Challenging problems of particle physics and astrophysics. The preface

The preface to the special issue of IJMPD ”Challenging Problems of Particle physics and Astrophysics” briefly reviews some new ideas in the development of modern Astrophysics, Cosmology, Particle and Astroparticle physics inspired by discussions at the Fifth International Conference on Particle Physics and Astrophysics (ICPPA2020).

The μNet project: A status report

μNet aims at the deployment and long-term operation of an extensive school network of educational Cosmic Ray telescopes in the geographical area of Peloponnese. In the framework of μNet, an extended educational program will take place, encompassing educational activities for the construction, testing and operation of μCosmics (microCosmics) detectors, as well as for the remote operation of cosmic ray detection stations and astroparticle physics experimental devices deployed at the Hellenic Open University (HOU) campus. A pilot run of the μNet project started in 2020 aiming at the deployment and operation of a small school network in the prefecture of Achaea. In this work we present the progress of the program to date and the feedback we have received so far from the students and the teachers participating in it.

Astroparticle Physics with Compact Objects

Probing the existence of hypothetical particles beyond the Standard model often deals with extreme parameters: large energies, tiny cross-sections, large time scales, etc. Sometimes, laboratory experiments can test required regions of parameter space, but more often natural limitations lead to poorly restrictive upper limits. In such cases, astrophysical studies can help to expand the range of values significantly. Among astronomical sources, used in interests of fundamental physics, compact objects—neutron stars and white dwarfs—play a leading role. We review several aspects of astroparticle physics studies related to observations and properties of these celestial bodies. Dark matter particles can be collected inside compact objects resulting in additional heating or collapse. We summarize regimes and rates of particle capturing as well as possible astrophysical consequences. Then, we focus on a particular type of hypothetical particles—axions. Their existence can be uncovered due to observations of emission originated due to the Primakoff process in magnetospheres of neutron stars or white dwarfs. Alternatively, they can contribute to the cooling of these compact objects. We present results in these areas, including upper limits based on recent observations.

Multimessenger Astronomy with Neutrinos

Multimessenger astronomy is arguably the branch of the astroparticle physics field that has seen the most significant developments in recent years. In this manuscript, we will review the state-of-the-art, the recent observations, and the prospects and challenges for the near future. We will give special emphasis to the observation carried out with neutrino telescopes.

Multimessenger Astronomy with Neutrinos

Multimessenger astronomy is probably the branch of the astroparticle physics field that has seen more developments in recent years. In this manuscript we will review the state of the art, the recent observations, and the prospects and challenges for the near future. We will give special emphasis to the observation done with neutrino telescopes.

Research and development of scintillation detectors for the study of cosmic ray

At Bose Institute Prof. Debendra Mohan Bose and his co-workers made globally recognised contributions in the field of cosmic rays including the first recording of mu-meson tracks. Prof. D. M. Bose and Dr. Biva Choudhury did their cosmic ray experiments at the Darjeeling campus of Bose Institute (along with Sandakphu and Pharijong). Presently the Darjeeling campus hosts a National facility for Astroparticle Physics and Space Science. In Kolkata also there is a Centre for Astroparticle Physics and Space Science (CAPSS). In these two campuses, we are still working on the R\&D of plastic scintillation detectors for the study of the cosmic rays to preserve the legacy of Prof. D. M. Bose. The only cosmic ray air shower array in the eastern part of India, consisting of seven plastic scintillator detectors is commissioned at an altitude of about 2200~meters above sea level (a.s.l.) in the Eastern Himalayas (Darjeeling) at the end of January 2018. The cosmic ray air shower array has a hexagon shape with six detectors kept at the vertices ofthe hexagon and one at the center of it. The distance between two consecutive detectors is 8 meters. Each detectorelement is made up of four plastic scintillators of dimension 50~cm~$\times$~50~cm~$\times$~1~cm thereby forming a totalactive area of 1~m$^2$. These scintillators are fabricated indigenously in the Cosmic RayLaboratory (CRL), TIFR, Ooty, India. All four scintillators of a detector are coupled with a singlePhoto Multiplier Tube (PMT) using wavelength shifting (WLS) fibers. A custom-built module withseven inputs is used to generate a multi-fold trigger. Measurement of the number of cosmic ray airshower is going on since the end of January 2018. The secondary cosmic ray flux and its variation overtime are also recorded at the laboratory in Darjeeling using a three-fold coincidence technique withplastic scintillators. All the details of the experimental setup, techniques of measurement are reported earlier. The updates in the results are presented in this article. In this review article, the details of the R\&D program of plastic scintillation detectors carried out during the last five years, for the study of cosmic ray is reported.