Nuclear and Particle Theory Seminar

Monday, February 6

Title: Flash Talks and Introductions for the term

Monday, February 13
Julian Urban, CTP

Title: From imaginary to real time via spectral reconstruction

Abstract: Non-perturbative approaches to strongly correlated quantum field theories are generally formulated in Euclidean spacetime and carried out via numerical calculations, granting access to equilibrium properties in the form of discrete correlation function data with finite uncertainty. Direct analytic continuation to Minkowski spacetime presents severe conceptual difficulties and the real-time physics information is strongly suppressed in the imaginary-time data. However, it may be accessed indirectly via the associated spectral functions, obtained by inverting the Källén-Lehmann integral representation. A powerful non-parametric ansatz for the probabilistic treatment of such heavily ill-conditioned linear inverse problems is Gaussian process regression. In this talk, I will introduce the general approach and present two applications: 1. The reconstruction of 2+1 flavor lattice QCD data for ghost and gluon propagators in the Landau gauge, as well as computing the strong coupling constant in the full complex momentum plane. 2. The extraction of glueball masses from timelike interaction channels of the four-gluon vertex in Yang-Mills theory, computed with the functional renormalization group. Finally, I will discuss potential improvements of the approach connecting it to a large body of research in machine learning and numerical optimization.

Monday, February 20

President’s Day. No Seminar.

Monday, February 27

Jessie Shelton, University of Illinois, Champaign-Urbana

Title: Looking for new physics in the late early universe

Abstract: Observations of the cosmic microwave background (CMB) and the light element abundances predicted by big bang nucleosynthesis (BBN) provide our earliest windows onto the evolution of our universe, and can provide powerful and often model-insensitive constraints on particle physics beyond the SM. I will discuss recent work using early universe observations to sharpen our understanding of the allowed particle physics of our universe, including updated BBN constraints on the number of effective relativistic degrees of freedom, N_eff. I will end with discussing an example class of models that can still cause substantial departures from standard cosmology between BBN and the CMB, which make interesting and unusual predictions for observables on soon-to-be-tested cosmological scales.


Monday, March 6

Robert Szafron, Brookhaven National Lab.

Title: Soft theorems in gravity from effective field theory

Abstract: The soft limits of gauge theories and perturbative gravity are surprisingly similar despite different gauge structures of both theories. However, unlike in gauge theories, collinear divergences do not manifest in gravity. Thus, it is worth exploring infra-red limits of gravity and gauge theories from the perspective of an effective field theory approach. In my talk, I will discuss the fundamental role of emergent gauge symmetries for soft-collinear gravity and their part in constraining the structure of the subleading soft theorems. I will use the effective field theory formalism to derive the subleading soft theorem, demonstrate its universal structure and discuss how power-counting restricts loop corrections in gravity.

Monday, March 13

Ross Young, University of Adelaide

Title: Compton amplitude and low moments of nucleon structure functions from lattice QCD

Abstract: The study of inclusive processes is an extremely powerful tool in the understanding of the fundamental properties of strongly-interacting matter — both as a probe of the underlying dynamics and interactions, and as an input to precision searches for physics beyond the standard model. As a first principles, non-perturbative tool for studying QCD, lattice QCD has however been challenged to compute inclusive rates outside of a limited kinematic domain. By studying the Compton amplitude of the nucleon, it is possible to overcome some of these limitations, and therefore open new opportunities for lattice QCD studies. Here I focus on recent results that have demonstrated power corrections in the low moments of the nucleon structure functions, including a first hint at revealing the longitudinal structure — something that has been considered unattainable from conventional approaches.


Monday, March 20

Yikun Wang, CalTech

Title: Axion Detection with Optomechanical Cavities

Abstract: In this talk, I will present our recent proposal of searching for axion dark matter with an optomechanical cavity filled with a material such as superfluid helium. Axion absorption converts a pump laser photon to a photon plus a phonon. The axion absorption rate is enhanced by the high occupation number of coherent photons or phonons in the cavity, allowing our proposal to largely overcome the extremely small axion coupling. The axion mass probed is set by the relative frequency of the photon produced in the final state and the Stokes mode. Because neither the axion mass nor momentum need to be matched to the physical size of the cavity, we can scale up the cavity size while maintaining access to a wide range of axion masses (up to a meV) complementary to other cavity proposals.


