The Invisibles (2026)

Astroparticle Physics is the interface of particle physics, astrophysics, and cosmology. This is an exciting area of contemporary research which is going through its golden age - there is a lot of data, several important problems that have been identified, a few have been solved, and several more are expected to be solved within the next few decades.

This course will focus on the "Invisibles" -- neutrinos, dark matter, and gravitational waves -- 3 "dark" messengers that are relatively less well explored (compared to the old trustworthy friend -- photons).

The underlying theme of the course will be that

"Particle physics is the engine that drives the Universe" and "the Universe is a fantastic particle physics lab."
Various interesting aspects of astroparticle physics are best seen as effective theories / controlled approximations of a unified picture that simplify under special circumstances (separation of scales).
Owing to the special circumstances, one does not always need the full machinery of GR and QFT, but a heuristic approach using (glorified) dimensional analysis, etc. allow us to make a lot of progress.

The expected outcome of the course is that you will be able to

Perform order-of-magnitude and scaling analyses of key astroparticle processes.
Derive and interpret fundamental results in neutrinos, DM, and GW research.
Connect particle microphysics to cosmology and astronomical observables.
Understand and analyze experimental strategies across a variety of detection methods.
Synthesize multi-messenger observations to constrain models.

Target Audience

This is a "Topical Course" in the TIFR graduate school. Students who have joined after their B.Sc. or M.Sc may both take this course, but confirm with the SBP for administrative details.

Administrivia

Time: Tu, Th at 1730-1900

Venue: A304

Credit policy: TBA

Instructor: Basudeb Dasgupta

Course Contents

Here's a tentative syllabus (pdf file).

See Moodle [TIFR only] for Notes.

References

The Early Universe, Kolb and Turner
Modern Cosmology, Dodelson and Schmidt
Kim and Pevsner, Neutrinos in Physics and Astronomy
Stars as Laboratories for Fundamental Physics, Raffelt
Introduction to Particle Dark Matter, Profumo
Particle Dark Matter, ed. Bertone et al.
GW Physics and Astronomy, Creighton and Anderson
Gravitational waves, Maggiore

Lecture Plan

Day Zero (18 Aug): Course Overview

Lecture 1 (20 Aug): Units & Dimensional Analysis

Lecture 2 (25 Aug): Units & Dimensional Analysis

Lecture 3 (27 Aug): Numbers and Particles

Lecture 4 (1 Sep): Numbers and Particles

Lecture 5 (3 Sep): FRW Cosmology

Lecture 6 (8 Sep): Thermal History

Lecture 7 (10 Sep): Thermal History

Lecture 8 (15 Sep): Neutrinos in Cosmology, N_eff

Lecture 9 (16 Sep; NOTE the Date Change): Neutrinos in Cosmology, m_nu

Lecture 10 (23 Sep; NOTE the Date Change): Neutrino Oscillations, Super-K

Lecture 11 (24 Sep): Collective Neutrino Oscillations

Lecture 12 (29 Sep): Neutrinos in Stars: Energy Loss Argument

Lecture 13 (1 Oct): High-Energy Neutrinos

Lecture 14 (6 Oct): High-Energy Neutrinos, IceCube

Lecture 15 (8 Oct): Dark Matter: Evidence

Lecture 16 (13 Oct): WIMPs and Freezeout

Lecture 17 (15 Oct): Direct, Indirect Detection: LZ, Fermi

No Lecture (20 Oct): Dussehra

Lecture 18 (22 Oct): DM Structure Formation, WDM, SIDM

Lecture 19 (27 Oct): Axion DM: ADMX

Lecture 20 (29 Oct): Nonthermal and PBH

Lecture 21 (3 Nov): GWs

Lecture 22 (5 Nov): Binary Inspiral, LIGO

No Lectures on 10 and 12 Nov: Diwali Break

Lecture 23 (17 Nov): Hellings-Down and PTA

Lecture 24 (19 Nov): Phase Transitions and SGWs

No Lecture (24 Nov): Guru Nanak Jayanti

Lecture 25 (26 Nov): Putting it Together

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