International Journal of Modern Physics A

Highlights from Brookhaven National Laboratory (BNL) and experiments at the BNL Relativistic Heavy Ion Collider (RHIC) are presented for the years 2011–2013. This review is a combination of lectures which discussed the latest results each year at a three year celebration of the 50th anniversary of the International School of Subnuclear Physics in Erice, Sicily, Italy. Since the first collisions in the year 2000, RHIC has provided nucleus–nucleus and polarized proton–proton collisions over a range of nucleon–nucleon center-of-mass energies from 7.7 GeV to 510 GeV with nuclei from deuterium to uranium, most often gold. The objective was the discovery of the Quark Gluon Plasma, which was achieved, and the measurement of its properties, which were much different than expected, namely a "perfect fluid" of quarks and gluons with their color charges exposed rather than a gas. Topics including quenching of light and heavy quarks at large transverse momentum, thermal photons, search for a QCD critical point as well as measurements of collective flow, two-particle correlations and J/Ψ suppression are presented. During this period, results from the first and subsequent heavy ion measurements at the Large Hadron Collider (LHC) at CERN became available. These confirmed and extended the RHIC discoveries and have led to ideas for new and improved measurements.

It has been ten years since the first report for a positive strangeness pentaquark-like baryon state. However, the existence of the pentaquark state is still controversial. Some contradictions between the experiments are unsolved. In this paper, we review the experimental search for the pentaquark candidates Θ⁺, Θ⁺⁺, Ξ^{- -}, and N* in detail. We review the experiments with positive results and compare the experiments with similar conditions but opposite results.

Three families of quarks and leptons, one Higgs to rule them all, and in the darkness bind them.

We present some comments on Schwingers's calculation of electron–positron production in a prescribed constant electric field. The range of validity of 2 Im ℒ⁽¹⁾(E) is discussed thoroughly and limiting cases are provided.

A relativistic power-law potential model of independent quarks is used to study the leptonic decays of neutral vector mesons. Here, the transition probability amplitude for leptonic decay of meson is determined from the momentum distribution function which is found from the assumption of a strong correlation existing between the momenta of quark and antiquark inside the meson. The model parameters are first determined from the application of the model to study the ground state spectra of ρ, ω, ϕ, ψ and ϒ mesons together with the radiative decay widths of mesons. The same model with no adjustable parameters is then used to evaluate the leptonic decay widths and the electromagnetic decay constants for the vector mesons ρ, ω, ϕ, ψ and ϒ. The calculated results are in remarkable agreement with the corresponding experimental values.

The questions related to the consistent interpretation of QFT perturbative amplitudes are considered in light of a novel procedure, alternative to the traditional ones based on regularization prescriptions. A detailed discussion about the aspects associated to the space–time dimension is performed. For this purpose, it is considered a simple model having a fermionic vector current, coupled to a vector field, as well as a fermionic scalar current, coupled to a scalar field, both of them composed by different species of massive fermions. The referred currents are related in a precise way, which is reflected in the Ward identities for the perturbative physical amplitudes. The double vector two-point fermionic function, related to the vacuum polarization tensor of QED, as well as the amplitudes related to such quantity through relations among Green functions are explicit evaluated in space–time dimensions d = 2, 3, 4, 5 and 6. In the adopted procedure the perturbative amplitudes are not modified in intermediary steps of the calculations, as occurs in regularization procedures. Divergent Feynman integrals are not really solved. They appear only in standard objects, conveniently defined, where no physical parameter is present. Only very general properties for such quantities are assumed. For the finite parts, a set of functions is introduced which allows universal forms for the results. We show that scale independent, ambiguity free amplitudes are automatically obtained in a regularization independent way. As a consequence, interesting and, in certain way, surprising aspects are revealed in a clear and transparent way when the Ward identities and low-energy limits are verified for the simple amplitudes considered in the presently reported investigation. The obtained results suggest that the procedure can be considered as an advantageous tool to handle with the problem of divergences in perturbative solutions of QFT's, relative to the traditional regularization techniques, since the obtained results are so consistent as desirable and there are no limitations of applicability. In particular, the method can be applied in odd and even space–time dimensions having extra dimensions, which is not possible within the context of traditional regularization.

