Physics

In this paper we investigate an observable universe in Bianchi type V space-time by taking into account the cosmological constant as the source of energy. We have performed a χ 2 test to obtain the best fit values of the model parameters of the universe in the derived model. We have used two types of data sets, viz: i) 31 values of the Hubble parameter and ii) the 1048 Phanteon data set of various supernovae distance moduli and apparent magnitudes. From both the data sets, we have estimated the current values of the Hubble constant, density parameters ( Ω m ) 0 and ( Ω Λ ) 0 . The present value of deceleration parameter of the universe in derived model is obtained as q 0 = 0.59 +0.04 −0.03 and 0.59 +0.02 −0.03 in accordance with H(z) and Pantheon data respectively. Also we observe that there is a signature flipping in the sign of deceleration parameter from positive to negative and transition red-shift exists. Thus, the universe in derived model represents a transitioning universe which is in accelerated phase of expansion at present epoch. We have estimated the current age of the universe ( t 0 ) and present value of jerk parameter ( j 0 ) . Our obtained values of t 0 and j 0 are in good agreement with its values estimated by Plank collaborations and WMAP observations.

In an attempt to regularize a previously known exactly solvable model [Yang and Zhang, Eur. J. Phys. \textbf{40}, 035401 (2019)], we find yet another exactly solvable toy model. The interesting point is that while the Hamiltonian of the model is parameterized by a function f(x) defined on [0,∞) , its spectrum depends only on the end values of f , i.e., f(0) and f(∞) . This model can serve as a good exercise in quantum mechanics at the undergraduate level.

I argue that the marquis characteristics of the quantum-mechanical double-slit experiment (point detection, random distribution, Born rule) can be explained using Schroedinger's equation alone, if one takes into account that, for any atom in a detector, there is a small but nonzero gap between its excitation energy and the excitation energies of all other relevant atoms in the detector (isolated-levels assumption). To illustrate the point I introduce a toy model of a detector. The form of the model follows common practice in quantum optics and cavity QED. Each detector atom can be resonantly excited by the incoming particle, and then emit a detection signature (e.g. bright flash of light) or dissipate its energy thermally. Different atoms have slightly different resonant energies per the isolated-levels assumption, and the projectile preferentially excites the atom with the closest energy match. The toy model permits one easily to estimate the probability that any atom is resonantly excited, and also that a detection signature is produced before being overtaken by thermal dissipation. The end-to-end detection probability is the product of these two probabilities, and is proportional to the absolute square of the incoming wavefunction at the atom in question, i.e. the Born rule. I consider how closely a published neutron-interference experiment conforms to the picture developed here; I show how this paper's analysis steers clear of creating a scenario with local hidden variables; I show how the analysis steers clear of the irreversibility implicit in the projection postulate; and I discuss possible experimental tests of this paper's ideas. Hopefully, this is a significant step toward realizing the program of solving the measurement problem within unitary quantum mechanics envisioned by Landsman, among others.

The status of angles within The International System of Units (SI) has long been a source of controversy and confusion. We address one specific but crucial issue, putting the case that the idea of angles necessarily being length ratios, and hence dimensionless, is not valid. By making a clear distinction between the definition of a quantity and the process of making a measurement of that quantity, we show that the usual arguments for angles being length ratios are problematic. An appreciation of this point should clear away a major obstacle preventing a more proper treatment of the angle problem.

To produce a vortex, a torque must be applied to the fluid. In viscous fluids, the torques that produce turbulent vortices result from the loss of symmetry of the stress tensor, once the viscous friction exceeds the shear stress resistance of the fluid. In wall-bounded flows, in particular, the turbulent vortices form in a thin layer of fluid adjacent to the wall, practically coinciding with the so-called viscous sublayer, where the viscous friction reaches the largest values. The present paper determines a vortex structure for this sublayer, consistent with the well-known linearity of the diagram of the mean streamwise velocity of this region. The analysis enables us to calculate the diameter, angular velocity, and interaxis of the vortices in the viscous sublayer in steady-state conditions. The lifting force that makes the vortices migrate from the wall towards the mainstream flow is determined, and the crucial role played by gyroscopic precession in the reorientation of the vortex axis is discussed.

