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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220406T103000
DTEND;TZID=America/New_York:20220406T120000
DTSTAMP:20260620T071940
CREATED:20240214T102826Z
LAST-MODIFIED:20240301T064048Z
UID:10002671-1649241000-1649246400@cmsa.fas.harvard.edu
SUMMARY:Late time von Neumann entropy and measurement-induced phase transition
DESCRIPTION:Youtube Video \n  \nAbstract: Characterizing many-body entanglement is one of the most important problems in quantum physics. We present our studies on the steady state von Neumann entropy and its transition in Brownian SYK models. For unitary evolution\, we show that the correlations between different replicas account for the Page curve at late time\, and a permutation group structure emerges in the large-N calculation. In the presence of measurements\, we find a transition of von Neumann entropy from volume-law to area-law by increasing the measurement rate. We show that a proper replica limit can be taken\, which shows that the transition occurs at the point of replica symmetry breaking.
URL:https://cmsa.fas.harvard.edu/event/4-6-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-04.06.2022-1583x2048-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220407T093000
DTEND;TZID=America/New_York:20220407T110000
DTSTAMP:20260620T071940
CREATED:20240214T102601Z
LAST-MODIFIED:20240301T063834Z
UID:10002669-1649323800-1649329200@cmsa.fas.harvard.edu
SUMMARY:Lattice Gauge Theory View of Toric Codes\, X-cube\, and More
DESCRIPTION:Youtube Video \n  \nAbstract: Exactly solvable spin models such as toric codes and X-cube model have heightened our understanding of spin liquids and topological matter in two and three dimensions. Their exact solvability\, it turns out\, is rooted in the existence of commuting generators in their parent lattice gauge theory (LGT). We can understand the toric codes as Higgsed descendants of the rank-1 U(1) LGT in two and three dimensions\, and the X-cube model as that of rank-2 U(1) LGT in three dimensions. Furthermore\, the transformation properties of the gauge fields in the respective LGT is responsible for\, and nearly determines the structure of the effective field theory (EFT) of the accompanying matter fields. We show how to construct the EFT of e and m particles in the toric codes and of fractons and lineons in the X-cube model by following such an idea. Recently we proposed some stabilizer Hamiltonians termed rank-2 toric code (R2TC) and F3 model (3D). We will explain what they are\, and construct their EFTs using the gauge principle as guidance. The resulting field theory of the matter fields are usually highly interacting and exhibit unusual conservation laws. Especially for the R2TC\, we demonstrate the existence of what we call the “dipolar braiding statistics” and outline the accompanying field theory which differs from the usual BF field theory of anyon braiding. \nReferences:\n[1] “Model for fractions\, fluxons\, and free verte excitations”\, JT Kim\, JH Han\, Phys. Rev. B 104\, 115128 (2021)\n[1] “Rank-2 toric code in two dimensions”\, YT Oh\, JT Kim\, EG Moon\, JH Han\, Phys. Rev. B 105\, 045128 (2022)\n[2] “Effective field theory for the exactly solvable stabilizer spin models”\, JT Kim\, YT Oh\, JH Han\, in preparation.\n[3] “Effective field theory of dipolar braiding statistics in two dimensions”\, YT Oh\, JT Kim\, JH Han\, in preparation.
URL:https://cmsa.fas.harvard.edu/event/4-7-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-04.07.2022-1583x2048-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220413T203000
DTEND;TZID=America/New_York:20220413T220000
DTSTAMP:20260620T071940
CREATED:20240214T102340Z
LAST-MODIFIED:20240301T063645Z
UID:10002668-1649881800-1649887200@cmsa.fas.harvard.edu
SUMMARY:Why is the mission impossible? Decoupling the mirror Ginsparg-Wilson fermions in the lattice models for two-dimensional abelian chiral gauge theories
DESCRIPTION:Youtube Video \nAbstract: It has been known that the four-dimensional abelian chiral gauge theories of an anomaly-free set of Wely fermions can be formulated on the lattice preserving the exact gauge invariance and the required locality property in the framework of the Ginsparg- Wilson relation. This holds true in two dimensions. However\, in the related formulation including the mirror Ginsparg-Wilson fermions\, it has been argued that the mirror fermions do not decouple: in the 3450 model with Dirac- and Majorana-Yukawa couplings to XY-spin field\, the two- point vertex function of the (external) gauge field in the mirror sector shows a singular non-local behavior in the so-called ParaMagnetic Strong-coupling(PMS) phase. \nWe re-examine why the attempt seems a “Mission: Impossible” in the 3450 model. We point out that the effective operators to break the fermion number symmetries (’t Hooft operators plus others) in the mirror sector do not have sufficiently strong couplings even in the limit of large Majorana-Yukawa couplings. We also observe that the type of Majorana-Yukawa term considered there is singular in the large limit due to the nature of the chiral projection of the Ginsparg-Wilson fermions\, but a slight modification without such singularity is allowed by virtue of the very nature. \nWe then consider a simpler four-flavor axial gauge model\, the 14(-1)4 model\, in which the U(1)A gauge and Spin(6)( SU(4)) global symmetries prohibit the bilinear terms\, but allow the quartic terms to break all the other continuous mirror-fermion symmetries. This model in the weak gauge-coupling limit is related to the eight-flavor Majorana Chain with a reduced SO(6)xSO(2) symmetry in Euclidean path-integral formulation. We formulate the model so that it is well-behaved and simplified in the strong-coupling limit of the quartic operators. Through Monte-Carlo simulations in the weak gauge-coupling limit\, we show a numerical evidence that the two-point vertex function of the gauge field in the mirror sector shows a regular local behavior. \nFinally\, by gauging a U(1) subgroup of the U(1)A× Spin(6)(SU(4)) of the previous model\, we formulate the 21(−1)3 chiral gauge model and argue that the induced effective action in the mirror sector satisfies the required locality property. This gives us “A New Hope” for the mission to be accomplished.
