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SUMMARY:A proton radius puzzle update
DTSTART;VALUE=DATE-TIME:20201111T133000Z
DTEND;VALUE=DATE-TIME:20201111T150000Z
DTSTAMP;VALUE=DATE-TIME:20201129T215200Z
UID:indico-event-361@indico.knu.ac.kr
DESCRIPTION:Speakers: Carl E. Carlson (Jefferson Lab)\nWe shall discuss th
e newer theoretical and experimental results on the proton charge radius\,
along with some history for perspective. Although we will find that thing
s are looking more settled\, we will also talk about a few lingering probl
ems\, such as controversies involving data reanalysis\, whether the corres
ponding deuteron measurements themselves constitute a lingering problem\,
and ask whether the accuracy limitations of the two photon exchange calcul
ations are a barrier to future improvements in the accuracy of proton\, an
d also light nucleus\, radius measurements.\n\nWebinar at https://meet.jit
.si/ILCACseminar\n\n\n \nhttps://indico.knu.ac.kr/event/361/
LOCATION:
URL:https://indico.knu.ac.kr/event/361/
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BEGIN:VEVENT
SUMMARY:Comparing light-front quantization with instant-time quantization
DTSTART;VALUE=DATE-TIME:20201125T133000Z
DTEND;VALUE=DATE-TIME:20201125T150000Z
DTSTAMP;VALUE=DATE-TIME:20201129T215200Z
UID:indico-event-359@indico.knu.ac.kr
DESCRIPTION:Speakers: Philip D. Mannheim (University of Connecticut)\nIn t
his paper we compare light-front quantization and instant-time quantizatio
n both at the level of operators and at the level of their Feynman diagram
matrix elements. At the level of operators light-front quantization and i
nstant-time quantization lead to equal light-front time commutation (or an
ticommutation) relations that appear to be quite different from equal inst
ant-time commutation (or anticommutation) relations. Despite this we s
how that at unequal times instant-time and light-front commutation (or ant
icommutation) relations actually can be transformed into each other\, with
it only being the restriction to equal times that makes the commutation (
or anticommutation) relations appear to be so different. While our results
are valid for both bosons and fermions\, for fermions there are subtletie
s associated with tip of the light cone contributions that need to be take
n care of. At the level of Feynman diagrams we show for non-vacuum Feynman
diagrams that the pole terms in four-dimensional light-front Feynman diag
rams reproduce the widely used three-dimensional light-front on-shell Hami
ltonian Fock space formulation in which the light-front energy and light-f
ront momentum are on shell. Moreover\, we show that the contributions of p
ole terms in non-vacuum instant-time and non-vacuum light-front Feynman
diagrams are equal. However\, because of circle at infinity contributions
we show that this equivalence of pole terms fails for four-dimensional lig
ht-front vacuum tadpole diagrams. Then\, and precisely because of these ci
rcle at infinity contributions\, we show that light-front vacuum tadpole d
iagrams are not only nonzero\, they quite remarkably are actually equal to
the pure pole term instant-time vacuum tadpole diagrams. Light-front vacu
um diagrams are not correctly describable by the on-shell Hamiltonian form
alism\, and thus not by the closely related infinite momentum frame prescr
iption either. Thus for the light-front vacuum sector we must use the off-
shell Feynman formalism as it contains information that is not accessible
in the on-shell Hamiltonian Fock space approach. We show that light-front
quantization is intrinsically nonlocal\, and that for fermions this nonloc
ality is present in Ward identities. One can project fermion spinors into
so-called good and bad components\, and both of these components contribut
e in Ward identities. Central to our analysis is that the transformation
from instant-time coordinates and fields to light-front coordinates and f
ields is a unitary\, spacetime-dependent translation. Consequently\, not o
nly are instant-time quantization and light-front quantization equivalent\
, because of general coordinate invariance they are unitarily equivalent
.\n\n \n\narXiv:2005.00109\, to appear in Physics Reports\, https://doi.o
rg/10.1016/j.physrep.2020.09.001.\n\nWebinar at https://meet.jit.si/ILCACs
eminar\nhttps://indico.knu.ac.kr/event/359/
LOCATION:
URL:https://indico.knu.ac.kr/event/359/
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SUMMARY:Light-front wavefunctions\, covariant Bethe--Salpeter amplitudes\,
and meson elastic and transition form factors
