Modern Physics Letters A

We review the current status of searches for new physics beyond the Standard Model in the diphoton channel at the LHC and estimate the reach with future collected data. We perform a model independent analysis based on an effective field theory approach and different production mechanisms. As an illustrative example, we apply our results to a scenario of minimal composite dynamics.

In the version¹ of this paper we presented for the first time the basic equations and relations for relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG). This model is locally equivalent to the f(R) theory of gravity and gives an alternative description of the effects of dark matter and dark energy using the Brans–Dicke dilaton $\mathrm{\Phi }$. To outline the basic properties of the MDG model of SSSS and to compare them with general relativistic results, in this paper we use the relativistic equation of state (EOS) of neutron matter as an ideal Fermi neutron gas at zero temperature. We overcome the well-known difficulties of the physics of SSSS in the f(R) theories of gravity${}^{2,3}$ applying novel highly nontrivial nonlinear boundary conditions, which depend on the global properties of the solution and on the EOS. We also introduce two pairs of new notions: cosmological–energy–pressure densities and dilaton–energy–pressure densities, as well as two new EOSs for them: cosmological EOS (CEOS) and dilaton EOS (DEOS). Special attention is paid to the dilatonic sphere (in brief — disphere) of SSSS, introduced in this paper for the first time. Using several realistic EOS for neutron star (NS): SLy, BSk19, BSk20 and BSk21, and current observational two-solar-masses-limit, we derive an estimate for scalar-field-mass $m_{\mathrm{\Phi }}\sim 10^{-13}\mathrm{\text{eV}}/c^2÷4\times 10^{-11}\mathrm{\text{eV}}/c^2$. Thus, the present version of the paper reflects some of the recent developments of the topic.

We investigate cosmological constraints on the original relaxion scenario proposed by Graham, Kaplan and Rajendran. We first discuss the appropriate sign choice of the terms in the scalar potential, when the QCD axion is the relaxion with a relaxion–inflaton coupling proposed in the original paper. We next derive the cosmologically consistent ranges of the mass and a coupling of the relaxion for both the QCD relaxion and non-QCD relaxion. The mass range is obtained by $10^{-5}\mathrm{\text{eV}}\ll m_{\varphi }\lesssim 10^4\mathrm{\text{eV}}$. We also find that a strong correlation between the Hubble parameter at the relaxion stabilization and the scale $\mathrm{\Lambda }$ of non-QCD strong dynamics, which generates the non-perturbative relaxion cosine potential. For a higher relaxion mass, a large scale $\mathrm{\Lambda }$ becomes available. However, for its lower mass, $\mathrm{\Lambda }$ should be small and constructing such a particle physics model is challenging.

We show that by combining the elementary Goldstone–Higgs scenario and supersymmetry it is possible to raise the scale of supersymmetry breaking to several TeVs by relating it to the spontaneous-symmetry-breaking one. This is achieved by first enhancing the global symmetries of the super-Higgs sector to SU(4) and then embedding the electroweak sector and the Standard Model (SM) fermions. We determine the conditions under which the model achieves a vacuum such that the resulting Higgs is a pseudo-Goldstone boson (pGB). The main results are: the supersymmetry-breaking scale is identified with the spontaneous-symmetry-breaking scale of SU(4) which is several TeVs above the radiatively induced electroweak scale; intriguingly the global symmetry of the Higgs sector predicts the existence of two super-Higgs multiplets with one mass eigenstate playing the role of the pseudo-Goldstone Higgs; the symmetry-breaking dynamics fixes $\mathrm{\text{tan}}\beta =1$ and requires a supplementary singlet chiral superfield. We finally discuss the spectrum of the model that now features the superpartners of the SM fermions and gauge bosons in the multi-TeV range.

We investigate dynamics of probe particles moving in the near-horizon limit of (2N + 1)-dimensional extremal Myers–Perry black hole (in the cases of N = 3, 4, 5) with arbitrary rotation parameters. Very recently it has been shown in [T. Hakobyan, A. Nersessian and M. M. Sheikh-Jabbari, Phys. Lett. B 772, 586 (2017)] that in the most general cases with non-equal nonvanishing rotational parameters the system admits separation of variables in N-dimensional ellipsoidal coordinates. We wrote down the explicit expressions of Liouville integrals of motion, given in the above-mentioned reference in ellipsoidal coordinates, in initial “Cartesian” coordinates in seven, nine and eleven dimensions, and found that these expressions hold in any dimension. Then, taking the limit where all of the rotational parameters are equal, we reveal that each of these N − 1 integrals of motion results in the Hamiltonian of the spherical mechanics of a (2N + 1)-dimensional MP black hole with equal nonvanishing rotational parameters.

In this paper, we investigate the thermodynamical properties of Schwarzschild–Beltrami–de Sitter (S–BdS) black hole introduced by Yan et al. in 2013 by introducing inertial Beltrami coordinates to traditional non-inertial Schwarzschild–de Sitter (S–dS) metric which is the exact static spherical symmetry solution of Einstein equation with a positive cosmological constant $\mathrm{\Lambda }$. Based on this new metric, we compute entropy on all horizons and we give the entropy bound of the black hole. Hawking temperatures are calculated by considering a perturbation to entropy relations due to that the spacetime described by these inertial coordinates is no longer a stationary spacetime in which surface gravity related to Hawking temperature is defined well on killing horizon. We also get the Smarr relations and the first law of thermodynamics. We find that the S–BdS black hole seems to have similar thermodynamical properties to S–dS black hole in the comparison between their corresponding thermodynamical quantities, although the new black hole metric is described by inertial coordinates which exclude the effects of inertial force.

We take the viewpoint that the physically acceptable solutions of the Lorentz–Dirac equation for radiation back-reaction are actually determined by a second-order equation of motion, the self-force being given as a function of spacetime location and velocity. We propose three different methods to obtain this self-force function. For two example systems, we determine the second-order equation of motion exactly in the non-relativistic regime via each of these three methods, leading to the same result. We reveal that, for both systems considered, back-reaction induces a damping proportional to velocity and, in addition, it decreases the effect of the external force.