URL:https://cmsa.fas.harvard.edu/event/4-13-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-04.13.22-1583x2048-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220414T093000
DTEND;TZID=America/New_York:20220414T110000
DTSTAMP:20260620T071940
CREATED:20240214T102053Z
LAST-MODIFIED:20240813T162915Z
UID:10002666-1649928600-1649934000@cmsa.fas.harvard.edu
SUMMARY:Cancellation of the vacuum energy and Weyl anomaly in the standard model\, and a two-sheeted\, CPT-symmetric universe
DESCRIPTION:Youtube video \n  \n\n\nAbstract: I will explain a mechanism to cancel the vacuum energy and both terms in the Weyl anomaly in the standard model of particle physics\, using conformally-coupled dimension-zero scalar fields.  Remarkably\, given the standard model gauge group SU(3)xSU(2)xU(1)\, the cancellation requires precisely 48 Weyl spinors — i.e. three generations of standard model fermions\, including right-handed neutrinos.  Moreover\, the scalars possess a scale-invariant power spectrum\, suggesting a new explanation for the observed primordial density perturbations in cosmology (without the need for inflation). \nAs context\, I will also introduce a related cosmological picture in which this cancellation mechanism plays an essential role.  Our universe seems to be dominated by radiation at early times\, and positive vacuum energy at late times.  Taking the symmetry and analyticity properties of such a universe seriously suggests a picture in which spacetime has two sheets\, related by a symmetry that\, in turn\, selects a preferred (CPT-symmetric) vacuum state for the quantum fields that live on the spacetime.  This line of thought suggests new explanations for a number of observed properties of the universe\, including: its homogeneity\, isotropy and flatness; the arrow of time; several properties of the primordial perturbations; and the nature of dark matter (which\, in this picture\, is a right-handed neutrino\, radiated from the early universe like Hawking radiation from a black hole).  It also makes a number of testable predictions. \n(Based on recent\, and ongoing\, work with Neil Turok: arXiv:1803.08928\, arXiv:2109.06204\, arXiv:2110.06258\, arXiv:2201.07279.)
URL:https://cmsa.fas.harvard.edu/event/4-14-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-04.14.22-1583x2048-1-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220422T153000
DTEND;TZID=America/New_York:20220422T170000
DTSTAMP:20260620T071940
CREATED:20240214T101342Z
LAST-MODIFIED:20240229T112525Z
UID:10002662-1650641400-1650646800@cmsa.fas.harvard.edu
SUMMARY:Higgs = SPT
DESCRIPTION:Speaker: Ruben Verresen \nTitle: Higgs = SPT \nAbstract: The Higgs phase of a gauge theory is important to both fundamental physics (e.g.\, electroweak theory) as well as condensed matter systems (superconductors and other emergent phenomena). However\, such a charge condensate seems subtle and is sometimes described as the spontaneous breaking of gauge symmetry (or a global subgroup). In this talk\, I will argue that the Higgs phase is best understood as a symmetry-protected topological (SPT) phase. The concept of SPT phases arose out of the condensed matter community\, to describe systems with short-range entanglement and edge modes which cannot be removed in the presence of certain symmetries. The perspective that the Higgs phase is an SPT phase recovers known properties of the Higgs phase and provides new insights. In particular\, we revisit the Fradkin-Shenker model and the distinction between the Higgs and confined phases of a gauge theory.
URL:https://cmsa.fas.harvard.edu/event/4-22-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/jpeg:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-04.22.22-1583x2048-1.jpg
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220428T103000
DTEND;TZID=America/New_York:20220428T120000
DTSTAMP:20260620T071940
CREATED:20240214T101152Z
LAST-MODIFIED:20240229T112257Z
UID:10002661-1651141800-1651147200@cmsa.fas.harvard.edu
SUMMARY:Aspects of 4d supersymmetric dynamics and geometry
DESCRIPTION:Abstract: We will overview the program of geometrically engineering four dimensional supersymmetric QFTs as compactifications of six dimensional SCFTs. In particular we will discuss how strong coupling phenomena in four dimensions\, such as duality and emergence of symmetry\, can be better understood in such geometric constructions.
URL:https://cmsa.fas.harvard.edu/event/4-28-2022-quantum-matter-in-mathematics-and-physics/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-04.28.22-1583x2048-1.png
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