International Journal of Modern Physics A

In the Standard Model the total lepton number is conserved. Thus, neutrinoless double-β decay, in which the total lepton number is violated by two units, is a probe of physics beyond the Standard Model. In this review we consider the basic mechanism of neutrinoless double-β decay induced by light Majorana neutrino masses. After a brief summary of the present status of our knowledge of neutrino masses and mixing and an introduction to the seesaw mechanism for the generation of light Majorana neutrino masses, in this review we discuss the theory and phenomenology of neutrinoless double-β decay. We present the basic elements of the theory of neutrinoless double-β decay, our view of the present status of the challenging problem of the calculation of the nuclear matrix element of the process and a summary of the experimental results.

The past decade witnessed a remarkable proliferation of exotic charmonium-like resonances discovered at accelerators. In particular, the recently observed charged states are clearly not interpretable as mesons. Notwithstanding the considerable advances on the experimental side, conflicting theoretical descriptions do not seem to provide a definitive picture about the nature of the so-called XYZ particles. We present here a comprehensive review about this intriguing topic, discussing both those experimental and theoretical aspects which we consider relevant to make further progress in the field. At this state of progress, XYZ phenomenology speaks in favor of the existence of compact four-quark particles (tetraquarks) and we believe that realizing this instructs us in the quest for a firm theoretical framework.

Emergent gravity is based on a novel form of the equivalence principle known as the Darboux theorem or the Moser lemma in symplectic geometry stating that the electromagnetic force can always be eliminated by a local coordinate transformation as far as space–time admits a symplectic structure, in other words, a microscopic space–time becomes noncommutative (NC). If gravity emerges from U(1) gauge theory on NC space–time, this picture of emergent gravity suggests a completely new quantization scheme where quantum gravity is defined by quantizing space–time itself, leading to a dynamical NC space–time. Therefore the quantization of emergent gravity is radically different from the conventional approach trying to quantize a phase space of metric fields. This approach for quantum gravity allows a background-independent formulation where space–time and matter fields are equally emergent from a universal vacuum of quantum gravity.

We continue our study of finite BRST–anti-BRST transformations for general gauge theories in Lagrangian formalism, initiated in [arXiv:1405.0790 [hep-th] and arXiv:1406.0179 [hep-th]], with a doublet λ_a, a = 1, 2, of anticommuting Grassmann parameters, and prove the correctness of the explicit Jacobian in the partition function announced in [arXiv:1406.0179 [hep-th]], which corresponds to a change of variables with functionally dependent parameters λ_a = U_aΛ induced by a finite Bosonic functional Λ(ϕ, π, λ) and by the anticommuting generators U_a of BRST–anti-BRST transformations in the space of fields ϕ and auxiliary variables π^a, λ. We obtain a Ward identity depending on the field-dependent parameters λ_a and study the problem of gauge dependence, including the case of Yang–Mills theories. We examine a formulation with BRST–anti-BRST symmetry breaking terms, additively introduced into the quantum action constructed by the Sp(2)-covariant Lagrangian rules, obtain the Ward identity and investigate the gauge independence of the corresponding generating functional of Green's functions. A formulation with BRST symmetry breaking terms is developed. It is argued that the gauge independence of the above generating functionals is fulfilled in the BRST and BRST–anti-BRST settings. These concepts are applied to the average effective action in Yang–Mills theories within the functional renormalization group approach.

In this paper the charged Higgs signal through triple or double Higgs production in a two Higgs doublet model (2HDM) type II is studied. The main production process is e⁺e^- →H⁺H^-H⁰ followed by the charged Higgs decay to a pair of τν and the neutral Higgs decay to . The alternative process H⁺W^-H⁰ is also included as a source of charged Higgs signal in the analysis. The focus is on a future e⁺e^- linear collider operating at . The final state under consideration is suitable for electroweak background rejection using the b-tagging tools. It is shown that although the signal cross-section is small, with a reasonable background suppression, high signal significance values are achievable at an integrated luminosity 500 fb^-1 depending on the charged Higgs mass, tan β and the CP-odd neutral Higgs mass. Finally results are quoted in terms of the signal significance for charged Higgs in the mass range 160 < m_H^± < 400 GeV.

We study the inclusive hadroproduction of B⁰, B⁺ and mesons at leading order in the Parton Reggeization Approach using the universal fragmentation functions extracted from the combined e⁺e^- annihilation data from CERN LEP1 and SLAC SLC colliders. We have described B-meson transverse momentum distributions measured in the central region of rapidity by the CDF Collaboration at Fermilab Tevatron and CMS Collaboration at LHC within uncertainties and without free parameters, applying Kimber–Martin–Ryskin unintegrated gluon distribution function in a proton. The forward B-meson production (2.0<y<4.5) measured by the LHCb Collaboration also has been studied and expected disagreement between our theoretical predictions and data has been obtained.

We study rare decays and in the framework of nonstandard neutrino interactions (NSIs). We calculate branching ratios of these decays. We explore the possibility for second generation of quarks in NSIs just like leptonic contribution in and . We study the dependence of on . We show that there exists a possibility for , also from this reaction and other two reactions, and . Three other processes, and are investigated with s quark in the loop for NSIs instead of d quark. Constraints on and are provided. We point out that constraints for both u and c quark are equal and similarly for d and s quarks the constraints are equal .

In recent papers, a microscopic model for the SM Higgs mechanism has been proposed, and an idea how to determine the 24 quark and lepton masses of all three generations has emerged in that framework. This idea is worked out in detail here by accommodating the fermion masses and mixings to microscopic parameters. The top quark mass can be given in terms of the Fermi scale and of certain exchange couplings of isospin vectors obeying a tetrahedral symmetry. The observed hierarchy in the family spectrum is attributed to a natural hierarchy in the microscopic couplings. The neutrinos will be shown to vibrate within the potential valleys of the system, thus retaining very tiny masses. This is related to a Goldstone effect inside the internal dynamics. A discussion of the quark and lepton mixing matrices is also included. The mixing angles of the PMNS matrix are calculated for an example set of parameters, and a value for the CP-violating phase is given.

Nonlinear modifications of quantum mechanics generically lead to nonlocal effects which violate relativistic causality. We study these effects using the functional Schrödinger equation for quantum fields and identify a type of nonlocality which causes nearly instantaneous entanglement of spacelike separated systems. We describe a simple example involving widely separated wave packet (coherent) states, showing that nonlinearity in the Schrödinger evolution causes spacelike entanglement, even in free field theory.