The European Physical Journal C

As has been done before, we study an unknown coupling function, i.e. $$F(\varphi )$$ , together with a function of torsion and also curvature, i.e. f(T) and f(R), generally depending upon a scalar field. In the f(R) case, it comes from quantum correlations and other sources. Now, what if beside this term in f(T) gravity context, we enhance the action through another term which depends upon both scalar field and its derivatives? In this paper, we have added such an unprecedented term in the generic common action of f(T) gravity such that in this new term, an unknown function of torsion has coupled with an unknown function of both scalar field and its derivatives. We explain in detail why we can append such a term. By the Noether symmetry approach, we consider its behavior and effect. We show that it does not produce an anomaly, but rather it works successfully, and numerical analysis of the exact solutions of field equations coincides with all most important observational data, particularly late-time-accelerated expansion. So, this new term may be added to the gravitational actions of f(T) gravity.

In this work, we present a new framework for five-dimensional spherical symmetry anisotropic stars that admits conformal motion. The behaviour of model characteristic pressure, stress, density profile and surface tension is investigated with the inclusion of a particular density profile for the higher dimensional Einstein’s field equations. All the physical parameters are well-behaved for the presented solution in higher dimensions. The analysis predict the possible existence of compact stars in five dimensions, more likely strange quark star.

Neutrino visible decay in the presence of matter is re-evaluated. We study these effects in two future long-baseline experiments where matter effects are relevant: DUNE (1300 km) and a hypothetical beam aimed towards ANDES (7650 km). We find that matter effects are negligible for the visible component of neutrino decay at DUNE, being much more relevant at ANDES. We perform a detailed simulation of DUNE, considering $$\nu _\mu $$ disappearance and $$\nu _e$$ appearance channels, for both FHC and RHC modes. The sensitivity to the decay constant $$\alpha _3$$ can be as low as $$2\times 10^{-6}$$  eV $$^2$$ at 90% C.L., depending on the neutrino masses and type of coupling. We also show the impact of neutrino decay in the determination of $$\theta _{23}$$ and $$\delta _\mathrm{CP}$$ , and find that the best-fit value of $$\theta _{23}$$ can move from a true value at the lower octant towards the higher octant.

Using the Regge-like formula $$(M-m_Q)^2=\pi \sigma L$$ between hadron mass M and angular momentum L with a heavy quark mass $$m_Q$$ and a string tension $$\sigma $$ , we analyze all the heavy–light systems, i.e., $$D/D_s/B/B_s$$ mesons and charmed and bottom baryons. Numerical plots are obtained for all the heavy–light mesons of experimental data whose slope becomes nearly equal to 1/2 of that for light hadrons. Assuming that charmed and bottom baryons consist of one heavy quark and one light cluster of two light quarks (diquark), we apply the formula to all the heavy–light baryons including the recently discovered $$\Omega _c$$ and find that these baryons experimentally measured satisfy the above formula. We predict the average mass values of B, $$B_s$$ , $$\Lambda _b$$ , $$\Sigma _c$$ , $$\Xi _c$$ , and $$\Omega _c$$ with $$L=2$$ to be 6.01, 6.13, 6.15, 3.05, 3.07, and 3.34 GeV, respectively. Our results on baryons suggest that these baryons can be safely regarded as heavy quark–light cluster configuration. We also find a universal description for all the heavy–light mesons as well as baryons, i.e., one unique line is enough to describe both of charmed and bottom heavy–light systems. Our results suggest that instead of mass itself, gluon flux energy is essential to obtain a linear trajectory. Our method gives a straight line for $$B_c$$ although the curved parent Regge trajectory was suggested before.

In this work we study a Hořava-like 5-dimensional model in the context of braneworld theory. The equations of motion of such model are obtained and, within the realm of warped geometry, we show that the model is consistent if and only if λ takes its relativistic value 1. Furthermore, we show that the elimination of problematic terms involving the warp factor second order derivatives are eliminated by imposing detailed balance condition in the bulk. Afterwards, Israel’s junction conditions are computed, allowing the attainment of an effective Lagrangian in the visible brane. In particular, we show that the resultant effective Lagrangian in the brane corresponds to a (3+1)-dimensional Hořava-like model with an emergent positive cosmological constant but without detailed balance condition. Now, restoration of detailed balance condition, at this time imposed over the brane, plays an interesting role by fitting accordingly the sign of the arbitrary constant β, insuring a positive brane tension and a real energy for the graviton within its dispersion relation. Also, the brane consistency equations are obtained and, as a result, the model admits positive brane tensions in the compactification scheme if, and only if, β is negative and the detailed balance condition is imposed.