DTSTART;VALUE=DATE-TIME:20201209T133000Z
DTEND;VALUE=DATE-TIME:20201209T150000Z
DTSTAMP;VALUE=DATE-TIME:20201129T215200Z
UID:indico-event-362@indico.knu.ac.kr
DESCRIPTION:Speakers: Pieter Maris (Iowa State University)\n\nBoth light-f
ront wavefunctions and covariant Bethe--Salpeter\namplitudes allow us to c
alculate a wide range of physical observables\;\nhowever\, neither the lig
ht-front wavefunctions nor the Bethe--Salpeter\namplitudes themselves are
physical observables\, and can therefore not\nbe measured directly. On th
e other hand\, both can be (and have been)\nused to evaluate e.g. meson el
astic and transition form factors\,\nthough the range in Q^2 over which on
e can unambiguously evalute such\nform factors without further assumptions
generally differs between\nlight-front approaches and the Bethe--Salpeter
aproach based on a\nEuclidean formulation.\n\nI will present recent resul
ts for meson light-front wavefunctions\,\nas well as physical observables
such as elastic and transition form\nfactors\, obtained in the Basis Light
-Front Quantization approach.\nI will also discuss explicitly covariant ca
lculations of meson elastic\nand transition form factors based on a Euclid
ean formulation of the\nDyson--Schwinger equations\, and highlight the (di
s)advantages of each\nof these two approach. Finally\, I will indicate ho
w one can in\nprinciple obtain the light-front wavefunction from the Bethe
--Salpeter\namplitudes using the Nakanishi integral representation\, and w
hat\nbottlenecks one might encounter in practice.\n\n \n\nWebinar at http
s://meet.jit.si/ILCACseminar\nhttps://indico.knu.ac.kr/event/362/
LOCATION:
URL:https://indico.knu.ac.kr/event/362/
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SUMMARY:Non-triviality of the vacuum in light-front quantization\; and imp
lications for correctly formulating light-front quantization
DTSTART;VALUE=DATE-TIME:20210106T133000Z
DTEND;VALUE=DATE-TIME:20210106T150000Z
DTSTAMP;VALUE=DATE-TIME:20201129T215200Z
UID:indico-event-360@indico.knu.ac.kr
DESCRIPTION:Speakers: John C. Collins (Penn State U.)\nIt is often stated
that the vacuum is trivial when light-front is used\, in contrast to equal
-time quantization. In fact this is not the case\, as has been known sin
ce 1969. I give an elementary review of why this happens\, and locate an e
asy-to-miss but elementary mathematical error in proofs of vacuum triviali
ty.\n\nIn the light of this\, a careful re-examination and reformulation o
f the mathematics of light-front quantization is needed\, and I lay out a
program to do this. The program builds on some already-known mathematica
l complications that are easily overlooked.\n\n(Some of the material in th
is seminar is in arXiv:1801.03960.)\n\nWebinar at https://meet.jit.si/ILCA
Cseminar\nhttps://indico.knu.ac.kr/event/360/
LOCATION:
URL:https://indico.knu.ac.kr/event/360/
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SUMMARY:Proton mass decompositions
DTSTART;VALUE=DATE-TIME:20210120T133000Z
DTEND;VALUE=DATE-TIME:20210120T150000Z
DTSTAMP;VALUE=DATE-TIME:20201129T215200Z
UID:indico-event-442@indico.knu.ac.kr
DESCRIPTION:Speakers: Andreas Metz (Temple U.)\nDifferent decompositions (
sum rules) for the proton mass have been proposed in the literature. All o
f them are related to the energy-momentum tensor in quantum chromodynamics
. In this talk\, I report on recent work where we review and revisit these
decompositions by paying special attention to recent developments with re
gard to the renormalization of the energy-momentum tensor. The connection
between the sum rules is discussed as well. I present numerical results fo
r the various terms of the mass decompositions up to 3 loops in the strong
coupling\, and consider their scheme dependence. The role played by the t
race anomaly and the sigma terms will be discussed as well. I will also di
scuss how\, according to the current state of research\, a future electron
-ion collider might be able to contribute to the understanding of the prot
on mass decomposition.\nhttps://indico.knu.ac.kr/event/442/
LOCATION:
URL:https://indico.knu.ac.kr/event/442/
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BEGIN:VEVENT
SUMMARY:TBA
DTSTART;VALUE=DATE-TIME:20210203T133000Z
DTEND;VALUE=DATE-TIME:20210203T150000Z
DTSTAMP;VALUE=DATE-TIME:20201129T215200Z
UID:indico-event-441@indico.knu.ac.kr
DESCRIPTION:Speakers: Shohini Bhattacharya (Temple U.)\nhttps://indico.knu
.ac.kr/event/441/
LOCATION:
URL:https://indico.knu.ac.kr/event/441/
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