Monday, March 27

Spring Break. No Seminar

Monday, April 3

Claudia Ratti, University of Houston

Title: The equation of state of QCD: status and perspectives.
 
Abstract: Simulations of Quantum Chromodynamics, the theory of strong interactions, currently cannot be performed at finite density. Nevertheless, expansion methods allow us to access a portion of the finite-density region. I will review the state-of-the-art equation of state for strongly interacting matter from first principles. I will then discuss how to extend these calculations to larger density, approaching the relevant regime for neutron star mergers.


Monday, April 10

Alex Mitov, Cambridge University

Title: Extending the precision frontier for multijet production at the LHC

Abstract: The measurement of the 3-to-2 jet production ratio R3/2 at the LHC holds many promises and has been promoted for about a decade now. Yet the insufficient precision until now of the relevant theory predictions prevented its effective use. I’ll present the first NNLO QCD calculation of 3-jet production at the LHC and one of its first LHC applications: the ATLAS measurement of the running of the strong coupling constant through TeV energies. Lessons in NNLO (and higher) order calculations will be emphasized, like the realization there are currently two bottlenecks: the first one is the availability of 2-loop amplitudes. The second one is how to make such calculations accessible and useful for everyone. I will present a novel approach, called HighTEA, which aims at resolving the second bottleneck.

Monday, April 17

Patriots Day. No Seminar.

Monday, April 24

Quentin Bonnefoy, University of California, Berkeley

Title: A colorful mirror solution to the strong CP problem

Abstract:  I will discuss the strong CP problem, i.e. the unexplained absence of CP violation mediated by strong interactions. I will first argue that solving that problem is a nightmare for bottom-up theorists, through the discussion of the axion quality problem and of the renormalization of the QCD theta angle. I will then remind that the latter example lies at the heart of solutions to the strong CP problem which rely on spontaneously broken spacetime parity, and I will present a new model in that landscape (which remains quite unexplored). It is based on a complete mirror copy of the standard model, linked to our world by colored portal fields. Those induce the partial spontaneous breaking of the color groups and yield a vanishing theta angle at low energies. The lightest BSM fields could be colored (pseudo-Goldstone or vector) bosons.

Monday, May 1

Govert Nijs, CTP

Title: Nuclear Structure and Heavy Ion Collisions

Abstract: Studies of heavy ion collisions have traditionally focused mostly on
the hydrodynamic expansion of the quark-gluon plasma created in the
collision and the far-from-equilibrium dynamics preceding it. Recently,
several studies have started to look into the shapes of the colliding
nuclei themselves just prior to the collision and how they affect the
shapes. In this talk, I will discuss three of these studies, where the
most recent one contains the first Bayesian inference of the neutron
skin of Pb-208 from LHC data, the result of which is relevant for the
study of neutron stars.

Monday, May 8

Ian Moult, Yale University

Title: Imaging the Intrinsic and Emergent Scales of QCD with Colliders

Abstract: The most powerful means of exploring nature at small length scales is through the use of particle colliders. Colliders smash particles together at high energies, briefly producing new particles through quantum fluctuations, which then decay into complicated sprays of energy in surrounding detectors. Much in analogy with how the details of our cosmic history are imprinted in the cosmic microwave background, the detailed features of the interactions of elementary particles are imprinted into macroscopic correlations in the energy flow of the collision products. Understanding the underlying microscopic physics in collider experiments therefore relies on our ability to decode these complicated correlations in energy flow. In turn, the desire to understand how to compute collider observables from an underlying quantum field theory (QFT) description has been a driver of theoretical developments and insights into the structure of QFT itself.


In this talk I will present some recent highlights in the quest to better understand the strong nuclear force at collider experiments, driven by recent theoretical developments in the understanding of a class of observables called “Energy Correlators”.  I will then apply these developments to explore a variety of interesting phenomena in QCD, ranging from weighing the heaviest quark, to imaging the most perfect fluid.


