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SUMMARY:Tunneling in QFT 2024
DTSTART:20240111T130000Z
DTEND:20241212T130000Z
DTSTAMP:20240622T043600Z
UID:indico-event-1346195@indico.cern.ch
CONTACT:andreas.ekstedt@physics.uu.se\;oliver.gould@nottingham.ac.uk\;miha
.nemevsek@ijs.si
DESCRIPTION:Seminar series devoted to tunneling in QFT\nMonthly on Thursda
ys\, usually @ 14:00 for Central Europe (CEST in European summer and CET i
n winter)\nWhether it be vacuum stability\, phase transitions\, or analogu
e quantum systems\, tunneling is part and parcel of quantum field theory.
In this seminar series we explore new developments in our understanding of
these phenomena.\n\nPlease register on this Indico page to receive Zoom j
oining instructions plus a reminder for each talk.\nUpcoming seminars
\n\nLaura Batini (University of Heidelberg): 11 July at 14:00 CEST (07:00
Chicago\, 20:00 Shanghai)Tunneling in string breaking and implications for
hadronizationWe study the pair production\, string breaking\, and hadroni
zation of a receding electron-positron pair using the bosonized version of
the massive Schwinger model in quantum electrodynamics in 1+1 space-time
dimensions. Specifically\, we study the dynamics of the electric field in
Bjorken coordinates by splitting it into a coherent field and its Gaussian
fluctuations. We find that the electric field shows damped oscillations\,
reflecting pair production. Interestingly\, the computation of the asympt
otic total particle density per rapidity interval for large masses can be
fitted using a Boltzmann factor\, where the temperature can be related to
the hadronizationtemperature in QCD. Lastly\, we discuss the possibility o
f an analog quantum simulation of the massive Schwinger model using ultrac
old atoms\, explicitly matching the potential of the Schwinger model to th
e effective potential for the relative phase of two linearly coupled Bose-
Einstein condensates.\n\nPrevious seminars\n(Previous talks are uploaded a
t www.youtube.com/@TunnelingQFT )\n\nWen-yuan Ai (King's College London):
13 June 2024Self-consistent bounces in bubble nucleationStudies on false v
acuum decay are usually based on Callan and Coleman's semi-classical formu
la. This formula does not tell us how to compute quantum corrections to th
e classical bounce\, i.e.\, classical critical bubble. Even worse\, there
are situations in which bounce solutions do not exist at the classical lev
el but only emerge from radiative corrections. In this talk\, I will show
how the n-particle-irreducible (nPI) effective action formalism can perfec
tly deal with these problems. Although I will mostly focus on how to compu
te quantum corrections to the bounce at zero temperature using the 1PI eff
ective action\, I will also briefly discuss how to study the backreactions
from the bounce to the plasma at finite temperature using the 2PI effecti
ve action.\nLorenzo Ubaldi (Jožef Stefan Institute and Ljubljana Universi
ty): 16 May 2024False vacuum decay from thin to thick wallsThe computation
of the false vacuum decay rate in the situation with nearly degenerate va
cua can be performed analytically in the well known thin wall approximatio
n. If we depart from the near degeneracy of the vacua\, the approximation
quickly ceases to work. This statement is known to practitioners of the fi
eld\, but it has a caveat: it is true only if one works at the leading ord
er of the thin wall approximation. In this talk I will describe how to org
anize the calculation to systematically include higher order corrections i
n the thin wall parameter expansion. The first few orders can be computed
analytically. It is enough to include them to improve the approximation an
d get a very accurate estimate of the bounce action also deep into thick w
all regimes\, where the vacua are far apart. I plan to also briefly discus
s how to deal in these cases with the calculation of the functional determ
inant\, also known as the prefactor\, in order to have the full proper und
erstanding of the vacuum decay rate. In the whole talk I will only conside
r flat spacetime\, without gravity.\nPatrick Draper (Illinois University\
, Urbana): 18 April 2024Tunneling with Time DependenceI will discuss semic
lassical methods for studying bubble nucleation in models with parameters
that vary slowly in time. Introducing a more general rotation of the time
contour allows access to a larger set of final states\, and typically a no
n-Euclidean rotation is necessary in order to find the most relevant tunne
ling solution. The method is straightforward to implement for thin wall bu
bble nucleation. I also describe some examples where gravitational effects
are included\, and give one example of an exact instanton solution in a t
ime-dependent Kaluza-Klein cosmology.\nYutaro Shoji (Jožef Stefan Institu
te and Ljubljana University): 14 March 2024Gauge invariance and gauge zero
modes of bubble nucleation ratesA precise computation of a vacuum decay r
ate requires the determination of the prefactor in front of the exponentia
l suppression factor. When the decay is driven by charged scalar field(s)\
, the prefactor includes the functional determinants of the gauge boson an
d the Faddeev-Popov fluctuation operators. They depend on the gauge fixing
parameter non-trivially and it has not been clear how this dependence can
cels out in the final results. We have explicitly proven that the function
al determinants become independent of the gauge parameter for a general se
tup with multiple scalar and gauge fields. The subtraction of the gauge z
ero modes is necessary to make the functional determinant finite. The path
integral over these zero modes is translated into an integration over the
collective coordinates\, requiring a Jacobian. Due to the gauge fixing te
rms\, the Jacobian becomes non-trivial and gauge-dependent. We have determ
ined the correct Jacobian\, which makes it possible to calculate the prefa
ctor for general scalar and gauge fields.\nSilvia Pla Garcia (Kings Colle
ge\, London): 8 February 2024Can quantum tunnelling induce a cosmic bounce
?If we imagine rewinding the universe to early times\, the scale factor sh
rinks and the existence of a finite spatial volume may play a role in quan
tum tunnelling effects in a closed universe. In this talk\, I will present
a novel mechanism to induce a cosmological bounce that is purely generate
d by quantum fluctuations without the need for exotic matter or modified g
ravity. The quantum-induced bounce emerges when we allow a scalar field to
tunnel between two degenerate minima. I will also explain how the picture
can change in the presence of anisotropies\, identifying a criterium for
a successful bounce in terms of the size of the closed universe and the pr
operties of the quantum field.\nIan Moss (Newcastle University): 11 Janua
ry 2024The hot big bang in a cold gasFalse vacuum decay is a fascinating t
heoretical prediction of non-perturbative quantum field theory\, and one t
hat has many implications for the early universe\, ranging from the format
ion of matter to the origin of the universe as a quantum event. I’ll exp
lain some of the basic ideas\, and discuss the first observations of therm
al vacuum decay in an atomic condensate.\n\nOrganisers\n\nAndreas Ekstedt
(Uppsala University)\nOliver Gould (University of Nottingham)\nMiha Nemev
šek (Jožef Stefan Institute and University of Ljubljana)\n\n\nhttps://in
dico.cern.ch/event/1346195/
URL:https://indico.cern.ch/event/1346195/
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