a fundamental limit to short distance physics. We review the status of Planck scale physics in these effective models.
TL;DR: In this article, the Moller's energy-momentum complex is employed to compute the energy and momentum distributions of a radiating charged particle in a generalization of Bonnor and Vaidya spacetime.
Abstract: The effective gravitational mass as well as the energy and momentum distributions of a radiating charged particle in Einstein's universe are evaluated. The Moller's energy–momentum complex is employed for this computation. The spacetime under study is a generalization of Bonnor and Vaidya spacetime in the sense that the metric is described in the cosmological background of Einstein's universe in lieu of the flat background. Several spacetimes are limiting cases of the one considered here. In particular for the Reissner–Nordstrom black hole background, our results are exactly the same as those derived by Cohen and Gautreau using Whittaker's theorem and by Cohen and de Felice using Komar's mass. Furthermore, the power output for the spacetime under consideration is obtained.
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TL;DR: The cosmological constant combined with Planck's constant and the speed of light implies a quantum of mass of approximately 2×10-65g as mentioned in this paper, which is the largest known quantum mass.
Abstract: The cosmological constant combined with Planck's constant and the speed of light implies a quantum of mass of approximately 2×10-65g. This follows either from a generic dimensional analysis, or from a specific analysis where the cosmological constant appears in 4D spacetime as the result of a dimensional reduction from higher-dimensional relativity (such as 5D induced-matter and membrane theory). In the latter type of theory, all the particles in the universe can be in higher-dimensional contact.
TL;DR: In this paper, the authors review the multiverse concept and the criticisms that have been advanced against it on both scientific and philosophical grounds, including the anthropic principle and the so-called observer selection effect.
Abstract: Recent advances in string theory and inflationary cosmology have led to a surge of interest in the possible existence of an ensemble of cosmic regions, or "universes", among the members of which key physical parameters, such as the masses of elementary particles and the coupling constants, might assume different values The observed values in our cosmic region are then attributed to an observer selection effect (the so-called anthropic principle) The assemblage of universes has been dubbed "the multiverse" In this paper we review the multiverse concept and the criticisms that have been advanced against it on both scientific and philosophical grounds
TL;DR: In this paper, the authors show that the probability for a system with energy E to tunnel across the horizon is P(E)∝exp[-(2π/κ)E) where κ is the surface gravity of the horizon.
Abstract: In any spacetime, it is possible to have a family of observers following a congruence of timelike curves such that they do not have access to part of the spacetime. This lack of information suggests associating a (congruence dependent) notion of entropy with the horizon that blocks the information from these observers. While the blockage of information is absolute in classical physics, quantum mechanics will allow tunnelling across the horizon. This process can be analyzed in a simple, yet general, manner and we show that the probability for a system with energy E to tunnel across the horizon is P(E)∝exp[-(2π/κ)E) where κ is the surface gravity of the horizon. If the surface gravity changes due to the leakage of energy through the horizon, then one can associate an entropy S(M) with the horizon where dS=[2π/κ(M)]dM and M is the active gravitational mass of the system. The implications are discussed.
TL;DR: In this article, the basic ideas of k(t)-factorization and CCFM parton evolution are discussed and the unintegrated gluon densities, obtained from CCFM fits to the proton structure function data at HERA, are used to predict hadronic final state cross-sections like jet production, but also comparisons with recent measurements of heavy quark production at the Tevatron are presented.
Abstract: The basic ideas of k(t)-factorization and CCFM parton evolution is discussed. The unintegrated gluon densities, obtained from CCFM fits to the proton structure function data at HERA are used to predict hadronic final state cross-sections like jet production at HERA, but also comparisons with recent measurements of heavy quark production at the Tevatron are presented. Finally, the k(t)-factorization approach is applied to Higgs production at high energy hadron-hadron colliders and the transverse momentum spectrum of Higgs production at the LHC is calculated.
