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Publications
Arjun Kudinoor, Arthur Lin, Daniel Pablos, Krishna Rajagopal
Arjun Kudinoor, Arthur Lin, Daniel Pablos, Krishna Rajagopal
Ultra-relativistic oxygen-oxygen (OO) collisions are a promising arena in which to probe rare, large-angle, high momentum-transfer 2→2 Molière scatterings between energetic jet partons and quasiparticles in quark-gluon plasma (QGP). As a jet propagates through the droplet of QGP formed in the same collision, its constituents lose energy to and excite wakes in the medium, and may scatter off quark- and gluon-like quasiparticles in QGP. Using the hybrid strong/weak coupling model, we show that including Molière scatterings between jet partons and medium quasiparticles is essential to reproduce recent CMS measurements of charged-particle suppression in OO collisions with this model. We then present the first theoretical study of how jet-medium interactions modify the internal structure of jets in OO collisions. We find that Molière scatterings broaden the Soft Drop splitting angle Rg, enhancing the population of R = 0.4 and R = 0.8 jets with Rg ≳ 0.2 in OO collisions relative to pp collisions. Energy-energy correlators (EECs) provide a complementary probe, exhibiting enhanced large-angle correlations within jets due to jet-induced wakes and Molière scattering. In both cases, we propose an experimental measurement where the relevant OO/pp ratio can, if enhanced above unity in future data as in our calculations, be a distinctive, model-independent, detection of hard scattering off QGP quasiparticles. We furthermore use our calculations of EECs to show how the angular scale corresponding to the deflection of jet or medium partons by Molière scattering is imprinted in the EEC for jets with radius R ∼ 0.8 in OO collisions. These results demonstrate that jet substructure measurements in OO collisions are promising avenues to probe the quasiparticles that emerge at short distances within an otherwise strongly coupled medium.
Zachary Hulcher, Arjun Kudinoor, Daniel Pablos, Krishna Rajagopal
Zachary Hulcher, Arjun Kudinoor, Daniel Pablos, Krishna Rajagopal
Quark-gluon plasma (QGP) is a strongly coupled liquid when viewed at length scales of order the inverse of its temperature and longer. However, when it is probed at short enough length scales, asymptotic freedom mandates the presence of quark- and gluon-like quasiparticles. Partons in jets can trigger perturbative, high momentum-exchange 2→2 Molière scatterings off quasiparticles in the medium, making jets useful probes of the microscopic structure of QGP. Prior to this work, soft strongly coupled momentum-exchanges between jet partons and the QGP droplet produced in a heavy-ion collision, as well as the wakes that jets excite in the droplet, had been accounted for in the Hybrid Model of jet quenching. Here, we present a full calculation of Molière scattering off a QGP quasiparticle which results in the deflection of the jet parton and the excitation of a parton from the thermal medium that recoils after being kicked, and describe how it is implemented in the Hybrid Model. The scattered jet and recoil partons continue to propagate through the QGP, lose energy and momentum, excite wakes, and may further re-scatter. Using the Hybrid Model, we study how Molière scatterings impact jet shapes and fragmentation functions, the Soft Drop angle Rg, jet girth g, and observables that focus on the number and angular distribution of subjets within jets. We demonstrate that photon-tagged jets provide a particularly sensitive probe: selecting events by the photon energy mitigates the selection bias inherent in inclusive jet measurements and enhances sensitivity to rare large-angle scatterings. We find that Molière scatterings broaden both the Rg and g distributions when jets significantly softer than the photon are included. Our results point the way towards distinctive model-independent experimental signatures of hard scattering of jet partons off quasiparticles in QGP.
