About

Ratindranath Akhoury is a professor affiliated with the U-M LSA Physics Department. His research interests are in quantum field theory with applications to quantum gravity. He is also interested in problems at the intersection of quantum field theories and quantum information theory. His academic background includes a Ph.D. from The State University of New York, Stony Brook, obtained in 1980, an M.S. from the Indian Institute of Technology, India, in 1975, and a B.S. from Patna University, India, in 1973. He is based in the Randall Lab and Homer A. Neal Lab at the University of Michigan, Ann Arbor.

Research topics

• Physics
• Quantum mechanics
• Quantum electrodynamics
• Mathematics
• Mathematical physics

Selected publications

• Superrotations are Linkages

  arXiv (Cornell University) · 2025-07-06

  preprintOpen access1st authorCorresponding

  We show that superrotations can be described using the geometric conformal completion method of Penrose. In particular, superrotation charges can be described and calculated using the linkage method of Geroch and Winicour. Whether superrotation charges are calculated using the coordinate based Bondi formalism or the geometric Penrose formalism, the fact that the superrotation blows up at a point makes the superrotation charge formally ill defined. Nonetheless, we show that it can be made well defined through a regularization procedure devised by Flanagan and Nichols.

  PublisherOA PDFDOI

• Singular supertranslations and Chern-Simons theory on the black hole horizon

  Physical review. D/Physical review. D. · 2023-04-26 · 3 citations

  articleOpen access1st authorCorresponding

  We construct the standard and dual supertranslation charges on the future horizon of the Schwarzschild black hole, using the first-order formulation of gravity with the Holst action. The Dirac bracket algebra of standard and dual supertranslation charges is shown to exhibit a central term in the presence of singularities in the two-sphere function associated with supertranslation. We show that one can cancel this anomalous term and restore the asymptotic symmetry algebra by introducing a gravitational Chern-Simons theory on the horizon. This demonstrates that consistency of the asymptotic symmetry algebra requires a new structure on the horizon.

  PublisherOA PDFDOI

• Singular Supertranslations and Chern-Simons Theory on the Black Hole Horizon

  arXiv (Cornell University) · 2022-11-30 · 1 citations

  preprintOpen access1st authorCorresponding

  We construct the standard and dual supertranslation charges on the future horizon of the Schwarzschild black hole, using the first-order formulation of gravity with the Holst action. The Dirac bracket algebra of standard and dual supertranslation charges is shown to exhibit a central term in the presence of singularities in the two-sphere function associated with supertranslation. We show that one can cancel this anomalous term and restore the asymptotic symmetry algebra by introducing a gravitational Chern-Simons theory on the horizon. This demonstrates that consistency of the asymptotic symmetry algebra requires a new structure on the horizon.

  PublisherOA PDFDOI

• Holography from Singular Supertranslations on a Black Hole Horizon

  Physical Review Letters · 2022-11-22 · 4 citations

  articleOpen access1st authorCorresponding

  We investigate the standard and dual Bondi-Metzner-Sachs (BMS) supertranslation generators on a black hole horizon and draw some conclusions about black hole physics. Recently, it has been shown that in addition to conventional BMS supertranslation symmetries, there exists an additional infinite set of magnetic asymptotic symmetries, dual BMS supertranslations, again parametrized by a function on the two-sphere. We show that the Dirac bracket between these generators exhibits an anomalous central term when one parameter function exhibits a singularity in the complex stereographical coordinates on the sphere. In order to preserve general coordinate invariance, we demonstrate that this central term can be removed by postulating a holographic gravitational Chern-Simons theory on the horizon. This indicates that for an anomaly-free theory of quantum gravity in the presence of a black hole, one should include a boundary theory on the horizon.

  PublisherOA PDFDOI

• Holography from Singular Supertranslations on a Black Hole Horizon

  arXiv (Cornell University) · 2022-05-16 · 1 citations

  preprintOpen access1st authorCorresponding

  We investigate the standard and dual Bondi-Metzner-Sachs (BMS) supertranslation generators on a black hole horizon and draw some conclusions about black hole physics. Recently, it has been shown that in addition to conventional BMS supertranslation symmetries, there exists an additional infinite set of magnetic asymptotic symmetries, dual BMS supertranslations, again parametrized by a function on the two-sphere. We show that the Dirac bracket between these generators exhibits an anomalous central term when one parameter function exhibits a singularity in the complex stereographical coordinates on the sphere. In order to preserve general coordinate invariance, we demonstrate that this central term can be removed by postulating a holographic gravitational Chern-Simons theory on the horizon. This indicates that for an anomaly-free theory of quantum gravity in the presence of a black hole, one should include a boundary theory on the horizon.

