Theory Seminar

Seminars are at 2pm in Room 179 CP Building unless otherwise indicated.

Probing Strong Nucleon-Nucleon Interactions at Short Distance

Among the four known fundamental forces or interactions, gravitation and electromagnetism are close to daily life, while the strong and weak forces only reveal themselves at sub-atomic or smaller scales. The strong force, which is mediated by gluon exchange between quarks confines quarks into protons and neutrons (nucleons). The residual component of this strong force that induces the strong nuclear interactions between nucleons at the fermi scale (10^-15m). This so-called "nuclear force" is attractive at a longer distance (e.g. for nucleon separation greater than the proton radius) and binds nucleons together into nuclei), while the force is strongly repulsive at a much shorter distance which prevents the nucleus from collapsing.  Nucleon interactions at short distances are not well-described in either QCD or the field theory. Experimentally, a series of electron-nucleon scattering measurements at Jefferson Lab (JLab) have determined about 20% of nucleons in heavy nuclei are moving fast (above the Fermi momentum) due to hard, short-distance interactions with another nucleons, forming so-called short-range correlated (SRC) pairs. Understanding those SRC pairs is necessary in providing a complete  description of nuclear structure. It also offers us a unique chance to probe the tensor and repulsive force at intermediate to short distances. In this talk, I will present recent results from the JLab Hall A tritium program which studied the momentum distribution, and spin/isospin structure of SRC pairs in the mirror nuclei tritium and helium-3. I will then discuss how those measurements help us better understand the short-distance part of strong nucleon-nucleon interactions, and their connections to future experiments.
Date:
Location:
Zoom
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Quantum Computing with Continuous Variables

NOTE SPECIAL TIME AND LOCATION

ABSTRACT: Quantum fields are fundamental constituents of the physical world. The encoding of quantum information in continuous-variable (CV) quantum fields, a.k.a. qumodes (in lieu of discrete-variable qubits), has enabled multipartite entanglement over millions of qumodes. This scale, unparalleled in any qubit architecture, defines new horizons and paradigms to be explored for quantum computing, quantum communication, and quantum sensing. I will outline our work in CV quantum computing applied to quantum field theory and quantum machine learning aiming at understanding properties of physical systems.

Date:
Location:
CP 303
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Effective Field Theories for precision beta decays

Beta decays have been instrumental in establishing the Standard Model as the theory of the electroweak interactions. In the era of the Large Hadron Collider, beta decays still provide very sensitive probes of physics beyond the Standard Model, which are highly competitive and complementary to searches at the energy frontier.For example, recent tensions in tests of the unitarity of the first row of the Cabibbo-Kobayashi-Maskawa quark mixing matrix might point to new physics at scales of about 10 TeV, still beyond the reach of the LHC.Because of the increasing experimental accuracy, advances in hadronic and nuclear theory are crucial to fully exploit beta decays as probes of new physics. In this talk, I will discuss the advantages of organizing various contributions to beta decays using effective field theories (EFTs). After discussing the EFT setup, I will review its application to neutron decay and to the calculation of the beta spectrum in the decay of 6He.
 
Date:
Location:
Zoom
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How are we saved from complete annihilation

Historically it was both a surprise and a theoretical triumph to find out that anti-matter exists at all. As we learnt more about the Universe, we are surprised by something very different - why do we almost exclusively see matter. The fact that throughout most of human history, we were oblivious to the existence of anti-matter is a testament to the dominance of matter over anti-matter. Looking at the earliest light and earliest elements in the Universe, we find that this imbalance goes back to at least when the Universe was a mere second old. However, inflation would wipe out any difference between matter and anti-matter and all processes we know of cannot create such an asymmetry. I will review the three main answers physicists have given to this fundamental question and what challenges face the community trying to shed light on this issue.
 
Date:
Location:
Zoom
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IR Phase of Thermal QCD, Non-Analytic Dirac Spectra and Emergent Dimensions

 Recent suggestion that SU(3) gauge theories with fundamental quarks generate a phase with IR scale invariant glue leads to interesting consequences materializing in very unusual ways. In this talk I will discuss these developments, including those featured in the Title.

