Curvature singularity inf(R)theories of gravity

Abstract

Although f (R) modification of late time cosmology is successful in explaining present cosmic acceleration, it is difficult to satisfy the fifth-force constraint simultaneously. Even when the fifth-force constraint is satisfied, the effective scalar degree of freedom may move to a point (close to its potential minima) in the field space where the Ricci scalar diverges. We elucidate this point further with a specific example of f (R) gravity that incorporates several viable f (R) gravity models in the literature. In particular, we show that the nonlinear evolution of the scalar field in pressureless contracting dust can easily lead to the curvature singularity, making this theory unviable.

Model-independent investigation of rare semileptonic b→ulν¯l decay processes

“…[21-23], B → η ( ) lν l processes are studied by using various model-dependent approaches. The model independent analysis of b → ulν l processes can be found in [15]. Our predicted SM values of the branching ratios ofB (s) → P + l −ν l processes are found to be consistent with the predicted results in the literature, though due to updated input parameters, the central values of the branching ratios of these processes have slight deviations.…”

“…We then compute the branching ratios, forward-backward asymmetries and various LNU parameters of semileptonic B → (π, ρ, η ( ) )lν l and B s → K ( * ) lν l processes. Although these processes have been extensively studied in the literature [14][15][16][17][18][19][20][21][22][23][24], in the context of various new physics models and also in model-independent way, but the search for lepton nonuniversality parameters are not being explored.…”

Combining experiments and relativistic theory for establishing accurate radiative quantities in atoms: The lifetime of the 2P3/2 state in CaMeir1, Sinhal2, Safronova3 et al. 2020Phys. Rev. A10160View full textAdd to dashboardCite

“…The experimentally measured values, however, follow the exact formulas for these parameters and hence the ratio given in Eq. [3] in the main text does not equate exactly to A, but it differs by a small amount,…”

“…According to Eq. [3] of the main text, the ratio of three experimentally measured parameters (Γ, ∆E, ∆) equals to the sum of the transitions rates A P 3/2 →S 1/2 + A P 3/2 →D 5/2 which we will denote as A from now on for brevity. This equality holds for the approximate equations of the ac-Stark shift (Eq.…”

“…The knowledge of radiative lifetimes, transition rates, dipole-matrix elements and branching ratios in atoms and molecules is of great importance for, e.g., experiments probing the electroweak force [1][2][3] in the search of physics beyond the standard model, for testing and improving atomic and molecular-structure theories [3,4], for the development of atomic clocks [3,5,6] and for the interpretation of astronomical data [7].…”