International Journal of Modern Physics A

The discovery of numerous new charmonium-like structures since 2003 have revitalized interest in exotic meson spectroscopy. These structures do not fit easily into the conventional charmonium model, and proposals like four-quark states, hybrids and rescattering effects have been suggested as explanations. Since 2009, several new structures were reported in the J/ψϕ mass spectrum with the following characteristics: they are the first ones reported decaying into two heavy mesons which contain both a pair and a pair; and their masses are well beyond the open charm pair threshold. Conventional states with a mass beyond the J/ψϕ threshold are not expected to decay into this channel and the width is expected to be large, thus they are good candidates for exotic mesons. The focus of this paper is to review the recent developments on the structures in the J/ψϕ mass spectrum from CDF, Belle and LHCb.

An experimental review of the current status of the top quark physics program at hadron colliders is presented. Since the discovery of the top quark at the Fermilab Tevatron collider in 1995, its production and the decay have been studied with an extraordinary level of sophistication both at the Tevatron and at the Large Hadron Collider. The top quark is the heaviest known elementary particle, with possible unique connections to the mechanism of electroweak symmetry breaking.

In this paper, we study Einstein gravity with a minimally coupled scalar field accompanied with a potential, assuming an O(4) symmetric metric ansatz. We call an Euclidean instanton is to be an oscillating instanton, if there exists a point where the derivative of the scale factor and the scalar field vanish at the same time. Then, we can prove that the oscillating instanton can be analytically continued, both as inhomogeneous and homogeneous tunneling channels. Here, we especially focus on the possibility of a homogeneous tunneling channel. For the existence of such an instanton, we have to assume three things: (1) there should be a local maximum and the curvature of the maximum should be sufficiently large, (2) there should be a local minimum and (3) the other side of the potential should have a sufficiently deeper vacuum. Then, we can show that there exists a number of oscillating instanton solutions and their probabilities are higher compared to the Hawking–Moss instantons. We also check the possibility when the oscillating instantons are comparable with the Coleman–de Luccia channels. Thus, for a general vacuum decay problem, we should not ignore the oscillating instanton channels.

We construct a Lie 3-algebra extended model of the IIB matrix model. It admits any Lie 3-algebra and possesses the same supersymmetry as the original matrix model, and thus as type IIB superstring theory. We examine dynamics of the model by taking minimal Lie 3-algebra that includes u(N) Lie-algebra as an example. There are two phases in the minimally extended model at least classically. The extended action reduces to that of the IIB matrix model in one phase. In other phase, it reduces to a more simple action, which is rather easy to analyze.

In this paper, we study several aspects of extremal spherical symmetric black hole solutions of four-dimensional N = 1 supergravity coupled to vector and chiral multiplets with the scalar potential turned on. In the asymptotic region, the complex scalars are fixed and regular which can be viewed as the critical points of the black hole and the scalar potentials with vanishing scalar charges. It follows that the asymptotic geometries are of a constant and nonzero scalar curvature which are generally not Einstein. These spaces could also correspond to the near horizon geometries which are the product spaces of a two anti-de Sitter surface and the two sphere if the value of the scalars in both regions coincide. In addition, we prove the local existence of nontrivial radius dependent complex scalar fields which interpolate between the horizon and the asymptotic region. We finally give some simple ℂⁿ-models with both linear superpotential and gauge couplings.

We consider a graviweak unification model with the assumption of the existence of a hidden (invisible) sector of our Universe, parallel to the visible world. This Hidden World (HW) is assumed to be a Mirror World (MW) with broken mirror parity. We start with a diffeomorphism invariant theory of a gauge field valued in a Lie algebra , which is broken spontaneously to the direct sum of the space–time Lorentz algebra and the Yang–Mills algebra: — in the ordinary world, and — in the hidden world. Using an extension of the Plebanski action for general relativity, we recover the actions for gravity, SU(2) Yang–Mills and Higgs fields in both (visible and invisible) sectors of the Universe, and also the total action. After symmetry breaking, all physical constants, including the Newton's constants, cosmological constants, Yang–Mills couplings, and other parameters, are determined by a single parameter g present in the initial action, and by the Higgs VEVs. The dark energy problem of this model predicts a too large supersymmetric breaking scale (M_SUSY ~10¹⁰GeV), which is not within the reach of the LHC experiments.