  PublisherOA PDFDOI

• High energy scattering in perturbative quantum gravity at next-to-leading power

  Physical review. D/Physical review. D. · 2021 · 95 citations

  1st authorCorresponding
  • Physics
  • Quantum electrodynamics
  • Quantum mechanics

  We consider the relativistic scattering of unequal-mass scalar particles through graviton exchange in the small-angle high-energy regime. We show the self-consistency of expansion around the eikonal limit and compute the scattering amplitude up to the next-to-leading power correction of the light particle energy, including gravitational effects of the same order. The first power correction is suppressed by a single power of the ratio of momentum transfer to the energy of the light particle in the rest frame of the heavy particle, independent of the heavy particle mass. We find that only gravitational corrections contribute to the exponentiated phase in impact parameter space in four dimensions. For large enough heavy-particle mass, the saddle point for the impact parameter is modified compared to the leading order by a multiple of the Schwarzschild radius determined by the mass of the heavy particle, independent of the energy of the light particle.

  PublisherOA PDFDOI

• Entanglement, Renormalization and Effective Field Theories

  arXiv (Cornell University) · 2020-11-10

  preprintOpen accessSenior author

  We develop the idea that renormalization, decoupling of heavy particle effects from low energy physics and the construction of effective field theories are intimately linked to the momentum space entanglement of disparate modes of an interacting quantum field theory. Using unitary transformations to decouple these modes at the perturbative level, we show in a scalar field theoretical model with light and heavy fields, how renormalization may be consistently implemented and how the low energy effective field theory can be constructed. We also obtain a renormalization group equation in this framework and apply it to the scalar field theoretical model.

  PublisherOA PDFDOI

• Magnetic soft charges, dual supertranslations, and ’t Hooft line dressings

  Physical review. D/Physical review. D. · 2020 · 18 citations

  Senior authorCorresponding
  • Physics
  • Quantum electrodynamics
  • Quantum mechanics

  We construct the Faddeev-Kulish asymptotic states in a quantum field theory of electric and magnetic charges. We find that there are two kind of dressings: apart from the well-known (electric) Wilson line dressing, there is a magnetic counterpart which can be written as a 't Hooft line operator. The 't Hooft line dressings are charged under the magnetic large gauge transformation (LGT), but are neutral under electric LGT. This is in contrast to the Faddeev-Kulish dressings of electrons, which can be written as a Wilson line operator and are charged under electric LGT but neutral under magnetic LGT. With these dressings and the corresponding construction of the coherent states, the infrared finiteness of the theory of electric and magnetic charges is guaranteed. Even in the absence of magnetic monopoles, the electric and magnetic soft modes exhibit the electromagnetic duality of vacuum Maxwell theory. Using only the asymptotic form of three-point interactions in a field theory of electric and magnetic charges, we show that the leading magnetic dressings, like the leading electric ones, are exact in the field theory of electric and magnetic charges, in accordance with a conjecture of Strominger. We then extend the construction to perturbative quantum gravity in asymptotically flat spacetime, and construct gravitational 't Hooft line dressings that are charged under dual supertranslations. The duality in the quantum theory between the electric and magnetic soft charges and their dressings is thus made manifest.

  PublisherOA PDFDOI

• Subleading soft dressings of asymptotic states in QED and perturbative quantum gravity

  Journal of High Energy Physics · 2019-09-01 · 32 citations

  articleOpen accessSenior author

  A bstract We construct Faddeev-Kulish states in QED and perturbative quantum gravity to subleading order in the soft momentum expansion and to first order in the coupling constant, using the charge conservation formula of asymptotic symmetries associated with the tree-level subleading soft theorems. We demonstrate that the emission and absorption of soft photons/gravitons in dressed amplitudes vanish. The fact that no additional soft radiation may be added to a dressed amplitude supports the claim that, in the dressed state formalism, the soft and hard sectors of scattering processes are correlated. We also show that the dressed virtual amplitudes are equivalent to the infrared-finite part of the traditional amplitudes constructed using Fock states. Since there is no real soft radiation in the asymptotic Hilbert space, the dressed state formalism gives the same cross sections as the Bloch-Nordsieck method.

  PublisherOA PDFDOI

• BMS supertranslation symmetry implies Faddeev-Kulish amplitudes

  Journal of High Energy Physics · 2018-02-01 · 71 citations

  articleOpen accessSenior author

  We show explicitly that, among the scattering amplitudes constructed from eigenstates of the BMS supertranslation charge, the ones that conserve this charge, are equal to those constructed from Faddeev-Kulish states. Thus, Faddeev-Kulish states naturally arise as a consequence of the asymptotic symmetries of perturbative gravity and all charge conserving amplitudes are infrared finite. In the process we show an important feature of the Faddeev-Kulish clouds dressing the external hard particles: these clouds can be moved from the incoming states to the outgoing ones, and vice-versa, without changing the infrared finiteness properties of S matrix elements. We also apply our discussion to the problem of the decoherence of momentum configurations of hard particles due to soft boson effects.

  PublisherOA PDFDOI

Frequent coauthors

• V.I. Zakharov

  15 shared

• Sangmin Choi

  Centre de Physique Théorique

  12 shared

• David Garfinkle

  Oakland University

  11 shared

• Ryo Saotome

  University of Michigan–Ann Arbor

  9 shared

• Michael G. Sotiropoulos

  Deutsche Bank (Germany)

  7 shared

• George Sterman

  Stony Brook University

  7 shared

• Malcolm J. Perry

  7 shared

• C. Gauthier

  National Taiwan University

  7 shared