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SUMMARY:Living with the ghosts
DTSTART:20150223T140000
DTSTAMP:20260406T172827Z
UID:8bce14765239e6cf4638dfce91fb805d595a254e84c86c6192029caf
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr Andrey Smilga (Universite of Nantes)\nLagrangians with hig
 her derivatives  involve  "ghosts" meaning that their Hamiltonian is not
  bounded neither from below\, nor from above. Most people think that it is
  a disaster and ruins the theory completely.\nMy point\, however\, is that
  it is not so. There is no problem whatsoever in free theory. Consider e.g
 . the Hamiltonian representing a difference of two usual harmonic oscillat
 or Hamiltonians. The spectrum  $E_{nm} = \\omega_1(n+1/2) - \\omega_2(m+ 
 1/2)$  does not have a bottom\, but the Hilbert space is well defined  a
 nd the evolution operator is unitary.\n  Typically\, ghosts strike back w
 hen one includes interaction. One observes a collapse (the phenomenon of t
 he same nature as falling on the center in the attractive $1/r^2$  potent
 ial) and violation of unitarity. But there are some special nontrivial int
 eractive systems when the ghosts are "benign" and collapse does not occur.
  There are several QM examples and one interesting  2d field theory examp
 le.\n  It  is not  thus  forbidden now to dream  that a real fundamen
 tal Theory of Everything represents a higher-derivative theory living in a
  flat higher-dimensional  bulk and our World lives on its 3-brane classic
 al solution.
LOCATION:Cubotron 727
STATUS:CONFIRMED
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