Photoionization of ground and excited states of Ti I

Detailed photoionization of ground and many excited states with autoionizing resonances of neutral Ti are presented. Ti I with 22 electrons forms a large number of bound states, the present work finds a total of 908 bound states with n $⩽$ 10 and $l⩽8$. Photoionization cross sections (${\sigma }_{\mathit{PI}}$) for all these bound states have been obtained. Calculations were carried out in the close-coupling R-matrix method using a wave function expansion that included 36 states of core ion Ti II. It is found that the resonances enhance the low energy region of photoionization of the ground and low lying excited states. The resonant features will increase the opacity, as expected of astrophysical observation, and hence play important role in determination of abundances in the elements in the astronomical objects. The excited states also show prominent structures of Seaton or photo-excitation-of-core resonances.     

Photoionization of Ca XV with high energy features

Photoionization cross sections of (Ca XV + hν → Ca XVI + e), with high energy resonant photo-absorption phenomena, of a large number of bound states, 701 in total with n ≤ 10 and l ≤ 9, are reported. They are obtained using the R-matrix method with a close coupling (CC) wavefunction expansion of 29 states of n = 2,3 complexes of the core ion Ca XVI. Characteristic features found in photoionization of the ion are illustrated with examples. The cross section (σ_PI) of the ground 2s²2p²(³P) state is found to be unaffected by the size of the wavefunction expansion except for weak sparse resonances in high energy region. However, effects on excited states are considerable as the core excitations to n = 3 states are manifested in huge resonant absorption in high energy photoionization. They show existence of prominent high peak resonant features and enhancement in the background that were not studied before for Ca XV. In addition photoionization of the excited states with a single valence electron is dominated by Seaton resonant structures formed by the photo-excitation-of-core in the high energy region. These features will impact other quantities, such as the opacity, electron-ion recombination in high temperature plasmas where the ion exists, and hence will play important role in determination of elemental abundances in the astronomical objects.     

Coupling between cold dark matter and dark energy from neutrino mass experiments

We consider cosmological models with dynamical dark energy (dDE) coupled to cold dark matter (CDM), while simultaneously allowing neutrinos to be massive. Using a MCMC approach, we compare these models with a wide range of cosmological data sets. We find a strong correlation between this coupling strength and the neutrino mass. This correlation persists when BAO data are included in the analysis. We add then priors on $\nu$ mass from particle experiments. The claimed detection of $\nu$ mass from the Heidelberg–Moscow neutrinoless double-$\beta$ decay experiment would imply a 7–$8\sigma$ detection of CDM–DE coupling. Similarly, the detection of $\nu$ mass from coming KATRIN tritium $\beta$ decay experiment will imply a safe detection of a coupling in the dark sector. Previous attempts to accommodate cosmic phenomenology with such possible $\nu$ mass data made recourse to a $w<-1$ eoS. We compare such an option with the coupling option and find that the latter allows a drastic improvement.     

On the discovery of new behaviour in the oscillation of HD 101065

A 9 h of observation through high-speed B photometry was carried out on HD 101065 using the 0.5-m telescope of the South African Astronomical Observatory (SAAO). These photometric data were obtained between 2013 April 21 and June 19, in search of temporal variations in the oscillation of HD 101065. The frequency analysis of our data sets shows that the known principal frequency of oscillation (${\nu }_1=1.37287$ mHz) is still much intact. On nightly basis, we detected the presence of secondary frequencies (ν₂) that are well resolved from the principal frequency (ν₁) in the region of 1.0 mHz (P ∼ 17 min). These frequencies with very good signal-to-noise ratio have no harmonic period ratio with the principal frequency (ν₁). Furthermore, the amplitude spectra of individual nights reveal that the newly detected frequency (ν₂) is undergoing amplitude modulation on a short time-scale of few hours.     

Photoionization of fine structure levels of Ne III

Detailed study on the characteristic features in photoionization of Ne III, (hν + Ne III → Ne VI + e) is reported. The calculations were carried out in relativistic Briet–Pauli R-matrix (BPRM) method and close-coupling (CC) approximation. The CC expansion for the wavefunction of Ne III includes 58 fine structure levels of Ne IV from configurations 2s²2p³, 2s2p⁴, 2p⁵, 2s²2p²3s, 2s²2p²3p, 2s²2p²3d. The photoionization cross section (σ_PI) features exhibit i) presence of prominent resonances in the low energy region near the ionization thresholds of low lying levels, ii) lower energy region of extensive narrow Rydberg resonances and slow decaying background cross section in the high energy region for equivalent electron levels, and iii) presence of strong Seaton resonances due to photo-excitation-of-core (PEC) in the high energy region. The relativistic effects have almost no impact on the σ_PI in the high energy regions. However, for a number of low lying levels the coupling of fine structure channels, which is not allowed in LS coupling, introduces high-peak narrow resonances with almost zero background below the excitation threshold of 2s²2p³(²D^o) level of the residual ion. These will enhance quantities such as electron-ion recombination, opacity at very low temperature. The Seaton resonances due to n=3 PECs in the high energy region, which was not studied before, are more prominent than those for n=2 PECs. For complete modeling of astrophysical and laboratory plasmas, photoionization cross sections are presented for a large number of excited levels, in total 392, with n ≤ 10 and l ≤ 9.     

Cross section and astrophysical S-factor for 12C(p,γ)13N* reaction with Halo Effective Field Theory at low-energies

We considered one of the proton halo nuclei candidates, ¹³N* nucleus, and calculated the cross section and astrophysical S-factor for ¹²C(p, γ)¹³N* reaction using halo effective field theory without pion (hEFT${}^{\neg \pi }$). The halo effective field theory is used to examine the halo nucleus bound state with a large S-wave scattering length. We calculated the radiative proton capture cross section and the astrophysical S-factor from the fields of the core and the valence proton at the Leading-Order (LO). We showed that there is a good agreement among the our results for cross section and astrophysical S-factor of the ¹²C(p, γ)¹³N* reaction and the experimental data. The astrophysical S-factor that has been estimated at the zero energy (E_cm=0) by using a theoretical calculation of the cross section for direct radiative capture and an extrapolation of this calculation obtained $S\left(0\right)=1.883\times {10}^{-3}$ MeV-b.     

Photon in a cavity – a Gedankenexperiment

The inertial and gravitational mass of electromagnetic radiation (i.e., a photon distribution) in a cavity with reflecting walls has been treated by many authors for over a century. After many contending discussions, a consensus has emerged that the mass of such a photon distribution is equal to its total energy divided by the square of the speed of light. Nevertheless, questions remain unsettled on the interaction of the photons with the walls of the box. In order to understand some of the details of this interaction, a simple case of a single photon with an energy $E_{\nu }=h\nu$ bouncing up and down in a static cavity with perfectly reflecting walls in a constant gravitational field $\mathit{g}$, constant in space and time, is studied and its contribution to the weight of the box is determined as a temporal average.