Based on recent theoretical developments (Cremaschini and Tessarotto, 2011–2013), in this paper the issue is addressed of the first-principle construction of the nonlocal relativistic radiation-reaction (RR) equation for classical spherical-shell, finite-size particles and antiparticles. This is achieved invoking the axioms of Classical Electrodynamics by means of the Hamilton variational principle. In connection with this, the Lagrangian conservation laws, together with the possible existence of adiabatic invariants, and the transformation laws of the RR equation with respect to CPT and time-reversal transformations are investigated. The latter properties make possible the parametrization of the RR equations, holding respectively for particles and antiparticles of this type, in terms of the same coordinate time t and the investigation of the qualitative properties of their solutions. In particular, in both cases the RR self-force is found to have the same signature, which implies that the dynamics of classical finite-size antiparticles is equivalent to that of classical extended particles of opposite charge. Therefore, in the framework of Classical Mechanics, a distinction between particles and antiparticles cannot be made based solely on the electromagnetic interactions associated with electromagnetic RR phenomena. As a basic application of the theory, the Lagrangian conservation laws and symmetry properties for the Hamiltonian asymptotic approximations of the exact RR equation are also addressed.

We explicitly study how jet substructure taggers act on a set of signal and background events. We focus on two-pronged hadronic decay of a boosted Z-boson. The background to this process comes from QCD jets with masses of the order of m_Z. We find a way to compare various taggers within a single framework by applying them to the most relevant splitting in a jet. We develop a tool, TOY-TAG, which allows one to get insight into what happens when a particular tagger is applied to a set of signal or background events. It also provides estimates for significance and purity. We use our tool to analyze differences between various taggers and potential ways to improve the performance by combining several of them.

We review the General Relativistic model of a (quasi-)pointlike particle represented by a massive shell of electrically charged matter, which displays an ADM mass M equal to the electric charge |Q| in the small-volume limit. We employ the Israel–Darboux's junction equations to explicitly derive this result, and then study the modifications introduced by the existence of a minimum length scale λ. For λ of the order of the Planck length (or larger), we find that the ADM mass becomes equal to the bare mass m₀ of the shell, like it occurs for the neutral case.

The statistical approach is used to calculate the parton distribution functions (PDFs) of the nucleon. At first it is assumed that the partons are free particles and the light-front kinematic variables are employed to extract the Bjorken x-dependence of the PDFs. These PDFs are used to evaluate the combinations of the sea quarks such as . As our first attempt to improve the result, we make the statistical parameters to depend on Q², using different values of Gottfried sum rule. The related results are indicating better behavior by accessing to the PDFs while they contain the Q² dependence parameters. As a further task and in order to have more improvement in the calculations, a linear potential is considered to describe the quark interactions. The solution of the related Dirac equation yields the Airy function and is considered as a wave function in spatial space. Using the Fourier transformation the wave functions are obtained in momentum space. Based on the light-front kinematic variables and using a special method which we call it "k-method," these functions can be written in terms of the Bjorken x-variable. Following that the statistical features are accompanied with these functions. Considering an effective approach which is used in this paper, we do not need to resort to any extra effects as were assumed in some papers to get proper results for PDFs. The obtained results for and the ratio, using our effective approach, are in good agreement with the available experimental data and some theoretical results.

It is shown in the case of proton scattering on an electron gas target that the Closed Time Path formalism can handle final state interactions of the target in equilibrium in a simple and natural manner. The leading-order cross-section is proportional to the photon density of states. The scattering needs a partial resummation of the perturbation series when the electron gas forms long living quasi-particles with high density of state during the collision. A strong cancellation between real and virtual electron-hole pairs is found in this case.