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SUMMARY:The Dark Side of the Propagators: analytical approach to QCD in t
he infrared of Minkowski space.
DTSTART;VALUE=DATE-TIME:20160729T163000Z
DTEND;VALUE=DATE-TIME:20160729T165000Z
DTSTAMP;VALUE=DATE-TIME:20191018T140747Z
UID:indico-contribution-2437@conference.ippp.dur.ac.uk
DESCRIPTION:Speakers: Fabio SIRINGO (Dipartimento di Fisica e Astronomia\,
Università di Catania)\nSince most of the non-perturbative approaches to
QCD rely on numerical calculations in the *Euclidean* space\, many import
ant dynamical information cannot be easily extracted because of the ill-de
fined problem of analytic continuation for a limited set of data points.\n
On the other hand\, by a shift of the expansion point\, a perturbative app
roach has been developed[1\,2] that has the nice feature of providing one-
loop analytical functions for the propagators that are in perfect agreemen
t with the data of lattice simulations in the Euclidean space. These funct
ions are generally analytic and can be studied in Minkowski space\, yieldi
ng a direct proof of positivity violation and confinement.\n\nThe expansio
n has been extended to full QCD [3]\, including a set of chiral quarks\, i
n order to give a unified description of dynamical mass generation and chi
ral symmetry breaking\, yielding new insights on the coupled quark\, gluon
and ghost propagators in the infrared of Minkowski space\, that is still
basically unexplored.\n\nWhile dealing with the exact Lagrangian\, the mod
ified expansion is based on *massive* free-particle propagators\, is safe
in the infrared and is equivalent to the standard perturbation theory in t
he UV [2\,3]. By dimensional regularization\, all diverging mass terms can
cel exactly without including spurious mass counterterms that would spoil
the gauge and chiral symmetry of the Lagrangian. If optimized\, the *mass
ive* expansion provides a variational tool disguised to look like a pertur
bative method\, without any phenomenological parameter\, from first princi
ples.\n\nAmong the main findings\, universal scaling properties are predic
ted for the inverse dressing functions and shown to be satisfied by the la
ttice data. Complex conjugated poles are found for the gluon propagator\,
in agreement with the *i-particle* scenario. No complex poles are found fo
r the quark propagators but the positivity constraints of the spectral fun
ctions are badly violated by the explicit presence of\nnegative-norm multi
particle states below the two-particle threshold.\n\n\n----------\n\n\n [1
] F. Siringo\, *Perturbative study of Yang-Mills theory in the infrared*\,
arXiv:1509.05891.\n\n [2] F. Siringo\, *Analytical study of Yang-Mills t
heory in the infrared from first principles*\, Nucl.Phys.B907\, 572 (2016)
\; arXiv:1511.01015.\n\n [3] F. Siringo\, *Analytic structure of QCD propa
gators in Minkowski space*\, arXiv:1605.07357\n\nhttps://conference.ippp.d
ur.ac.uk/event/470/contributions/2437/
LOCATION:Highfield Campus\, University of Southampton Building 67 Room 100
7
URL:https://conference.ippp.dur.ac.uk/event/470/contributions/2437/
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