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SUMMARY:Theory seminar: Anna Tokareva (HIAS)
DTSTART:20240208T150000Z
DTEND:20240208T160000Z
DTSTAMP:20240425T100300Z
UID:indico-event-5215@indico.nikhef.nl
DESCRIPTION:Very basic assumptions about the structure of the fundamental
theory describing the nature at high energies can allow for a set of valua
ble constraints on the low energy EFT. This approach provides constraints
that are independent of the concrete underlying fundamental theory at high
energies. The low energy physics is bounded from the set of quite natural
assumptions about the structure of the full theory\, such as unitarity\,
causality and Lorentz invariance. In this talk I will consider the EFT of
photons (or other U(1) gauge field) and compare different approaches to ob
tain bounds on its Wilson coefficients. I will present an analytic derivat
ion of the implications of unitarity (linear and non-linear positivity bou
nds) and compare these constraints with the requirement of causal propagat
ion of the photon modes around non-trivial backgrounds generated by extern
al sources. I will show that the low energy causality condition can give c
omplementary constraints to the positivity bounds. Applying both constrain
ts together can significantly reduce the allowed region of the photon EFT
parameters. Besides constraints on the IR theory\, the analyticity and uni
tarity assumptions can set bounds on the UV theory. I will show this conne
ction using the example of the graviton mediated scattering amplitudes. Su
rprisingly\, the form of the forward limit singularities at low energies c
an give an insight into the of high energy limit of graviton scattering de
scribed by the unknown physics.\n\nhttps://indico.nikhef.nl/event/5215/
URL:https://indico.nikhef.nl/event/5215/
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