Hubble expansion in warped braneworld model is addressed in the presence of more than one warped extra dimensions. Some distinct phenomenological signatures of such model has already been discussed in the context of collider-based experiments as well as to explain the fermion mass hierarchy in the Standard Model of elementary particles. In this paper, we explore some cosmological implications of such a model. It is shown that while the expansion depends on all the moduli, an exponential nature of the expansion of the scale factor emerges as a generic feature which is independent of the number of extra dimensions but depends only on the bulk cosmological constant and brane pressure. A generalized expression for the effective 3-brane cosmological constant in such model has been derived. This generalizes the well-known fine tuning/detuning between the bulk cosmological constant and brane tension to obtain the desired cosmological constant on the brane. The warped factor corresponding to the higher-dimensional cosmological scenario is determined and the issue of gauge hierarchy problem is discussed.

We show performing general "0-brane reduction" along an arbitrary fixed direction in space–time and applied to the starting point of minimal, off-shell 4D, 𝒩 = 1 irreducible supermultiplets, yields adinkras whose adjacency matrices are among some of the special cases proposed by Kuznetsova, Rojas and Toppan. However, these more general reductions also can lead to "Garden Algebra" structures beyond those described in their work. It is also shown that for light-like directions, reduction to the 0-brane breaks the equality in the number of fermions and bosons for dynamical theories. This implies that light-like reductions should be done instead to the space of 1-branes or equivalently to the worldsheet.

We define Hermitian generalized Jordan triple systems and prove a structure theorem. We also give some examples of the systems and study mathematical properties. We apply a Hermitian generalized Jordan triple system to a field theory and obtain a Chern–Simons gauge theory.

The exact solution for the neutrino mass matrix of the Zee–Babu model is derived. Tribimaximal mixing imposes conditions on the Yukawa couplings, from which the normal mass hierarchy is preferred. The derived conditions give a possibility of Majorana maximal CP violation in the neutrino sector. We have shown that nonzero θ₁₃ is generated if Yukawa couplings between leptons almost equal to each other. The model gives some regions of the parameters where neutrino mixing angles and the normal neutrino mass hierarchy obtained are consistent with the recent experimental data.

We develop a theory of dark matter based on a previously proposed picture, in which a complex vacuum scalar field makes the universe a superfluid, with the energy density of the superfluid giving rise to dark energy, and variations from vacuum density giving rise to dark matter. We formulate a nonlinear Klein–Gordon equation to describe the superfluid, treating galaxies as external sources. We study the response of the superfluid to the galaxies, in particular, the emergence of the dark-matter galactic halo, contortions during galaxy collisions and the creation of vortices due to galactic rotation.

We investigate a new form of contribution for the anomalous magnetic moment of all particles. This common origin is displayed in the framework of a recent treatment of electrodynamics that is based on the introduction of an electromagnetic metric which has no gravitational character. This effective metric constitutes a universal pure electromagnetic process perceived by all bodies, charged or not charged. As a consequence, it yields a complementary explanation for the existence of anomalous magnetic moment for charged particles and even for noncharged ones like neutrinos.

We study microscopic entropy of the near-extremal rotating black hole in four-dimensional (4D) 𝒩 = 2 supergravity with four charges set pairwise equal from AdS₂/CFT₁ correspondence. This correspondence is realized in terms of asymptotic symmetries of the AdS₂ geometry and a two-dimensional near-horizon effective quantum theory of residual fields from a dimensional reduction proposed by Robinson and Wilczek. We compute the relevant central charge and derive the microscopic entropy of this near-extremal black hole by Cardy formula. Our results can be extended to more general near-extremal rotating black holes in 4D supergravity. They further support the notion that black hole entropy is generally controlled by near-horizon conformal symmetry.