The recently reported measurements of the CP asymmetry $a_{\psi K}$ by the BABAR and BELLE collaborations, obtained from the rate differences in the decays $B^0 \to (J/\psi K_s), (J/\psi K_L)$ etc., and their charge conjugates, are in good agreement with the standard model (SM) prediction of the same, resulting from the unitarity of the CKM matrix. The so-called minimal flavour violating (MFV) supersymmetric extensions of the standard model, in which the CKM matrix remains the only flavour changing structure, predict $a_{\psi K}$ similar to the one in the SM. With the anticipated precision in $a_{\psi K}$ and other CP asymmetries at the B factories and hadron colliders, one hopes to pin down any possible deviation from the SM. We discuss an extension of the MFV-supersymmetric models which comfortably accommodates the current measurements of the CP asymmetry $a_{\psi K}$ , but differs from the SM and the MFV-supersymmetric models due to an additional flavour changing structure beyond the CKM matrix. We suggest specific tests in forthcoming experiments in B physics. In addition to the CP-asymmetries in B-meson decays, such as $a_{\psi K}$ and $a_{\pi \pi}$ , and the mass difference $\Delta M_s$ in the $B_s^0 - \overline{B_s^0}$ system, we emphasize measurements of the radiative transition $b \to d \gamma$ as sensitive probes of the postulated flavour changing structure. This is quantified in terms of the ratio $R(\rho \gamma/K^* \gamma) = 2{\cal B}(B^0 \to \rho^0 \gamma)/{\cal B}(B^0 \to K^{* 0} \gamma)$ , the isospin violating ratio $\Delta^{\pm 0}={\cal B}(B^\pm \to \rho^\pm \gamma)/2{\cal B}(B^0 \to\rho^0 \gamma) -1$ , and the CP-asymmetry in the decay rates for $B^+ \to \rho^+ \gamma$ and its charge conjugate. Interestingly, the CKM–unitarity analysis in the Extended–MFV model also allows solutions $\bar\rho <0$ for the Wolfenstein parameter, as opposed to the SM and the MFV-supersymmetric models for which only $\bar\rho > 0$ solutions are now admissible, implying $\gamma > \pi/2$ , where $\gamma=-\arg V_{ub}$ . Such large values of $\gamma$ are hinted by the current measurements of the branching ratios for the decays $B\to \pi\pi$ and $B\to K \pi$ .

In this work, we present a new class of analytic and well-behaved solution to Einstein’s field equations describing anisotropic matter distribution. It’s achieved in the embedding class one spacetime framework using Karmarkar’s condition. We perform our analysis by proposing a new metric potential $$g_{rr}$$ which yields us a physically viable performance of all physical variables. The obtained model is representing the physical features of the solution in detail, analytically as well as graphically for strange star candidate SAX J1808.4-3658 ($$Mass=0.9 ~M_{\odot }$$, $$radius=7.951$$ km), with different values of parameter n ranging from 0.5 to 3.4. Our suggested solution is free from physical and geometric singularities, satisfies causality condition, Abreu’s criterion and relativistic adiabatic index $$\varGamma $$, and exhibits well-behaved nature, as well as, all energy conditions and equilibrium condition are well-defined, which implies that our model is physically acceptable. The physical sensitivity of the moment of inertia (I) obtained from the solutions is confirmed by the Bejger−Haensel concept, which could provide a precise tool to the matching rigidity of the state equation due to different values of n viz., $$n=0.5, 1.08, 1.66, 2.24, 2.82$$ and 3.4.

It is widely believed that the spin of black holes in X-ray binaries is mainly natal. A significant spin-up from accretion is not possible. If the secondary has a low mass, the black hole spin cannot change too much even if the black hole swallows the whole stellar companion. If the secondary has a high mass, its lifetime is too short to transfer the necessary amount of matter and spin the black hole up. However, while black holes formed from the collapse of a massive star with solar metallicity are expected to have low birth spin, current spin measurements show that some black holes in X-ray binaries are rotating very rapidly. Here we show that, if these objects are not the Kerr black holes of general relativity, the accretion of a small amount of matter ( $$\sim $$ 2  $$M_\odot $$ ) can make them look like very fast-rotating Kerr black holes. Such a possibility is not in contradiction with any observation and it can explain current spin measurements in a very simple way.