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Theory Seminar

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

Chaotic and Thermal Aspects in the String S-Matrix

We compute tree level scattering amplitudes involving more than one highly excited states in bosonic string theory. We use these amplitudes to understand chaotic and thermal aspects of the excited string states lending support to the Susskind-Horowitz- Polchinski correspondence principle. The unaveraged amplitudes exhibit chaos in the resonance distribution as a function of kinematic parameters, which can be described by random matrix theory. Upon coarse-graining these amplitudes exponentiate, and give certain thermal indications.

Date:
Location:
CP 179
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Critical Phenomena and the Percolation Conduction Problem

The percolation problem describes the statistical properties of a lattice from which a fraction p of the bonds has been removed at random.   There is a critical value p_c such that there is long ranged connectedness for p > p_c and only finite sized clusters for p < p_c.    The percolation problem and its generalization, the percolation conduction problem, have phenomenology similar to "classical" critical phenomena, even though they are not described by thermodynamics.   I'll explain the connections, and go on to show how the resistance from an internal point to the boundary of a square  containing a percolating network at p_c can be explained using ideas from critical phenomena and conformal field theory. 
 

Date:
Location:
CP 303
Event Series:

Non-invertible symmetries, leptons, quarks, and why multiple generations

Generalized global symmetries are present in theories of particle physics, and understanding their structure can give insight into these theories and UV completions thereof.  We will particularly discuss the use of non-invertible chiral symmetries in BSM model-building. The identification of a non-invertible symmetry in Z' models of L_µ - L_τ reveals the existence of non-Abelian horizontal gauge theories which naturally produce exponentially small Dirac neutrino masses. Next we will uncover a subtler non-invertible symmetry in horizontal gauge theories of the quark sector which will lead us to a massless down-type quarks solution to strong CP in color-flavor unification. Intriguingly, this symmetry is present by virtue of the SM having the same numbers of colors and generations.

Date:
Location:
CP 179
Event Series:

Bootstrapping gauge theories

In this talk I will consider asymptotically free gauge theories with gauge group $SU(N_c)$ and $N_f$ quarks with mass $m_q <<\Lambda_{QCD}$ that undergo chiral symmetry breaking and confinement. I will described a proposal for a bootstrap method to compute the S-matrix of the pseudo-Goldstone bosons (pions) that dominate the low energy physics. For the important case of $N_c=3$, $N_f=2$, a numerical implementation of the method gives the phase shifts of the $S0$, $P1$ and $S2$ waves in good agreement with experimental results. The method incorporates gauge theory information ($N_c$, $N_f$, $m_q$, $\Lambda_{QCD}$) by using the form-factor bootstrap recently proposed by Karateev, Kuhn and Penedones together with a finite energy version of the SVZ sum rules. This requires, in addition, the values of the quark and gluon condensates. At low energy we impose constraints from chiral symmetry breaking which additionally require knowing the pion mass $m_\pi$.

Date:
Location:
CP 179
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Nonrelativistic Bound States with Effective Field Theories

Nonrelativistic bound states lie at the core of quantum physics,
permeating the fabric of nature across diverse realms, spanning particle
to nuclear physics, and from condensed matter to astrophysics. These
systems are pivotal in addressing contemporary challenges at the forefront
of particle physics. Characterized by distinct energy scales, they serve
as unique probes of complex environments. Historically, their
incorporation into quantum field theory was fraught with difficulty until
the emergence of nonrelativistic effective field theories (NREFTs).

In this talk, we delve into the construction of a potential NREFT
(pNREFT), a framework that directly tackles bound state dynamics
reimagining quantum mechanics from field theory.
Focusing on heavy quarkonia, pNRQCD facilitates systematic definitions and
precise calculations for high-energy collider
observables. At the cutting edge, we investigate nonrelativistic bound
states in intricate environments, like the newly discovered exotics X, Y,
Z  above the strong decay threshold and the behavior in out-of-equilibrium
scenarios, such as quarkonium suppression in a Quark Gluon Plasma or dark
matter interactions in the early universe.

Our ability to achieve precision calculations and control strongly
interacting systems is closely linked to bridging perturbative methods
with nonperturbative tools, notably numerical lattice gauge theories.

Date:
Location:
CP 179

Directions for Particle Physics Beyond Asymptotic Freedom

In recent years, new theories of particle physics have been discovered whose short-distance behaviour is controlled by an interacting (rather than a free) UV fixed point. The very existence of these asymptotically safe particle theories has opened up new directions to UV-complete the Standard Model of particle physics beyond the paradigm of asymptotic freedom. In this talk, I give a systematic overview of QCD-like theories with weakly and strongly coupled fixed points, with and w/o supersymmetry, and discuss key features. Concrete applications for BSM physics are also given. If time permits, I briefly outline how some of these ideas and insights are used to understand the quantisation of gravity.

 

Date:
Location:
CP 179 (Notice special date)

The Charm Mission into Flavor and BSM

The charm sector provides new and unique insights into flavor and BSM physics, complementing longstanding programs with kaons and B-mesons. We report status and  progress in null test searches from theory on rare decays of charm mesons and baryons into invisibles, photons and leptons, and where flavor experiments are currently pushing this frontier. We also discuss CP-violation together with sizable U-spin violation seen in hadronic 2-body decays at the LHCb-experiment. A stunning explanation of this puzzle is given by a light, hadrophilic Z-prime that can also resolve issues with the pion-form factor in J/psi-decays.
 

Date:
Location:
CP 179
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Theory/String Seminar: A fresh look at the large N limit of matrix models and holography

Abstract: We will discuss some known subtleties of emergent geometries from large N theories (why they are different from our normal expectation for a continuum spacetime) and discuss a way to address them. We will use matrix models as our main example. The primary tool will be an exact bosonization of nonrelativistic fermions that was discovered some time ago. 

Date:
Location:
CP 303

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
Event Series:

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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