Monday, May 15

Volodymyr Vovchenko, University of Houston

Title: Probing the QCD phase structure with fluctuations in heavy-ion collisions

Abstract: The phase structure of QCD and the nature of the transition between ordinary hadronic matter and the deconfined state of quark-gluon plasma remain among the key open questions in high-energy physics. This talk will explore how these questions can be addressed using fluctuation observables, with a focus on event-by-event fluctuations in heavy-ion collisions and the search for the QCD critical point at finite baryon number density. I will discuss the dynamical description of proton number cumulants in heavy-ion collisions based on relativistic hydrodynamics, and the resulting constraints on the QCD critical point derived from recent data from the RHIC beam energy scan.

Thursday, June 1 @ 1:30 (NOTE SPECIAL DAY)

Ben Safdi, U. California, Berkeley

Title: Novel Astrophysical Probes of Axions

Abstract: The QCD axion and ultra-light axion like particles are well motived extensions to the Standard Model that could solve the strong CP problem related to the neutron electric dipole moment and explain the dark matter of the Universe.  Moreover, as I will review, they naturally arise in the context of string theory compactifications with couplings to matter slightly below current upper limits. Improving the sensitivity to ultra-light axions that do not contribute a sizable fraction of the dark matter requires novel astrophysical probes, as such particles are too weakly interacting to be explored purely with laboratory techniques.  I will discuss recent methods that my group has developed that constrain ultra-light axions, including white dwarf polarization probes and neutron star cooling analyses, and I will comment on more speculative future approaches. I will then summarize the near-term outlook for detecting ultra-light axions at couplings below current upper limits.​

Fall 2022

Monday, September 12
Sokratis Trifinopoulos, MIT, IAIFI

Title: New Physics in b →s μμ: FCC-hh or a Muon Collider?​

Abstract: Rare flavour-changing neutral-current transitions b→sμ⁺μ⁻ probe higher energy scales than what is directly accessible at the LHC. Therefore, the presence of new physics in such transitions, as suggested by the present-day LHCb anomalies, would have a major impact on the motivation and planning of future high-energy colliders. The two most prominent options currently debated are a proton-proton collider at 100 TeV (FCC-hh) and a multi-TeV muon collider (MuC). In this work, we compare the discovery prospects at these colliders on benchmark new physics models indirectly detectable in b→sμ⁺μ⁻ decays but beyond the reach of the high-pT  searches at the HL-LHC. We consider a comprehensive set of scenarios: semileptonic contact interactions, Z′ from a gauged U(1)_{B 3 − L μ} and U(1)_{L μ − L τ}, the scalar leptoquark S₃, and the vector leptoquark U₁. We find that a 3 TeV MuC has a sensitivity reach comparable to the one of the FCC-hh. However, for a heavy enough mediator, the new physics effects at a 3 TeV MuC are only observed indirectly via deviations in the highest energy bin, while the FCC-hh has a greater potential for the discovery of a resonance. Finally, to completely cover the parameter space suggested by the bsμμ anomalies, among the proposed future colliders, only a MuC of 10 TeV (or higher) can meet the challenge.​


Monday, September 19
Kyle Lee, MIT, CTP

Title: Conformal Colliders Meet the LHC

Abstract: Reframing jet substructures in terms of multipoint correlation functions of energy flow light-ray operators offers new means to study the dynamics of QCD jets, providing many interesting phenomenological applications (including QCD fragmentation, track functions, precision measurements, and more) and allowing applications of theoretical developments in the study of conformal field theories.
 
In order to fully benefit from such a reframing based on energy correlators, it is imperative to develop a theoretical framework to incorporate the complicated initial state of the LHC, which goes beyond what has previously been considered in theoretical studies of energy correlators. 
 
In this talk, I will present a theoretical framework developed using SCET to study energy correlators at the LHC, allowing recent calculations of energy correlators to be seamlessly embedded in the complicated LHC environment.
 
Using this approach, I will present results for the scaling behavior of multipoint energy correlators and compare with CMS Open Data, opening the door to the quantitative study of energy correlators at the LHC.
 
