International Journal of Modern Physics A

The unexpected absence of unambiguous signals of New Physics (NP) at the TeV scale at the Large Hadron Collider (LHC) puts today flavor physics at the forefront. In particular, rare decays of b-hadrons represent a unique probe to challenge the Standard Model (SM) paradigm and test models of NP at a scale much higher than that accessible by direct searches. This article reviews the status of the field.

In this paper, we review the theoretical foundations of gravitational waves in the framework of Albert Einstein’s theory of general relativity. Following Einstein’s early efforts, we first derive the linearized Einstein field equations and work out the corresponding gravitational wave equation. Moreover, we present the gravitational potentials in the far away wave zone field point approximation obtained from the relaxed Einstein field equations. We close this review by taking a closer look on the radiative losses of gravitating $n$-body systems and present some aspects of the current interferometric gravitational waves detectors. Each section has a separate appendix contribution where further computational details are displayed. To conclude, we summarize the main results and present a brief outlook in terms of current ongoing efforts to build a spaced-based gravitational wave observatory.

In this paper, we study noncommutative massive unquenched Chern–Simons matter theory using its gravity dual. We construct this novel background by applying a TsT-transformation on the known parent commutative solution. We discuss several aspects of this solution to the Type IIA supergravity equations of motion and, amongst others, check that it preserves ${𝒩}=1$ supersymmetry. We then turn our attention to applications and investigate how dynamical flavor degrees of freedom affect numerous observables of interest. Our framework can be regarded as a key step toward the construction of holographic quantum Hall states on a noncommutative plane.

The proposal of the present work is to study the difference between the strange quark–antiquark amount in the proton and neutron. For this purpose, the possible nucleon–hyperon–kaon fluctuations are analyzed with the effective chiral theory. The small difference of particle masses is shown to be in the origin of this isospin asymmetry. The dependence of the results on the mass cutoff parameter and with the coupling constants is analyzed.

In this paper, we investigate the problem of ordinary baryonic matter accretion onto the noncommutative (NC) geometry-inspired Schwarzschild black hole. The fundamental equations governing the spherically symmetric steady state matter accretion are deduced. These equations are seen to be modified due to the presence of noncommutativity. The matter accretion rate is computed and is found to increase rapidly with the increase in strength of the NC parameter. The sonic radius reduces while the sound speed at the sonic point increases with the increase in the strength of noncommutativity. The profile of the thermal environment is finally investigated below the sonic radius and at the event horizon and is found to be affected by noncommutativity.

In this paper, we construct a map between a solution of supersymmetric Chern–Simons higher spin gravity based on the superalgebra $sl(3|2)$ with Lifshitz scaling and the $N=2$ super Boussinesq hierarchy. We show that under this map the time evolution equations of both theories coincide. In addition, we identify the Poisson structure of the Chern–Simons theory induced by gauge transformation with the second Hamiltonian structure of the super Boussinesq hierarchy.

Photoproduction of vector mesons is computed with dipole model in proton–proton ultraperipheral collisions (UPCs) at the CERN Large Hadron Collider (LHC). The dipole model framework is employed in the calculations of vector mesons production in diffractive processes. Parameters of the bCGC model are refitted with the latest inclusive deep inelastic scattering experimental data. Employing the bCGC model and boosted Gaussian light-cone wave function for vector mesons, we obtain the prediction of rapidity distributions of $J/\psi$ and $\psi (2s)$ mesons in proton–proton ultraperipheral collisions at the LHC. The predictions give a good description of the experimental data of LHCb. Predictions of $\varphi$ and $\omega$ mesons are also evaluated in this paper.

Lepton flavor violating (LFV) decays are forbidden in the Standard Model (SM) and to explore them one has to go beyond it. The flavor changing neutral current induced lepton flavor conserving and LFV decays of $K$ and $B$ mesons is discussed in the gauge group $G=SU{(2)}_L\times U{(1)}_{Y_1}\times SU{(2)}_X$. The lepto-quark $X_{\mu }^{\pm 2/3}$ corresponding to gauge group $SU{(2)}_X$ allows the quark–lepton transitions and hence giving a framework to construct the effective Lagrangian for the LFV decays. The mass of lepto-quark $m_X$ provides a scale at which the gauge group $G$ is broken to the SM gauge group. Using the most stringent experimental limit ${ℬ}(K_L^0\to {\mu }^{\mp }{e}^{\pm })<1.7\times 10^{-12}$, the upper bound on the effective coupling constant ${\left(\frac{G_X}{G_F}\right)}^2<1.1\times 10^{-10}$ is obtained for certain pairing of lepton and quark generations in the representation $(2,\bar{2})$ of the group $G$. Later, the effective Lagrangian for the LFV meson decays for the gauge group $G=[SU{(2)}_L\times SU{(2)}_R\times U{(1)}_{Y_1^{\prime }}]\times SU{(2)}_X$ is constructed. Using ${ℬ}(K^{-}\to {\pi }^{-}\nu \bar{\nu })=(1.7\pm 1.1)\times 10^{-10}$, the bound on the ratio of effective couplings is obtained to be ${\left(\frac{G_X}{G_F}\right)}^2<10^{-10}$. A number of decay modes are discussed which provide a promising area to test this model in the current and future particle physics experiments.

The strong CP problem is one of many puzzles in the theoretical description of elementary particle physics that still lacks an explanation. While top-down solutions to that problem usually comprise new symmetries or fields or both, we want to present a rather bottom-up perspective. The main problem seems to be how to achieve small CP violation in the strong interactions despite the large CP violation in weak interactions. In this paper, we show that with minimal assumptions on the structure of mass (Yukawa) matrices, they do not contribute to the strong CP problem and thus we can provide a pathway to a solution of the strong CP problem within the structures of the Standard Model and no extension at the electroweak scale is needed. However, to address the flavor puzzle, models based on minimal SU(3) flavor groups leading to the proposed flavor matrices are favored. Though we refrain from an explicit UV completion of the Standard Model, we provide a simple requirement for such models not to show a strong CP problem by construction.

We propose a model with an extra isospin doublet $U{(1)}_D$ gauge symmetry, in which we introduce several extra fermions with odd parity under a discrete $Z_2$ symmetry in order to cancel the gauge anomalies out. A remarkable issue is that we impose nonzero $U{(1)}_D$ charge to the Standard Model Higgs, and it gives the most stringent constraint to the vacuum expectation value of a scalar field breaking the $U{(1)}_D$ symmetry that is severer than the LEP bound. We then explore relic density of a Majorana dark matter candidate without conflict of constraints from lepton flavor violating processes. A global analysis is carried out to search for parameters which can accommodate with the observed data.

Based on the diquark configuration, we construct the diquark–antidiquark interpolating tetraquark currents with $J^{\mathrm{\text{PC}}}=1^{-\pm }$ and $1^{+\pm }$, which can couple to the scalar and pseudoscalar tetraquark states, respectively, since they are not conserved currents. Then, we investigate their two-point correlation functions including the contributions of the vacuum condensates up to dimension-10 and extract the masses and pole residues of the tetraquark states with $J^{\mathrm{\text{PC}}}=0^{+\pm }$ and $0^{-\pm }$ through the QCD sum rule approach. The predicted masses can be confronted with the experimental data in the future. Moreover, we briefly discuss the possible decay patterns of the tetraquark states.