TL;DR: In this article, an SU(2)L×U(1)Y model with the same particle content as SM and discrete reflection symmetry between second and third generations of leptons gives rise to charged lepton and neutrino mass matrices which can accommodate the present solar, atmospheric, WMAP neutrinos experimental results.
Abstract: We demonstrate that an SU(2)L×U(1)Y model with the same particle content as Standard Model (SM) and discrete reflection symmetry between second and third generations of leptons gives rise to charged lepton and neutrino mass matrices which can accommodate the present solar, atmospheric, WMAP neutrino experimental results. The model predicts the value of |U13| which could be tested in neutrino factories and the effective Majorana neutrino mass which is at the lower end of the present experimental value. Neutrino masses are generated through dim=5 operators and the scale of which are constrained by the value of . If, in future neutrinoless double beta decay experiments namely, MOON, EXO, GENIUS shift the lower bound on by one order, the present model will fail to accommodate the solar neutrino mixing angle due to LMA solution.
TL;DR: A brief review of the current theoretical knowledge in supersymmetry on the lattice can be found in this article, with special emphasis on recent results in the framework of N=1 supersymmetric Yang-Mills theory, Wess-Zumino model and Yang-mills theory with extended supersymmetries.
Abstract: In this brief review, we summarize the current theoretical knowledge in supersymmetry on the lattice, with special emphasis on recent results in the framework of N=1 supersymmetric Yang–Mills theory, Wess–Zumino model and Yang–Mills theory with extended supersymmetries.
TL;DR: In this paper, the T6/(ℤ4×Ω2×Ωℛ) case is discussed in detail and other orbifolds including fractional D6-branes are treated briefly.
Abstract: D6-branes intersecting at angles allow for phenomenologically appealing constructions of four-dimensional string theory vacua. While it is straightforward to obtain non-supersymmetric realizations of the standard model, supersymmetric and stable models with three generations and no exotic chiral matter require more involved orbifold constructions. The T6/(ℤ4×ℤ2×Ωℛ) case is discussed in detail. Other orbifolds including fractional D6-branes are treated briefly.
TL;DR: In this paper, the stationary phase method is applied to diusion by a potential barrier for an incoming wave packet with energies greater than the height of the barrier and the correct solution is the creation of multiple peaks as a consequence of multiple reections.
Abstract: The stationary phase method is applied to diusion by a potential barrier for an incoming wave packet with energies greater than the height of the barrier. It is observed that a direct application leads to paradoxical results. The correct solution, conrmed by numerical calculations is the creation of multiple peaks as a consequence of multiple reections. Lessons concerning the use of the stationary phase method are drawn.
TL;DR: In this article, the bound state wave functions for a wide class of exactly solvable potentials are found by utilizing the quantum Hamilton-Jacobi formalism of Leacock and Padgett.
Abstract: The bound state wave functions for a wide class of exactly solvable potentials are found by utilizing the quantum Hamilton–Jacobi formalism of Leacock and Padgett. It is shown that, exploiting the singularity structure of the quantum momentum function, until now used only for obtaining the bound state energies, one can straightforwardly find both the eigenvalues and the corresponding eigenfunctions. After demonstrating the working of this approach through a few solvable examples, we consider Hamiltonians, which exhibit broken and unbroken phases of supersymmetry. The natural emergence of the eigenspectra and the wave functions, in both unbroken and the algebraically nontrivial broken phase, demonstrates the utility of this formalism.
TL;DR: The high parton density regime of the quantum chromodynamics (QCD), where the physics of parton saturation is expected to dominate, is briefly discussed in this article, mainly focusing on possible signatures of the nonlinear QCD dynamics in the heavy quark production in electron-proton/nucleus collisions.
Abstract: The high parton density regime of the quantum chromodynamics (QCD), where the physics of parton saturation is expected to be dominant, is briefly discussed. Some phenomenological aspects of saturation are described, mainly focusing on possible signatures of the nonlinear QCD dynamics in the heavy quark production in electron–proton/nucleus collisions. Implications of these effects in the heavy quark production in ultraperipheral heavy-ion collisions are also presented.
