Theory Seminar

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

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
Type of Event (for grouping events):
Nonrelativistic Bound States with Effective Field Theories sgard2 Sat, 09/09/2023 - 10:17 am

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
Type of Event (for grouping events):
Directions for Particle Physics Beyond Asymptotic Freedom meides Wed, 09/06/2023 - 11:00 am
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)
Type of Event (for grouping events):

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
Type of Event (for grouping events):

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
Type of Event (for grouping events):

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
Type of Event (for grouping events):

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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