Additionally, we extend existing factorization theorems to include the mass of heavy quarks. Using this framework, we then observe a clear transition from the scaling region to the region corresponding to the heavy quark mass scale, manifesting the long-sought-after dead-cone effect and illustrating fundamental effects and illustrating fundamental effects coming from the intrinsic mass of beauty and charm quarks before they are confined inside hadrons.


Monday, September 26
Masaaki Tomii, University of Connecticut

Title: $K \to \pi\pi$ decay on the lattice with periodic boundary conditions

Abstract: Since RBC/UKQCD’s latest publication of lattice result for direct CP violation and the Delta I = 1/2 rule in $K \to \pi\pi$ decay, which was made with G-parity boundary conditions in 2020, we have been revisiting this problem with a different lattice setup with periodic boundary conditions and multiple lattice spacings to see the consistency with our previous result and to improve the precision.  While there was an expectation that it could be difficult to extract physical kinematics of K to pipi decay with periodic boundary conditions, we overcome it through the variational method.  Also periodic boundary conditions provide a relatively easy way to introduce electromagnetic and isospin breaking corrections, which is desired to be implemented in near future.  In this talk, we show our preliminary result and discuss prospect of high-precision calculation of $K \to \pi\pi$ decay with periodic boundary conditions.


Monday, October 3
Fernando Romero Lopez MIT, CTP
Title: Hadronic resonances from lattice QCD

Abstract: Most of the known hadrons in the low-energy QCD spectrum correspond to resonances that are found in multi-particle scattering processes. Indeed, lattice QCD can be used to perform first-principles calculations of scattering amplitudes, and so, the properties such as the mass and width of hadronic resonances can be computed. In this talk, I will review recent progress on the study of some resonances from lattice QCD. In particular, I will focus on meson-baryon resonances, such as the Delta(1232) resonance, and the study of a three-body resonance in a toy model.

Monday, October 10
Indigenous People’s Day (No Seminar)

Monday, October 17
Lena Funcke, MIT, CTP
Title: Quantum Algorithms for Particle Physics

Abstract: In this talk, I will review recent advances in applying quantum computing to particle physics. Quantum technology offers the prospect to efficiently simulate sign-problem afflicted regimes in lattice field theory, such as the presence of topological terms, chemical potentials, and out-of-equilibrium dynamics. Moreover, quantum computing can be applied to quadratic unconstrained binary optimization (QUBO) problems in collider physics. The path towards quantum simulations of (3+1)D particle physics requires many incremental steps, including algorithmic development, hardware improvement, methods for circuit design, as well as error mitigation and correction techniques. After reviewing these requirements and recent developments, I will discuss the main challenges and future directions.

Monday, October 24
Seth Koren, University of Chicago
Title: Discrete Gauged B-L and the Cosmological Lithium Problem

Abstract: We study the baryon minus lepton number gauge theory broken by a scalar with charge six. The infrared discrete vestige of the gauge symmetry demands the existence of cosmic string solutions, and their production as dynamical objects in the early universe is guaranteed by causality. These topological defects can support interactions which convert three protons into three positrons, and we argue an `electric’-`magnetic’ interplay can lead to an amplified, strong-scale cross-section in an analogue of the Callan-Rubakov effect.

The cosmological lithium problem—that theory predicts a primordial abundance far higher than that observed—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We suggest cosmic strings have disintegrated O(1) of the primordial lithium nuclei and estimate the rate in a benchmark scenario. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after Big Bang Nucleosynthesis.

Monday, October 31
Harikrishnan Ramani, Stanford University

Title: Dark matter detection with trapped ions

Abstract: Axion Dark Matter, Dark Photon Dark matter and Millicharged particle dark matter are some of the simplest and popular models of dark matter and are looked for in various experiments. Yet, there continue to exist inaccessible regions in interaction and mass parameter space for these models. In this talk I propose a new way to detect the tiny electric fields produced by these dark matter candidates: the remarkably stable trapped ions, tools developed in the context of quantum metrology and quantum computing. I present preliminary data from pilot experiments as well as steps to improve sensitivity in the future.

