Particle Physics
The Particle Physics Group at the Department of Theoretical Physics, TIFR, is dedicated to advancing our understanding of the fundamental forces and constituents of nature through the lens of quantum field theory. The group explores a wide spectrum of topics ranging from the structure and dynamics of the Standard Model, to proposed extensions that address open questions in particle physics, to theoretically interpreting experimental results from a wide array of experiments (high energy colliders, neutrino experiments, low energy experiments, etc.). Past and current members of the group have made significant contributions in understanding the QCD phase diagram; in predicting the spectrum of QCD resonances; in building tools and analyses for collider physics; in the physics of flavor, neutrino masses and mixings; in building models beyond Standard Model physics etc.
Members
Saumen Datta
Amol S. Dighe
Sandeepan Gupta
Nilmani Mathur
Tuhin S. Roy
Rishi Sharma
Areas of Interests
Building Models Beyond the Standard Model (BSM)
The "Standard Model" of particle physics describes nature at an extremely short distance scale in terms of fundamental constituents such as quarks, leptons, and gauge bosons; interacting via the "strong" and "electroweak" forces. Research in model building is aimed at formulating consistent and elegant theoretical models that provide further ultraviolet (UV) completion to the Standard Model and at the same time provide solutions to the pressing issues of the Standard Model such as the Hierarchy problem, Flavor problem, Strong CP problem etc. to name a few. Models are often constructed within a few paradigms. These include, for example, the framework of weak scale supersymmetry, embedding the electroweak theory within a strongly coupled sector, theories with extra spatial dimensions, collective symmetry breaking or rather its implementation in Little Higgs theories, cosmic selection etc. Projects often begin with a given issue of the Standard Model, or even issues with certain classes of BSM scenarios; attempt to formulate consistent theoretical models; and subsequently explore their observable consequences.
Collider Physics
The Large Hadron Collider (LHC) probes the laws of nature at length scales smaller than 10⁻¹⁹ meters, i.e. about a ten-thousandth of the radius of a hydrogen atom nucleus. The energy scale this corresponds to is the teraelectronvolt (TeV) scale. Accessing this scale is fundamentally important because it directly unlocks the physics of the Higgs boson, allowing scientists to meticulously study its properties, interactions, and central role in the mechanism of mass generation. Furthermore, this energy range is of immense theoretical interest; foundational concepts in particle physics strongly suggest that "new physics"—novel particles or forces beyond the Standard Model—should logically emerge at an energy scale not too far removed from the mass of the Higgs boson itself in order to stabilize it.
Ever since the Higgs boson was discovered in 2012, a detailed study of its properties has been an unambiguous goal of particle physics research. The LHC with its current luminosity can only partially achieve this goal as the precision with which it can measure Higgs boson couplings can barely exceed the 10% level because of systematic effects. Furthermore, some of the Higgs boson couplings such as its all-important self coupling cannot be measured at all by the LHC unless it is much larger than Standard Model expectations. A long-term program involving the high-luminosity LHC (HL-LHC) and proposed future colliders such as the Future circular collider (FCC) is thus being conceived at the international level. The theoretical high energy physics group, with its deep expertise in effective field theory, collider physics, machine learning techniques etc, is playing a key role in this global effort.
New phases of QCD in heavy ion collisions and neutron stars
Quantum Chromodynamics (QCD) predicts that under extreme conditions of temperature and density, hadronic matter undergoes a phase transition into a deconfined state where quarks and gluons are no longer confined within individual protons or neutrons. This state, known as the Quark-Gluon Plasma (QGP), is believed to have permeated the entire universe during the first few microseconds following the Big Bang.
QGP is experimentally studied in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and at the LHC. Hydrodynamic modelling of these collisions, an activity intensely pursued by members, suggests that a thermally equilibrated plasma is created very shortly after the collision and this plasma has a viscosity over entropy ratio small compared to most of the fluids encountered in daily life. One method of probing this hydrodynamic medium is by studying how it affects the propagation of heavy or energetic particles: a subject being pursued here.
On the other extreme end, for values of the chemical potential much larger than the QCD scale, but at small temperatures, deconfined matter will be a cold plasma of quarks and gluons, where the quarks will exist in some form of a color superconducting phase. This form of matter can exist in neutron stars, and members of the group are trying to understand how their presence can affect the structure of neutron stars and their dynamics.
QCD in the non-perturbative regime and hadronic physics
Non-perturbative Quantum Chromodynamics (QCD) explores the low-energy, strongly coupled regime of the strong interaction where the standard perturbative techniques break down. This demands the use of lattice simulations, effective field theories, or analytical non-perturbative methods such as bootstrap techniques to develop an understanding of this regime. However, understanding this regime is conceptually essential to gain insight into color confinement, the dynamical breaking of chiral symmetry, and the underlying mechanisms responsible for generating the mass spectrum of hadronic matter.
