International Journal of Modern Physics A

B-meson light-cone distribution amplitudes are discussed in these lectures in the framework of HQET. The evolution equation for the leading-twist distribution amplitude is derived in one-loop approximation. QCD sum rules for distribution amplitudes are discussed.

We discuss ideas and problems regarding classical and quantum gravity, gauge theory of gravity, and space–time transformations between accelerated frames. Both Einstein's theory of gravity and Yang–Mills theory are gauge invariant. The invariance principles are at the very heart of our understanding of the physical world. This paper attempts to survey the development and to reveal problems and limitations of various formulations to gravitational and Yang–Mills fields, and to space–time transformations of accelerated frames. Gravitational force and accelerated frames are two ingredients in Einstein's thought in the period around 1907. Accelerated frames are difficult to define and are not well developed. However, one cannot claim to have a complete understanding of the physical world, if one understands flat space–time physics only from the viewpoint of the special class of inertial frames and ignores the vast class of noninertial frames. The paper highlights three aspects: (1) ideas of gravity as a Yang–Mills field, first discussed by Utiyama; (2) problems of quantum gravity, discussed by Feynman, Dyson and others; (3) space–time properties and the physics of fields and particles in accelerated frames of reference. These unfulfilled aspects of Einstein and Yang–Mills' profound thoughts present a challenge to physicists and mathematicians in the 21st century.

Exact cylindrically symmetric solutions of Einstein–Maxwell equations are presented. They are regular on the axis of symmetry, asymptotically flat and free from curvature singularities. The solutions can be interpreted as nonrotating cosmic strings interacting with gravitational and electromagnetic waves.

In an earlier paper appropriate limiting procedure is discussed in a general way for quantum mechanical energy eigenfunctions (one-dimensional bound states) — a single interpretational postulate leading smoothly to entire compatible classical objective description without facing any contradiction. The method is consistently extended to two- and three-dimensional cases and it is interesting to note that results of earlier study on the classical limit of the radial distribution function of hydrogen atom are easily obtained as special cases of our analysis.

In anticipation of subsequent application to QED and QCD, we consider the case of a model, high temperature, relativistic, scalar field theory. We introduce into the exact, nonperturbative, functional expressions of this "quenched" model, a new Fradkin representation, and extract the infrared/Bloch–Nordsieck/(IR/BN) contributions of every perturbative graph, in order to circumvent the lack of a clear-cut separation of energy scales of previous semiperturbative treatments. Our results are applicable to the absorption of a fast particle which enters a heat bath, as well as to the propagation of a symmetric pulse within the thermal medium due to the appearance of an instantaneous, shockwave-like source acting in the medium. In momentum space, the former case displays a propagator which decays exponentially with increasing time, in addition to a new damping factor independent of time. The latter case displays an exponential growth with time of the symmetric pulse, generating effective and increasing plasmon waves, in competition with damping independent of time. When extended to QCD, qualitative applications could be made to RHIC scattering, in which a fireball appears, expands and is damped away.

Employing the Quark Mass Density- and temperature-dependent model and the Hartle's method, we have studied the slowly rotating strange star with uniform angular velocity. The mass–radius relation, the moment of inertia and the frame dragging for different frequencies are given. We found that we cannot use the strange star to solve the challenges of Stella and Vietri for the horizontal branch oscillations and the moment of inertia I₄₅/(M/M_s)>2.3. Furthermore, we extended the Hartle's method to study the differential rotating strange star and found that the differential rotation is an effective way to get massive strange star.

We discuss the mass splitting between the the top and bottom quarks in a technicolor scenario. The model proposed here contains a left–right electroweak gauge group. An extended technicolor group and mirror fermions are introduced. The top-bottom quark mass splitting turns out to be intimately connected to the breaking of the left–right gauge symmetry. Weak isospin violation occurs within the experimental limits.

This paper is devoted to discuss some of the features of self-similar solutions of the first kind. We consider the cylindrically symmetric solutions with different homotheties. We are interested in evaluating the quantities acceleration, rotation, expansion, shear, shear invariant and expansion rate. These kinematical quantities are discussed both in comoving as well as in noncomoving coordinates (only in radial direction). Finally, we would discuss the singularity feature of these solutions. It is expected that these properties would help in exploring some interesting features of the self-similar solutions.

The hydrodynamic waves of gravity in the galactic interstellar medium generated by a pulsating neutron star are discussed in this paper. It is shown that the frequency of oscillations of interstellar gas–dust matter in this wave is proportional to that for the g-mode in the neutron star bulk. The corresponding periods are of the millisecond duration. The collective oscillations of charged species in the interstellar wave of gravity can produce electromagnetic radiation, and that the only radio waves of this radiation can freely travel through the galactic gas–dust clouds, suggests that this kind of interstellar waves can manifest itself in the radio range of spectra of a neutron star undergoing pulsations triggered by starquake. This inference is in line with the statement that quasiperiodic micropulses with a time scale of a few milliseconds located in the windows of the main pulse train of the radio pulsar spectra owe their origin to pulsations of neutron stars.

The Back-Propagation neural network method is used to identify quark and gluon jets generated by Monte Carlo method. The effects of some factors, such as the architecture of neural network, the input parameters, the training precision and the acceptance cut, on the performance of the neural network are studied in detail. The efficiency and purity of identified quark and gluon jets are calculated for different network architectures. It is found that in order to keep the role of all the input parameters balance, they have to be scaled to the same order of magnitude. Through the study on how the efficiency and purity of the identified quark- and gluon-jets vary with the training precision and acceptance cut, a guidance for how to choose these two parameters is given.

We discuss the pure gauge Schwinger–Dyson equation for the gluon propagator in the Landau gauge within an approximation proposed by Mandelstam many years ago. We show that a dynamical gluon mass arises as a solution. This solution is obtained numerically in the full range of momenta that we have considered without the introduction of any ansatz or asymptotic expression in the infrared region. The vertex function that we use follows a prescription formulated by Cornwall to determine the existence of a dynamical gluon mass in the light cone gauge. The renormalization procedure differs from the one proposed by Mandelstam and allows for the possibility of a dynamical gluon mass. Some of the properties of this solution, such as its dependence on Λ_QCD and its perturbative scaling behavior are also discussed.

We study dynamics of a D3-brane propagating in the vicinity of k coincident NS5 branes. We show that when g_s is small, there exists a regime in which dynamics of the D-brane is governed by Dirac–Born–Infeld action while higher order derivative in the expansion cannot be neglected. This leads to a restriction on how fast scalar field may roll. We analyze the motion of a rolling scalar field in this regime, and extend the analysis to cosmological systems obtained by coupling this type of field theory to four-dimensional gravity. It also leads to some FRW cosmologies, some of which are related to those obtained with tachyon matter.

We investigate D-branes in the Nappi–Witten model. Classically symmetric D-branes are classified by the (twisted) conjugacy classes of the Nappi–Witten group, which specify the geometry of the corresponding D-branes. Quantum description of the D-branes is given by boundary states, and we need one-point functions of closed strings to construct the boundary states. We compute the one-point functions solving conformal bootstrap constraints, and check that the classical limit of the boundary states reproduces the geometry of D-branes.