Aritra's Research

Axions, or their generalization, axionlike particles (ALPs) are the most promising cadidates for dark matter. Interestingly, axions are named after the detergent Axion, as they "clean-up" a fundamental problem with the Strong interaction, known as the Strong CP problem. Later it was realized that these hypothetical particles have properties that closely resembles to those of cold dark matter. In fact, although tiny, the ALP and electromagnetic fields interact that gives rise to observable phenomena. For example, the left- and right-circularly polarized photons travels at different speeds in an ALP field giving rise to achromatic rotation of the plane of polarization of a linearly polarized light known as birefringence. In the presence of magnetic fields, ALPs covert to photons, the Primakoff effect, giving rise to spectral-line type feature.

Intriguingly, the signatures of birefringence and Primakoff effect can be searched at radio frequencies by targeting suitable astrophysical systems. In Basu et al. (2021), Phys. Rev. Lett., 126, 191102, we made use of strong gravitational lensing of polarized quasars to search for birefringence signal from ALPs. Based on this technique, we are currently carrying out a joint JVLA and VLBA campaign to search for ALPs using a few lens systems.

Weakly-Interacting Massive Particles, or WIMPs for short, are another dark matter candidate. WIMPs are believed to be produced via thermal processes in a similar way as other particles in the Standard Model of particle physics. They self-annihilate such that their number density freezes as the expansion rate of the Universe becomes larger than their annihilation rate. WIMPs annihilate via various channels producing γ-rays and e^--e⁺ pairs. Dark matter-rich astrophysical systems are excellent laboratories to search for these WIMP annihilation products.

The e^--e⁺ pairs give rise to emission at radio frequencies via the synchrotron mechanism when they gyrate in magnetic fields. However, in order to search for such emission, one needs to choose appropriate systems that substantially lack primary electrons produced through standard astrophysical processes, such as, supernovae explosion. Dwarf spheroidal galaxies (dSphs) are one of such suitable systems. My interest in this regard is focussed towards understanding the properties of the synchrotron emission in terms of extent when e^--e⁺ are produced via WIMP annihilation, and via astrophysical processes. I am mainly studying the nature of the emission in the presence of decaying magnetic field, and how next generation telescopes, like, an upgared LOFAR2.0 and MeerKAT would contribute towards our quest of detecting signatures of WIMPs.

Since the discovery of the correlation in 1970's, a clear understanding of the origin of the radio-infrared correlation remains elusive. Sensitive observations with modern radio (VLA, uGMRT, LOFAR and MeerKAT) and space-based infrared (Spitzer and Herschel) telescopes have releaved that the correlation holds good in various galaxy types ranging from low mass dwarf irregular galaxies to massive ultra luminous infrared galaxies in the nearby and early Universe. In order to better understand the properties of the relation in nearby and high-redshift galaxies, I investigate the role cosmic evolution of magnetic fields and energy loss/gain mechanisms of cosmic ray electrons play in setting up the correlation.

Depending on the astrophysical system, their geometry, and the nature of the turbulent dynamo operating in them, magnetic field structures are expected to have widely different morphology and physical scales. Hence, a quantitative understanding of the morphology of the associated emission, e.g., via the synchrotron mechanism, is needed. For this, using high resolution magnetohydrodynamic (MHD) simulations, I study the properties of their broadband polarized emission. We aim to connect the statistical properties and morphological features to the underlying turbulence driving mechanism in the context of the interstellar and the intracluster medium.

Cosmic evolution of grand-design large-scale spiral magnetic fields in star-forming galaxies remains an open question in observational astronomy. Due to the faintness of cosmologically distant galaxies, a major tool for probing magnetic fields in them would be through statistical measurement of Faraday rotation measure (RM) towards quasar absorption line systems. I study, how RM measured towards high metallicity DLAs can be used to infer about the large-scale field strengths, and how Fast Radio Bursts (FRBs) can be used to distinguish the field structure. 

Along with colleagues at the MPIfR and the Bielefeld University, we demonstrated that all-sky survey using the SKA-MPG telescope would play a crucial role in robustly pinning down the polarized synchrotron foreground in the 1.75--3.5 GHz frequency range to study the polarized Cosmic Microwave Background (CMB) Radiation down to nK (10^-9 K) accuracy. Such an accuracy is critical for future CMB space missions, e.g., the LiteBIRD, to detect CMB's B-mode polarization on large angular scales (>10^o) originating from primordial gravitational waves.

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