Based on: https://arxiv.org/abs/2208.06519, https://arxiv.org/abs/2108.05283. 

Monday, November 7
No seminar this week.

Monday, November 14
Christina Gao, University of Illinois, Champaigne-Urbana
Title: Axion wind detection with the homogeneous precession domain of superfluid helium-3

Abstract: Axions and axion-like particles may couple to nuclear spins like a weak oscillating effective magnetic field. Existing proposals for detecting this “axion wind” sourced by dark matter exploit analogies to nuclear magnetic resonance (NMR) and aim to detect the small transverse field generated when the axion wind resonantly tips the precessing spins in a polarized sample of material. We describe a new proposal using the homogeneous precession domain (HPD) of superfluid 3He as the detection medium, where the effect of the axion wind is a small shift in the precession frequency of a large-amplitude NMR signal. We argue that this setup can provide broadband detection of multiple axion masses simultaneously, and has competitive sensitivity to other axion wind experiments such as CASPEr-Wind at masses below 10−7 eV by exploiting precision frequency metrology in the readout stage.


Monday, November 21
Jean-Francois Paquet, Vanderbilt University

Title: Nuclear collisions as seen through photons

Abstract: The energy spectrum of photons is understood well in ultrarelativistic collisions of protons or of nuclei, as long as the photons’ energy reaches the 10+ GeV range. For lower energy photons, however, considerable differences appear between the collisions of protons and of nuclei. In the heavy ion case, the production of GeV-energy photons appears to be dominated by electromagnetic radiation from the plasma of deconfined nuclear matter produced in the collisions. I will discuss the status of theoretical calculations of the photon energy spectrum in proton-proton and heavy-ion collisions, reviewing the current agreement with experimental data, as well as recent developments.

Monday, November 28
Wilke van der Schee, CERN

Title: Heavy ion collisions and the shape of nucleons and nuclei

Abstract: In this seminar I will give a brief introduction to the formation of quark-gluon plasma (QGP) in heavy ion collisions. This consists of an initial colliding stage, a hydrodynamic stage and a hadronic gas phase after which particles can finally be observed. While there is nowadays a wealth of experimental data, it is challenging to infer conclusions on specific aspects and I will highlight a recent effort that in particular constrains the nucleon width inside a nucleus. Finally, given the current precision of heavy ion experiments I will give examples of how these are sensitive to the shape of nuclei.



Monday, December 5
Carolyn Raithel, IAS

Title: Probing Dense Matter with Gravitational Waves
 
Abstract: Neutron star mergers provide a unique probe of the dense matter equation of state (EOS) across a wide range of parameter space, from the cold and equilibrated matter of the inspiral, to the shock-heated and higher-density conditions that govern the post-merger evolution. In this talk, I will start with an overview of what we have learned about the EOS so far from the first LIGO-Virgo observations of binary neutron star inspirals. I will then introduce a new category of “doppelgänger” EOS models, which produce the same gravitational wave signatures despite significant differences in the underlying EOS, and I will discuss the prospects for resolving this new observational degeneracy. In the second part of the talk, I will present a series of neutron star merger simulations that employ a phenomenological framework for studying new parts of the EOS parameter space. I will use these simulations to discuss what additional constraints we may be able to extract from a future detection of gravitational waves emitted the remnant neutron star that forms after a merger.




Spring 2022


January 31, 2022
Mikhail Ivanov, IAS

Title: Love and Naturalness
Abstract: It has been known for a decade that black holes are the most rigid objects in the universe: their tidal deformations (Love numbers) vanish identically in general relativity in four dimensions. This has represented a naturalness problem in the context of classical worldline effective field theory. In my talk I will present a new symmetry of general relativity (Love symmetry) that resolves this naturalness paradox. I will show that perturbations of rotating black holes enjoy an SL(2,R) symmetry in the suitable defined near zone approximation. This symmetry, while approximate in general, in fact yields exact results about static tidal deformations. This symmetry also implies that generic regular black hole perturbations form infinite-dimensional SL(2,R) representations, and in some special cases these are highest weight representations. It is the structure of these highest weight representations that forces the Love numbers to vanish. All other facts about Love numbers also acquire an elegant explanation in terms of SL(2,R) representation theory. 

