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SUMMARY:Orthogonality catastrophe in perturbed CFTs - Anatoly Konechny (He
 riot-Watt University)
DTSTART:20250916T130000Z
DTEND:20250916T140000Z
UID:TALK235639@talks.cam.ac.uk
DESCRIPTION:We consider d-dimensional Euclidean CFTs on a cylinder perturb
 ed by a relevant or marginal operator. We discuss perturbation theory seri
 es for the components of the perturbed theory vacuum and show that they ha
 ve a new kind of divergences&nbsp\; that appear when the dimension of the 
 perturbing operator exceeds the threshold value of (d+1)/2. If left unreno
 rmalised these divergences make&nbsp\; the overlap of the perturbed and un
 perturbed theory vacua vanish that is known in the literature as the ortho
 gonality catastrophe. We discuss renormalisation of the vacuum vector in t
 erms of the interface between the perturbed and unperturbed theories and p
 ossible implications for truncated Hamiltonian techniques. A number of exp
 licit examples will be&nbsp\; discussed as well as some old results&nbsp\;
  which are usually linked to Haag&rsquo\;s theorem in infinite volume.
LOCATION:Seminar Room 2\, Newton Institute
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