International Journal of Modern Physics A

The ATLAS and CMS collaborations have performed studies of a wide range of Standard Model processes using data collected at the Large Hadron Collider at center-of-mass energies of 7, 8 and 13 TeV. These measurements are used to explore the Standard Model in a new kinematic regime, perform precision tests of the model, determine some of its fundamental parameters, constrain the proton parton distribution functions, and study new rare processes observed for the first time. Examples of recent Standard Model measurements performed by the ATLAS and CMS collaborations are summarized in this report. The measurements presented span a wide range of event final states including jets, photons, W/Z bosons, top quarks, and Higgs bosons.

Next year we will celebrate 100 years of the cosmological term, $\mathrm{\Lambda }$, in Einstein’s gravitational field equations, also 50 years since the cosmological constant problem was first formulated by Zeldovich, and almost about two decades of the observational evidence that a nonvanishing, positive, $\mathrm{\Lambda }$-term could be the simplest phenomenological explanation for the observed acceleration of the Universe. This mixed state of affairs already shows that we do no currently understand the theoretical nature of $\mathrm{\Lambda }$. In particular, we are still facing the crucial question whether $\mathrm{\Lambda }$ is truly a fundamental constant or a mildly evolving dynamical variable. At this point the matter should be settled once more empirically and, amazingly enough, the wealth of observational data at our disposal can presently shed true light on it. In this short review, I summarize the situation of some of these studies. It turns out that the $\mathrm{\Lambda }=\mathrm{\text{const}}$. hypothesis, despite being the simplest, may well not be the most favored one when we put it in hard-fought competition with specific dynamical models of the vacuum energy. Recently, it has been shown that the overall fit to the cosmological observables SNIa+BAO+H(z)+LSS+BBN+CMB do favor the class of “running” vacuum models (RVM’s) — in which $\mathrm{\Lambda }=\mathrm{\Lambda }(H)$ is a function of the Hubble rate — against the “concordance” $\mathrm{\Lambda }$CDM model. The support is at an unprecedented level of $\sim 4\sigma$ and is backed up with Akaike and Bayesian criteria leading to compelling evidence in favor of the RVM option and other related dynamical vacuum models. I also address the implications of this framework on the possible time evolution of the fundamental constants of Nature.

Experimental era of rare $B$-decays started with the measurement of $B\to K^{\ast }\gamma$ by CLEO in 1993, followed by the measurement of the inclusive decay $B\to X_s\gamma$ in 1995, which serves as the standard candle in this field. The frontier has moved in the meanwhile to the experiments at the LHC, in particular, LHCb, with the decay $B^0\to {\mu }^{+}{\mu }^{-}$ at about 1 part in 10${}^{10}$ being the smallest branching fraction measured so far. Experimental precision achieved in this area has put the standard model to unprecedented stringent tests and more are in the offing in the near future. I review some key measurements in radiative, semileptonic and leptonic rare $B$-decays, contrast them with their estimates in the SM, and focus on several mismatches reported recently. They are too numerous to be ignored, yet, standing alone, none of them is significant enough to warrant the breakdown of the SM. Rare $B$-decays find themselves at the crossroads, possibly pointing to new horizons, but quite likely requiring an improved theoretical description in the context of the SM. An independent precision experiment such as Belle II may help greatly in clearing some of the current experimental issues.

Recently neutrino oscillation experiments have shown that it is very likely that there are one or two sterile neutrinos. In this review neutrino oscillations with one, two, three sterile and three active neutrinos, and parameters that are consistent with experiments, are reviewed.

Hadronic resonance propagators which take into account the analytical properties of decay processes are built in terms of the dispersion relation technique. Such propagators can describe multi-component systems, for example, those when quark degrees of freedom create a resonance state, and decay products correct the corresponding pole by adding hadronic deuteron-like components. Meson and baryon states are considered, examples of particles with different spins are presented.

Supersymmetric lattice Ward–Takahashi identities are investigated perturbatively up to two-loop corrections for super doubler approach of $N=2$ lattice Wess–Zumino models in 1- and 2-dimensions. In this approach, notorious chiral fermion doublers are treated as physical particles and momentum conservation is modified in such a way that lattice Leibniz rule is satisfied. The two major difficulties to keep exact lattice supersymmetry are overcome. This formulation defines, however, nonlocal field theory. Nevertheless we confirm that exact supersymmetry on the lattice is realized for all supercharges at the quantum level. Delicate issues of associativity are also discussed.

The derivation of the Glauber type representation for the high energy scattering amplitude of particles of spin 1/2 is given within the framework of the Dirac equation in the Foldy–Wouthuysen (FW) representation and two-component formalism. The differential cross-sections on the Yukawa and Gaussian potentials are also considered and discussed.

It is shown that electro (magneto) static sector of Maxwell’s electrodynamics coupled to the dilaton field in a string theory form possesses the symmetry group of the stationary General Relativity in vacuum. Performing the Ernst formalism, we develope a technique for generation of exact solutions in this modified electrodynamics on the base of the normalized Ehlers symmetry transformation. In the electrostatic case, we construct and study a general class of spherically symmetric solutions that describes a pointlike source of the Coulomb type. It is demonstrated that this source is characterized by finite and singularity-free interaction at short distances. Also it is established that the total electrostatic energy of this source is finite and inversely proportional to the dilaton-Maxwell coupling constant.

In this paper, we investigate the thermodynamics of a Yukawa-like model, constituted of a complex scalar field interacting with real scalar and vector fields, in the presence of an external magnetic field and boundaries. By making use of mean-field approximation, we analyze the phase structure of this model at effective chemical equilibrium, under change of values of the relevant parameters of the model, focusing on the influence of the boundaries on the phase structure. The findings reveal a strong dependence of the nature of the phase structure on temperature, magnetic background and size of compactified coordinate, with possibility of a two-step phase transition.

The charged black hole thermodynamics is corrected in terms of the quantum gravity effects. Most of the quantum gravity theories support the idea that near the Planck scale, the standard Heisenberg uncertainty principle should be reformulated by the so-called Generalized Uncertainty Principle (GUP) which provides a perturbation framework to perform required modifications of the black hole quantities. In this paper, we consider the effects of the minimal length and maximal momentum as GUP type I and the minimal length, minimal momentum and maximal momentum as GUP type II on thermo dynamics of the charged TeV-scale black holes. We also generalized our study to the universe with the extra dimensions based on the ADD model. In this framework, the effect of the electrical charge on thermodynamics of the black hole and existence of the charged black hole remnants as a potential candidate for the dark matter particles are discussed.

We consider the higher-order gravity theory derived from the quadratic Lagrangian $R+𝜖R^2$ in vacuum as a first-order (ADM-type) system with constraints, and build time developments of solutions of an initial value formulation of the theory. We show that all such solutions, if analytic, contain the right number of free functions to qualify as general solutions of the theory. We further show that any regular analytic solution which satisfies the constraints and the evolution equations can be given in the form of an asymptotic formal power series expansion.