Anisotropic cloud string cosmological model with Bianchi type I space time is investigated in the context of general relativity. The exact solutions of Einstein field equations are obtained with when the source for energy momentum tensor is generated by a cloud of strings with particles attached to them. The dynamical and physical properties of the model universe are discussed by comparing with the present observational findings. The interesting feature obtained here is that our model universe starts with a big bang and as time passes both particle density and string tension density decreases with expansion of our Universe so that in the late time string vanishes and thus leaving only the particles.

We obtain a class of anisotropic spherically symmetric relativistic solutions of compact objects in hydrostatic equilibrium in the f(R,T)=R+2χT modified gravity, where R is the Ricci scalar, T is the trace of the energy momentum tensor and χ is a dimensionless coupling parameter. The matter Lagrangian is L m =− 1 3 (2 p t + p r ) , where p r and p t represents the radial and tangential pressures. Compact objects with dense nuclear matter is expected to be anisotropic. Stellar models are constructed for anisotropic neutron stars working in the modified Finch-Skea (FS) ansatz without preassuming an equation of state. The stellar models are investigate plotting physical quantities like energy density, anisotropy parameter, radial and tangential pressures in all particular cases. The stability of stellar models are checked using the causality conditions and adiabatic index. Using the observed mass of a compact star we obtain stellar models that predicts the radius of the star and EoS for matter inside the compact objects with different values of gravitational coupling constant χ . It is also found that a more massive star can be accommodated with χ<0 . The stellar models obtained here obey the physical acceptability criteria which show consistency for a class of stable compact objects in modified f(R,T) gravity.

We investigate a new class of LRS Bianchi type-II cosmological models by revisiting in the paper of Mishra {\it et al} (2013) by considering a new deceleration parameter (DP) depending on the time in string cosmology for the modified gravity theory suggested by S a ´ ez \& Ballester (1986). We have considered the energy-momentum tensor proposed by Leteliar (1983) for bulk viscous and perfect fluid under some assumptions. To make our models consistent with recent astronomical observations, we have used scale factor (Sharma {\it et al} 2018; Garg {\it et al} 2019) a(t)=exp[ 1 β 2βt+k − − − − − − √ ] , where β and k are positive constants and it provides a time-varying DP. By using the recent constraints ( H 0 =73.8 , and q 0 =−0.54 ) from SN Ia data in combination with BAO and CMB observations (Giostri {\it et al}, arXiv:1203.3213v2[astro-ph.CO]), we affirm β=0.0062 and k=0.000016 . For these constraints, we have substantiated a new class of cosmological transit models for which the expansion takes place from early decelerated phase to the current accelerated phase. Also, we have studied some physical, kinematic and geometric behavior of the models, and have found them consistent with observations and well established theoretical results . We have also compared our present results with those of Mishra {\it et al} (2013) and observed that the results in this paper are much better, stable under perturbation and in good agreement with cosmological reflections.

Formal solution of the Dirac equation in a nucleus field can be singular at the nucleus region. These singularities are cut off if the space is discrete. Electromagnetic interaction cannot be accounted for by perturbation theory. Under this interaction, treated self-consistently, the singularity smears out and the resulting physical states are referred to as anomalous. The anomalous states are additional to the set of usual atomic states. The binding energy of the anomalous state can be in the MeV region. That state cannot be populated under conventional experimental conditions. The anomalous electron state in the proton Coulomb field, referred to as anomalous boson, is of the size of 10 −12 cm and of approximately neutron mass.

The electron magnetic moment decomposition calculated in QED is proposed to have origin in a multi-vortex internal structure of the electron. This proposition is founded on two important contributions of the present work. First, a critical review on Weyl model of electron, Einstein-Rosen bridge and Wheeler's wormholes leads to a new idea of a topological defect in cylindrical space-time geometry as a natural representation of the electron. A concrete realization of this idea in terms of the derivation of a new vortex-metric, and its physical interpretation to establish the geometric origin of the electron magnetic moment decomposition constitute the second contribution. Remarkable occurrence of a vortex structure in the basis mode function used in BLFQ is also pointed out indicating wider ramification of the proposed electron model.