Modern Physics Letters A

B meson radiative effective neutral current ("penguin") decays rates, including the b → sγ and b → dγ transitions, represent one of the most powerful indirect constraints on new physics scenarios. Approaches to the measurements of the b → sγ width are presented, and the combined result is compared to its Standard-Model expectation. Various approaches to studying the b → dγ transition involve a comparison to corresponding b → sγ processes, and are presented in terms of the extracted ratio of CKM coupling parameters |V_td/V_ts|, which is precisely constrained within the context of the Standard Model by measurements of B meson mixing. The relative accuracy of experimental constraints on radiative penguin transition rates are better than ±7% for b → sγ and ±20% for b → dγ/b → sγ. The implications of the increasingly precise complementary constraint on |V_td/V_ts| that arises from the measurement radiative penguin decay widths may not yet be fully appreciated. There is significant potential for the improvement of these constraints in both the near (particularly for b → sγ) and longer terms.

The vacuum fluctuations of all quantum fields filling the universe are supposed to leave enormous energy and pressure contributions which are incompatible with observations. It has been recently suggested that, when the effective nature of quantum field theories is properly taken into account, vacuum fluctuations behave as a relativistic gas rather than as a cosmological constant. Accordingly, zero-point energies are tremendously diluted by the universe expansion but provide an extra contribution to radiation energy. Ongoing and future cosmological observations could offer the opportunity to scrutinize this scenario. The presence of such additional contribution to radiation energy can be tested by using primordial nucleosynthesis bounds or measured on Cosmic Background Radiation anisotropy.

We study the Large Hadron Collider (LHC) discovery potential for Z' models with continuously distributed mass for , 10 and 14 TeV center-of-mass energies. One of the possible LHC signatures for such models is the existence of broad resonance structure in Drell–Yan reaction pp →Z' + ⋯→l⁺l^- + ⋯.

The f(G) gravity is a theory to modify the general relativity and it can explain the present cosmic accelerating expansion without the need of dark energy. In this paper the f(G) gravity is tested with the energy conditions. Using the Raychaudhuri equation along with the requirement that the gravity is attractive in the FRW background, we obtain the bounds on f(G) from the SEC and NEC. These bounds can also be found directly from the SEC and NEC within the general relativity context by the transformations: ρ → ρ_m + ρ_E and p → p_m + p_E, where ρ_E and p_E are the effective energy density and pressure in the modified gravity. With these transformations, the constraints on f(G) from the WEC and DEC are obtained. Finally, we examine two concrete examples with WEC and obtain the allowed region of model parameters.

This paper deals with general thermodynamics for the universe filled with a perfect fluid, obeying an equation of state p = ω(z)ρ where the varying equation of the state parameter is chosen as two-index parametrization models namely: (a) linear redshift parametrization: ω(z) = ω₀ + ω₁z or (b) Jassal–Bagla–Padmanabhan (JBP) parametrization: where ω₀, ω₁ are constants. The behavior of temperature and the thermodynamic stability have been discussed. The thermal equation of state depends on both temperature and volume. As the universe evolves the fluid cools down obeying third law of thermodynamics and there will be thermodynamic stability during the expansion process without any phase transition or passing through any critical point.

In this paper we consider FRW cosmology in modified gravity which contains arbitrary functions f(ϕ). It is shown that the bouncing solution appears in the model whereas the equation of state (EoS) parameter crosses the phantom divider. The reconstruction of the model is also investigated with the aim to reconstruct the arbitrary functions and variables of the model.

A class of non-static solutions to the Einstein field equations has been investigated in the context of Bianchi type-V spacetime in a family of scalar–tensor theories in the presence as well as absence of the magnetic field. The physical and kinematical behaviors of the models have been discussed. The energy conditions of the models have also been verified.

For any odd k, a connection is established between the dihedral and supersymmetric extensions of the Tremblay–Turbiner–Winternitz Hamiltonians H_k on a plane. For this purpose, the elements of the dihedral group D_2k are realized in terms of two independent pairs of fermionic creation and annihilation operators and some interesting trigonometric identities are demonstrated.