The properties of hadrons (composite subatomic particles) can be computed quantitatively from first principles using lattice QCD formulated on 3+1-dimensional space-time lattices, supported by large-scale high-performance computing. Our group investigates the energy spectra, structures, and interactions of hadrons, including conventional baryons and mesons, as well as exotic multi-quark states such as tetraquarks, pentaquarks, hybrids, glueballs, and exotic nuclei. Our calculations have successfully predicted the spectra of particles later confirmed experimentally, and continue to provide inputs for ongoing and future experiments, including those at CERN (LHC), Belle II, BESIII, and PANDA experiment, where many such states are expected to be observed. Another central focus of our research is to understand nuclear physics directly from its fundamental constituents—quarks and gluons. This involves addressing the emergence of nuclear phenomena, including the origin of binding in light nuclei, which has direct relevance to Big Bang nucleosynthesis and early-universe cosmology. After successfully addressing the challenging Wick-contraction problem for nuclei, we are now developing approaches to overcome the other major bottleneck–the signal-to-noise problem in nuclear correlation functions, using modern techniques, including AI. Our long-term objective is to enable first-principles studies of nuclear scattering processes, with implications for nuclear physics, beyond the Standard Model physics, astrophysics, and cosmology. Future research directions of the group also include the physics program of the Electron-Ion Collider at Brookhaven National Laboratory.
In parallel, the high-energy group also works on understanding strongly coupled theories like QCD in the non-perturbative regime using analytical frameworks. For instance a direction of research the group is involved in is supersymmetric QCD which provides a calculable model that may share qualitative features with real QCD. Another direction of research being pursued is the use of bootstrap methods to constrain the masses and spins of mesons in large N QCD.
Flavor Physics
In the Standard Model of particle physics, there are six quarks and six leptons, which form three families of matter particles. The masses and mixings of these particles are often referred to as the Flavor sector of the Standard Model. The Flavor problem in the Standard model involves understanding these patterns. Often in models trying to solve the Flavor problem, or even in various extensions of the Standard Model, there are observational consequences in these masses and mixings. Determination of quark mixing (CKM matrix) are, therefore, precision tests of the Standard Model, since these may bear hints of physics beyond the Standard Model.
Flavor physics has thus provided a rich program for indirect tests of the SM, by providing precision measurements that are sensitive to new physics at scales much higher than the electroweak scale. In the next decade, data from multiple channels such as meson and baryon decays as well as processes in the charged lepton sector, is expected to flow in from experiments such as Belle-II, NA62, Mu2e-II, MEG-II etc.
The particle physics group is interested in developing framework for understanding the physics of mesons and baryons, in developing tools and techniques for extracting information from flavor physics data, and in looking for new physics by calculating their observational consequences and comparing them with data.
Neutrino Physics at the Intensity and Cosmic Frontiers
Neutrinos are elusive, electrically neutral elementary particles that were long assumed to be completely massless within the Standard Model. However, the groundbreaking observation of neutrino oscillations—a purely quantum mechanical phenomenon where a neutrino created with a specific lepton flavor (electron, muon, or tau) can spontaneously transform into a different flavor as it travels—definitively proved that they must possess non-zero, albeit very small, masses. This oscillation occurs because the distinct flavor states produced during weak interactions are actually coherent superpositions of different mass eigenstates
Precise measurements of neutrino mixing parameters and search for new interactions of neutrinos, is one of the major goals of the worldwide high energy physics community. This involves long baseline experiments such as DUNE and T2K / T2H, as well as large detectors that can detect atmospheric and astrophysical neutrinos, such as IceCube and HyperKamiokande. The high energy group is actively involved in this effort and is interested in studying the impact of sterile neutrinos, non-standard interactions (NSI) and matter effects on neutrino oscillation phenomenology.
Members of the group have also made important contributions to other areas of neutrino physics such as tomography of the Earth using neutrinos, the possibility of neutrino mass generation from ultralight dark matter and the impact of neutrino mass/mixings in astrophysical scenarios (for more about this topic see the Cosmology page).
Quantum computing and AI applications
Quantum computing is emerging as a transformative paradigm with the potential to advance scientific and technological problem-solving across disciplines. A key component of this effort is the development of quantum algorithms that can be implemented on current and next-generation quantum hardware. Linear algebra underpins much of modern scientific and technological computation, and quantum linear solvers offer a promising route to overcome classical limitations, particularly for large-scale systems. As part of a collaboration under the National Quantum Mission, together with colleagues from DTP and the School of Computer Science and Technology, we are exploring and exploiting quantum algorithms with the goal of addressing problems in strongly interacting quantum many-body systems, including QCD. In parallel, we are exploring AI-based approaches, focusing on (i) generative models for statistical configuration sampling, (ii) accelerated diagonalization of large-scale matrices, (iii) inverse problems, and (iv) methods to mitigate the sign problem.