Journal Club


"Neutrino spin flavour precession in magnetised white dwarf"

Adhikary Jyotismita (NCBJ, Warsaw)

Due to notoriously small value of the neutrino magnetic moment, the phenomena of neutrino spin flavour precession (SFP) requires very high magnetic field. This makes only a handful of systems suitable to study this phenomena. By the observation of SFP, the Dirac and Majorana nature of neutrinos is expected to be distinguished. My talk will be based on the paper: "Neutrino spin flavour precession in magnetised white dwarf" DOI 10.1088/1361-6471/acd46b. In this work, we pointed out the potential of white dwarf (WD) system in studying the spin-flavour oscillation of neutrinos. The findings include: spin flavour transition probability of Dirac neutrinos is much higher in comparison to the Majorana neutrino which converts the active neutrino flavours to sterile in a significant amount and along with that, the neutrino magnetic moment plays a very sensitive role in the process.

J. Adhikary et al., eprint arXiv:2207.09485 (2022)


"A multiphase study of theoretical and observed light curves of classical Cepheids in the Magellanic Clouds"

Felipe Espinoza Arancibia (NCAC, Warsaw)

We present an analysis of the theoretical and observed light-curve parameters of the fundamental mode (FU) classical Cepheids in the Magellanic Clouds in V- and I- photometric bands. The state-of-the-art 1D non-linear radial stellar pulsation (RSP) code in MESA (MESA-RSP) has been utilized to generate the theoretical light curves using four sets of convection parameters. Theoretical light curves with two chemical compositions: Z = 0.008 and Z = 0.004 appropriate for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), respectively, covered a wide range of periods (3 1), and all periods. The multiphase relations obtained from theoretical and observed light curves in the PL/PC/AC plane are found to be dynamic in nature, with the effect more pronounced at Φ ~ 0.75-0.85. Furthermore, a contrasting behaviour of the theoretical/observed multiphase PL and PC relations between the short and long periods has been found for both LMC and SMC. The analysis shows that multiphase PL relations are more stringent to test the models with observations over the FPs. Distances to the LMC/SMC determined using long period Cepheids are found to be in good agreement with the literature values when the term R21 is added to the PL relation.

K. Kurbah et al., MNRAS (2023)


"Emergence of hot corona and truncated disk in simulations of accreting stellar mass black holes"

Parikshit Biswas (NCAC, Warsaw)

Stellar mass black holes in X-ray binaries (XRBs) are known to display different states characterized by different spectral and timing properties, understood in the framework of a hot corona coexisting with a thin accretion disk whose inner edge is truncated. There are several open questions related to the nature and properties of the corona, the thin disk, and dynamics behind the hard state. This motivated us to perform two-dimensional hydrodynamical simulations of accretion flows onto a 10 solar masses black hole. We consider a two-temperature plasma, incorporate radiative cooling with bremmstrahlung, synchrotron and comptonization losses and approximate the Schwarzschild spacetime via a pseudo-Newtonian potential. We varied the mass accretion rate in the range 0.02 ≤ Ṁ/Ṁ_Edd ≤ 0.35. Our simulations show the natural emergence of a colder truncated thin disk embedded in a hot corona, as required to explain the hard state of XRBs. We found that as Ṁ increases, the corona contracts and the inner edge of the thin disk gets closer to the event horizon. At a critical accretion rate 0.02 ≤ Ṁ_crit \Ṁ_Edd ≤ 0.06, the thin disk disappears entirely. We discuss how our simulations compare with XRB observations in the hard state.

R. Nemmen et al., eprint arXiv:2305.11429 (2023)