TL;DR: In this article, a new symmetry-preserving loop regularization method is proposed, which can be applied to both underlying and effective quantum field theories including gauge, chiral, supersymmetric and gravitational ones as the new method does not modify either the Lagrangian formalism or the spacetime dimension of original theory.
Abstract: A new symmetry-preserving loop regularization method proposed in Ref. 1 is further investigated. It is found that its prescription can be understood by introducing a regulating distribution function to the proper-time formalism of irreducible loop integrals. The method simulates in many interesting features to the momentum cutoff, Pauli-Villars and dimensional regularization. The loop regularization method is also simple and general for the practical calculations to higher loop graphs and can be applied to both underlying and effective quantum field theories including gauge, chiral, supersymmetric and gravitational ones as the new method does not modify either the Lagrangian formalism or the spacetime dimension of original theory. The appearance of characteristic energy scale M-c and sliding energy scale mu(s) offers a systematic way for studying the renormalization-group evolution of gauge theories in the spirit of Wilson-Kadanoff and for exploring important effects of higher dimensional interaction terms in the infrared regime.
TL;DR: In this paper, a generalization of the thermodynamic uncertainty relations is proposed, by introducing an additional term proportional to the interior energy into the standard uncertainty relation that leads to existence of the lower limit of inverse temperature.
Abstract: A generalization of the thermodynamic uncertainty relations is proposed. It is done by introducing an additional term proportional to the interior energy into the standard thermodynamic uncertainty relation that leads to existence of the lower limit of inverse temperature. In our opinion the approach proposed may lead to the proofs of these relations. To this end, the statistical mechanics deformation at Planck scale. The statistical mechanics deformation is constructed by analogy to the earlier quantum mechanical results. As previously, the primary object is a density matrix, but now the statistical one. The obtained deformed object is referred to as a statistical density pro-matrix. This object is explicitly described, and it is demonstrated that there is a complete analogy in the construction and properties of quantum mechanics and statistical density matrices at Planck scale (i.e. density pro-matrices). It is shown that an ordinary statistical density matrix occurs in the low-temperature limit at temperatures much lower than the Planck's. The associated deformation of a canonical Gibbs distribution is given explicitly.
TL;DR: In this paper, an anti-de-Sitter universe with quantum CFT with classical phantom matter and perfect fluid was considered and the influence exerted by quantum effects and phantom matter on the AdS space was discussed.
Abstract: We consider an anti de Sitter universe filled by quantum CFT with classical phantom matter and perfect fluid. The model represents the combination of a trace-anomaly annihilated and a phantom driven anti de Sitter universes. The influence exerted by the quantum effects and phantom matter on the AdS space is discussed. Different energy conditions in this type of universe are investigated and compared with those for the corresponding model in a de Sitter universe.
TL;DR: In this article, the structural stability of tachyonic inflation against changes in the shape of the potential was studied. And they found that the models are rigid in the sense that the attractor solutions never change as long as the conditions for inflation are met.
Abstract: We study the structural stability of tachyonic inflation against changes in the shape of the potential. Following Lidsey,10 the concepts of rigidity and fragility are defined through a condition on the functional form of the Hubble factor. We find that the models are rigid in the sense that the attractor solutions never change as long as the conditions for inflation are met.
TL;DR: In this paper, the authors propose to resolve the controversy regarding the stability of the monopole condensation in QCD by calculating the imaginary part of the one-loop effective action perturbatively.
Abstract: We propose to resolve the controversy regarding the stability of the monopole condensation in QCD by calculating the imaginary part of the one-loop effective action perturbatively. We calculate the imaginary part perturbatively to the order g2 with two different methods, with Feynman diagram and with Schwinger's method. Our result shows that with the magnetic background the effective action has no imaginary part, but with the electric background it acquires a negative imaginary part. This strongly indicates a stable monopole condensation in QCD.