Date:
Location:
Zoom
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(UV-complete) Emergent Matrix Cosmology

I will review recent results, and list outstanding challenges, of deriving an emergent spacetime from a non-perturbative proposal of String Theory -- namely, the BFSS matrix model. I will show how a metric can be coarse-grained from abstract matrix degrees of freedom, and how one naturally gets a scale-invariant spectrum of primordial perturbations in this model without introducing arbitrary tunable parameters. Furthermore, I will highlight distinct cosmological signatures of this model which have the potential of distinguishing it from other early-universe paradigms.
 

Date:
Location:
Zoom
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The Future of High Energy Theory with Quantum Computing

The advent of quantum computation presents the opportunity to solve questions in high energy theory which are inaccessible to classical computation such as real-time evolution and the equation of state at finite density. In order to take advantage of this new resource, a number of theoretical and computational hurdles will need to be addressed.  In this talk, I will discuss the state of the art research being performed in HEP and outstanding questions that require our attention going forward, focusing on digitization of lattice gauge theories and extracting physical results that demonstrate practical quantum advantage.

 

Date:
Location:
CP 179
Type of Event (for grouping events):

Muon g-2 with overlap valence fermions

The ~4σ discrepancy between the experiment and the data-driven theory prediction of the anomalous magnetic moment of the muon is one of the crucial benchmarks to verify the correctness of the standard model. On the lattice QCD side, the Budapest-Marseille-Wuppertal collaboration (BMWc) has a precise full calculation that favors the experimental prediction. Various independent lattice QCD calculations have been done to verify their findings, especially on well-defined ``window quantities'' which suffer fewer lattice artifacts. I will present our lattice calculation of the leading order (LO) hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment for the connected light and strange quarks in the widely used window t0 = 0.4 fm, t1 = 1.0 fm, ∆ = 0.15 fm, and also in the short distance region. We use the overlap fermions on 4 physical-point ensembles. Two 2+1 flavor RBC/UKQCD ensembles use the domain wall fermion (DWF) and Iwasaki gauge actions at a = 0.084 and 0.114 fm, and two 2+1+1 flavor MILC ensembles use the highly improved staggered quark (HISQ) and Symanzik gauge actions at a = 0.088 and 0.121 fm. They have incorporated infinite volume corrections from 3 additional DWF ensembles at L = 4.8, 6.4, and 9.6 fm and physical pion mass. Eventually, our results on the connected light and strange quarks in the widely used window agree with the BMWc findings and other most recent lattice calculations which deviate from the data-driven theory prediction.

Date:
Location:
Zoom
Type of Event (for grouping events):

The Status of the Cabibbo Angle Anomaly

Unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix is a measure 
of completeness of the Standard Model, and a good tool for looking for its extensions.
In the past few years there have been major new developments in the extraction 
of the CKM matrix elements Vud and Vus from the experimental data. At present, a 
3-sigma unitarity deficit is observed, known as the Cabibbo angle anomaly (CAA). 
I review the main ingredients of CAA across hadronic and nuclear-structure dependent 
radiative corrections, and give an outlook to future developments in theory and experiment.
Date:
Location:
Zoom (notice special time)
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A Path to Detecting Self-Interacting Dark Matter using Astrophysical Sub-Structure

Dark matter self interactions can leave distinctive signatures on the properties of satellite galaxies around Milky Way-like hosts. By analyzing a number of Milky Way dwarf galaxies, we were able to place new constraints on models of self-interacting dark matter which interact via a Yukawa potential. The results push the theory into a parameter space with a very specific prediction: self-interactions within satellite galaxies can be either very large (so large that new dynamical effects become important), or very small (so small that such models are usually thought of as collisionless), but not intermediate. Specifically, if self-interactions are large, some dwarfs of the Milky Way must be undergoing a process of gravothermal collapse, and this process has a number of distinct observational predictions which can be searched for in current and upcoming data.

Date:
Location:
Zoom
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