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SUMMARY:pNGBs under finite temperature
DTSTART;VALUE=DATE-TIME:20230915T131500Z
DTEND;VALUE=DATE-TIME:20230915T133000Z
DTSTAMP;VALUE=DATE-TIME:20260405T225748Z
UID:indico-contribution-37@cern.ch
DESCRIPTION:Speakers: Dr. KOUTROULIS\, Fotis (Warsaw University)\nThe true
  nature of the Higgs particle (is it fundamental or composite?) is still u
 nder investigation.\nOne plausible realization\, which provides also a sol
 ution to the ElectroWeak hierarchy problem\, is to identify the Higgs fiel
 d with one of the pseudo-Nambu-Goldstone bosons (pNGBs) arising from the s
 pontaneous and explicit breaking of a global symmetry at some UV scale. Ho
 wever\, for the physically relevant scenarios this Effective Field Theory 
 (EFT) description demands a non-negligible fine-tuning in order to explain
  the scale-separation and in most of the times the associated effective po
 tential becomes a source of EFT’s break down so the latter cannot be tru
 sted.\nIn this work we give an example where both the previous concerns ar
 e resolved.\nIn particular\, we consider an EFT containing the pNGBs arisi
 ng from the breaking of an approximate global symmetry at the scale f wher
 e in all of our applications we will be interested in the scenarios in whi
 ch the spontaneous and explicit symmetry breaking is of the SO(N+1) --> SO
 (N) pattern. The produced pNGBs span a space of non-trivial geometry which
  consists of the set of points a fixed distance from the origin in R^{N+1}
 .\nUnder this framework we evaluate the effective potential at 1-loop orde
 r including both the zero- and finite-temperature corrections and analyze 
 the thermal history of the model. Key characteristic of our case is the de
 mand of a radiatively and thermally stable effective potential. This natur
 ally leads us to consider the Laplace-Beltram eigenvalue as our tree level
 \, zero-temperature\, potential which corresponds to the well-known Gegenb
 auer polynomials. The latter offer multiple non-degenerate vacua that can 
 generate a natural hierarchy of scales between the pseudo-Golstone masses 
 and the scale of spontaneous symmetry breaking\, provided the order of the
  polynomial is large enough. \nMoreover choosing the Gegenbauer polynomial
 s we are in position to determine\, obtaining an upper bound for only one 
 single parameter\, when quantum and thermal corrections are free of incons
 istencies keeping the effective potential real and rendering the EFT descr
 iption valid. Since the latter is ensured we find that the model exhibits 
 a weak first order phase transition via thermal fluctuations which lead to
  the production of Gravitational Wave (GW) signals which however are very 
 weak.\nOn the other hand\, as a final step of our analysis we assume that 
 the above pNGB model corresponds to a hidden sector which is not themalize
 d during reheating. As a consequence\, the model exhibits a first order ph
 ase transition merely via tunnelling which means that the transition is st
 rong and we show that there is a parameter space for which the associated 
 GW signals are stronger and could be detected by the current and future ex
 periments.\n\nhttp://indico.fuw.edu.pl/contributionDisplay.py?contribId=37
 &sessionId=16&confId=66
LOCATION:University of Warsaw\, Faculty of Physics 0.03a
URL:http://indico.fuw.edu.pl/contributionDisplay.py?contribId=37&sessionId
 =16&confId=66
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