Arjun Kudinoor, Daniel Pablos, Krishna Rajagopal
Arjun Kudinoor, Daniel Pablos, Krishna Rajagopal
We show that recent measurements of substructure-dependent jet suppression constrain the value of the resolution length of the droplets of quark-gluon plasma (QGP) formed in heavy ion collisions. This resolution length is defined such that the medium can only resolve partons within a jet shower that are separated by more than the resolution length. We first use Hybrid Model calculations to reproduce ALICE measurements of the scaled Soft Drop angle θg for anti-kt R=0.2 jets reconstructed from charged-particle tracks. We find that the narrowing of the θg-distribution in PbPb collisions compared to pp collisions that is seen in the ALICE data rules out an infinte resolution length, where each entire parton shower loses energy to the plasma as if it were a single unresolved colored object. We then use Hybrid Model calculations to reproduce ATLAS measurements of dR12, the Soft Drop angle obtained by applying the Soft Drop grooming procedure to all charged-particle tracks in R=1 jets reconstructed from R=0.2 skinny subjets. Our analysis demonstrates that the ATLAS measurements of RAA for such R=1 jets as a function of dR12 are inconsistent with a zero-valued resolution length, where every splitting in a parton shower is immediately resolved by the plasma. We find that our Hybrid Model calculations agree best with the ATLAS measurements if QGP has a finite, nonzero, resolution length ∼(1−2)/(πT). For the first time, jet substructure measurements are constraining the resolution length of QGP from below, as well as from above.
Arjun Kudinoor, Daniel Pablos, Krishna Rajagopal
Arjun Kudinoor, Daniel Pablos, Krishna Rajagopal
The ATLAS Collaboration has developed a method to analyze large-radius jets composed of skinny R = 0.2 subjets in heavy-ion collisions. We first demonstrate that the measurements pioneered by ATLAS constrain the value of the resolution length of QGP -- and rule out any picture in which an entire parton shower loses energy coherently as a single entity. We then analyze the response of the medium to the passage of large-radius R=2 jets containing two skinny subjets in gamma-jet events. We introduce novel jet-shape observables that allow us to visualize how the internal structure of large-radius jets shapes the wakes they excite in the QGP. We find that even when the subjets are ∼0.8 radians apart, the angular shape of the soft hadrons originating from their wake forms a single broad structure. Only when the two subjets are even farther apart are two sub-wakes revealed. We show that the way in which jet structure shapes the structure of jet-induced wakes can be visualized with similar clarity in experiments by using only low-pT hadrons. The observables we introduce offer a new and distinctive way of seeing jet-induced wakes -- and wake substructure -- in heavy-ion collision data.
Hannah Bossi, Arjun Kudinoor, Ian Moult, Daniel Pablos, Ananya Rai, Krishna Rajagopal
Hannah Bossi, Arjun Kudinoor, Ian Moult, Daniel Pablos, Ananya Rai, Krishna Rajagopal
We use the hybrid strong/weak coupling model of heavy ion collisions to simulate interactions between energetic sprays of particles and the quark gluon plasma (QGP) that is created after a high-energy collision between large nuclei. These sprays of particles (called jets) leave behind wakes in the QGP. We show that hadrons originating from wakes are the dominant contribution to the three-point energy correlation function in the regime where the three points are well-separated in angle, forming a roughly equilateral triangle. This equilateral region of the correlator is far from the region populated by collinear emissions in the absence of QGP (the vacuum), making this equilateral region a canvas on which jet wakes can be imaged. Our work is a key step towards the systematic use of energy correlators to image and unravel the dynamical response of a droplet of QGP to a passing jet.
Arjun Kudinoor
Arjun Kudinoor
March 31, 2023
March 31, 2023
My senior thesis on differential geometry and gauge theory in physics. I focus on the study of the Yang--Mills equations, their self-dual solutions (instantons), and a proof of the Atiyah--Hitchin--Singer theorem of SU(2)-instantons on the 4-sphere.
Thesis Advisor: Mike Miller Eismeier, Columbia University
This thesis was awarded the John Dash Van Buren Jr. Prize in Mathematics by Columbia University for being the best undergraduate thesis submitted in 2023.
Rair Macêdo, Arjun S. Kudinoor, Karen L. Livesey, Robert E. Camley
Rair Macêdo, Arjun S. Kudinoor, Karen L. Livesey, Robert E. Camley
The consequences of non-uniform exchange in magnetic systems are reported. A linearly varying exchange interaction is used along a magnetic strip as a route to spatial inversion symmetry-breaking. It is found that, in addition to asymmetric modes and localization, spatially varying exchange can be used to design nonreciprocal magnetic signal excitation at frequencies that are tunable.