February 7, 2022
TBA

February 14, 2022
Isabel Garcia Garcia, University of California, Santa Barbara
TBA

February 21, President’s Day Holiday No Seminar

February 28, 2022
Siddharth Mishra-Sharma
Title: Dark photon oscillations in our inhomogeneous Universe and their imprint on CMB, radio, and 21-cm observations
Abstract: Kinetically-mixed dark photons can oscillate to Standard Model photons, and vice versa. These oscillations can be resonantly enhanced when the plasma mass of the Standard Model photon, which tracks the cosmic electron number density, matches the dark photon mass. I will present an analytic formalism for computing the effect of dark photon oscillations taking into account inhomogeneities in the plasma mass in our Universe and use this to derive new bounds on ultralight dark photons from spectral distortions of the CMB. I will then discuss how dark photon-to-photon oscillations could imprint themselves on observations of the redshifted 21-cm hydrogen line. Finally, I will motivate a possible connection to the long-standing radio background excess measured by ARCADE and low-frequency radio observations.

March 7, 2022
Clara Murgui, CalTech
“DarkUnification: a UV complete theory for asymmetric dark matter”.
Abstract: Motivated by the observed ratio of dark matter to baryon mass densities, which is around a factor 5, we propose a theory of dark-color unification. In this theory, the dark to visible baryon masses are fixed by the ratio of dark to visible confinement scales, which are determined to be nearby in mass through the unification of the dark and visible gauge theories at a high scale. Together with a mechanism for darko-baryo-genesis, which arises naturally from the grand unification sector, the mass densities of the two sectors must be nearby, explaining the observed mass density of dark matter. We focus on the simplest possible example of such a theory, where Standard Model color SU(3)c is unified with dark color SU(2)D into SU(5) at an intermediate scale of around 10^8 -10^9 GeV. The dark baryon consists of two dark quarks in an isotriplet configuration. There are a range of important cosmological, astrophysical and collider signatures to explore, including dark matter self-interactions, early matter domination from the dark hadrons, gravitational wave signatures from the hidden sector phase transition, contributions to flavor observables, as well as Hidden Valley-like signatures at colliders.

March 14, 2022
Alessandro Lovato, ANL
Quantum Monte Carlo calculations of atomic nuclei and infinite neutron matter
Abstract
Understanding how the structure and dynamics of nuclei and infinite nuclear matter emerge from the individual interactions between neutrons and protons is a long-standing goal of nuclear theory. Solving the many-body Schrödinger equation involves non-trivial difficulties due to the non-perturbative nature and spin-isospin dependence of nuclear forces. Quantum Monte Carlo methods tackle this problem using stochastic techniques and accurately model short- and long-range nuclear dynamics. In this talk, I will present our recent calculations of the electroweak responses of atomic nuclei and matrix elements relevant to neutrino-less double-beta decay searches. I will then discuss the equation of state of infinite neutron matter, as obtained from local, chiral interactions that explicitly account for the excitation of the Delta resonance. Finally, I will provide some prospects on using artificial neural networks to compactly represent the wave functions of atomic nuclei and translational-invariant systems. 

March 21, 2022 Spring Break (no seminar)

March 28, 2022
Francesca Cuteri, University of Frankfurt
Lattice insight into the QCD phase diagram at zero and nonzero (isopin) density

April 4, 2022
Aditya Pathak, University of Manchester
 “A new paradigm for precision top mass measurement: Weighing the top with energy correlators”

April 11, 2022
Peter Denton, BNL
Light Dark Matter and Black Holes

April 18,2022 Patriot’s Day (no seminar)

April 25, 2022
Nobuo Sato, JLAB
The Next generation of QCD global analysis

May 2, 2022
Jamie Karthein, MIT
“Characterizing the Transition Region of the QCD Phase Diagram.”

May 9, 2022
Adrien Florio, Stony Brook
Dynamics of the O(4) critical point in QCD