Research Mentor: Robert Camley, University of Colorado at Colorado Springs
Blogs
Blogs
October 8, 2025
October 8, 2025
In the 2025 Physics Nobel Prize press release, the very first opportunity listed for the next generation of quantum technologies is quantum cryptography, followed by quantum computers and quantum sensors. In this blog, I share a brief history of quantum computers and Shor's algorithm. I then explain how Shor's algorithm poses a threat to modern asymmetric encryption. Finally, I emphasize the need to secure our data from future quantum attacks using post-quantum cryptography.
August 19, 2025
August 19, 2025
In the era of AI, data doesn’t just grow—it evolves. Together with Protegrity’s CEO, Michael Howard, I explore how businesses can survive and thrive by adopting a Darwin–Pareto mindset.
✅ See your company as a point in a multi-objective space — cost, quality, CX, innovation, etc.
✅ Continuously rebalance trade-offs to move closer to the Pareto frontier.
✅ Build “first-class” data, which is proprietary, shareable, and protected.
This isn’t about encrypting for compliance—it’s about creating data that hyperscalers don’t have, that circulates safely across systems, and that powers AI with privacy at its core.
Just For Fun
Just For Fun
Theoretical Physics
Theoretical Physics
October 27, 2024
October 27, 2024
A translation between the partition function of a canonical ensemble in thermal equilibrium and the partition function of an ensemble of quantum mechanical fields using a path integral formulation of quantum mechanics. An application to deriving the Hawking temperature of black holes is described.
Spring 2023 - PHYS 3500 Independent Readings in Supersymmetry and AdS/CFT
Spring 2023 - PHYS 3500 Independent Readings in Supersymmetry and AdS/CFT
A formulation of supersymmetric quantum mechanics and the Witten index. Relations between the Atiyah-Singer index theorem for chiral operators and the Witten index for N=1 supersymmetric nonlinear sigma model are discussed.
Fall 2021 - MATH 4051 Topology
Fall 2021 - MATH 4051 Topology
A study of Banach spaces, Hilbert spaces, and C* Algebras. The Dirac von-Neumann and Hilbert space formulations of Quantum Mechanics are described and related.
Quantum Information
Quantum Information
Fall 2023 - PHYS 3081 Intermediate Physics Laboratory
Fall 2023 - PHYS 3081 Intermediate Physics Laboratory
An experimental demonstration of violating the CHSH-Bell Inequality using entangled photons. I was lucky to conduct this experiment as the 2022 Nobel Prize was awarded to Aspect, Clauser, and Zeilinger for their work on photon entanglement experiments.
Spring 2022 - PHYS 6038 Quantum Mechanics II
Spring 2022 - PHYS 6038 Quantum Mechanics II
A lecture on the variational principle, perturbation theory, and a simple example of the variational quantum eigensolver on Qiskit.
Summer 2021 - PHYS 3084 Quantum Simulation and Computing
Summer 2021 - PHYS 3084 Quantum Simulation and Computing
Formulation of a protocol to teleport an arbitrary n-qubit state using a 2n-qubit binary-inspired intermediary channel-state. The protocol was encoded on Qiskit and tested on IBM's qasm_simulator and quantum hardware.
Mathematics
Mathematics
Fall 2021 - MATH 4081 Differentiable Manifolds
Fall 2021 - MATH 4081 Differentiable Manifolds
Formulation and proof of the Fundamental Theorem of Riemannian Geometry. Includes a study of Affine connections, Riemannian connections, and Riemannian manifolds
Fall 2021 - MATH 4042 Modern Algebra
Fall 2021 - MATH 4042 Modern Algebra
A study of quaternions, quaternion algebras, and biquaternions
Miscellaneous Obsessions
Miscellaneous Obsessions
One can calculate geometric series without needing to use algebra or calculus. Instead, an understanding of game show taxes will suffice. This article demonstrates how this is the case.
An exploration of different scales of story points, and a focus on the Fibonacci scale and its connection to the golden ratio
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