## DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2023

Angle-resolved photoemission spectroscopy (ARPES) measurements in the pseudogap phase of cuprates reveal a Fermi surface seemingly made up of disconnected arcs: the electron spectral function exhibits sharp peaks in certain directions in momentum space, which appear to blur into a continuum in other directions. This phenomenon is known as nodal-antinodal dichotomy. I will discuss how this dichotomy can be realised in holography through an anisotropic infrared scaling symmetry. I will begin with a general analysis of the low-frequency behaviour of fermion spectral functions in holographic systems with such scaling. I will then show our calculations of the spectral function in an example model, providing a clear demonstration of the scaling-based mechanism for realising the dichotomy.**Tuesday 4 April 2023 at 10:15 in A315 and using Zoom: Ronnie Rodgers (Nordita)**Holographic nodal-antinodal dichotomy from infrared scaling

Abstract:Fundamental dimensionless constants like the fine-structure constant and electron-to-proton mass ratio can vary as a function of time if an ultralight scalar field couples to the standard model. Detecting such variations may be possible by utilising the exceptional sensitivity of atomic clocks, some of which now operate with relative uncertainties of parts in one quintillion. Using data on strontium, ytterbium and caesium clock transitions collected by the National Physical Laboratory in the UK, fine-structure constant and electron-to-proton mass ratio variations have been probed on timescales ranging from a minute to almost a day. These results enable the extraction of model-independent constraints on low-dimensional scalar-QED and scalar-QCD couplings and models of ultralight scalar and axion-like dark matter.**Tuesday 2 May 2023 at 10:15 in A315 and using Zoom: Nathan Sherrill (Sussex)**Probing ultralight scalar fields with atomic clocks

Abstract:TBA**Tuesday 23 May 2023 at 10:15 in A315 and using Zoom: Viljami Leino (Mainz)**TBA

Abstract:Quantum coherence plays essential role in diverse phenomena in the early universe. Examples include activation of sterile neutrinos, electroweak baryogenesis, resonant leptogenesis and particle production in phase transitions and during the (p)reheating stage after inflation. Each of the above corresponds to an out-of-equilibrium system with some essential quantum information evolving in the presence of decohering collisions. Historically such problems have been addressed with a wide range of specifically tailored methods and approximations. I will show that at the fundamental level all such problems can be addressed by a unified theoretical framework, from which suitable quantum transport equations can be derived in the appropriate limits. In particular, I will highlight some recent results in the electroweak baryogenesis and in the resonant leptogenesis.**Tuesday 30 May 2023 at 10:15 in A315 and using Zoom: Kimmo Kainulainen (Jyväskylä)**The quantum early universe

Abstract:**Thursday 29 June 2023 at 10:15 in A315 and using Zoom: Christophe Royon (University of Kansas)**TBA

Abstract:TBA**Tuesday 5 December 2023 at 10:15 in A315 and using Zoom: Riina Virta (STUK, Radiation and Nuclear Safety Authority, HIP)**Verifying spent nuclear fuel with Passive Gamma Emission Tomography (PGET)

Abstract: TBA

*Hopefully the up to 50 min + 10 min discussion long seminar/colloquium will be understandable to a wide audience.
Contacts: Keijo Kajantie (keijo kajantie at helsinki fi) [ HIP seminar],
Jaakko Annala (jaakko annala at helsinki fi) [cosmo seminar]*

New Nordic series of seminars over the web, link: https://sites.google.com/view/nordictheory/home

For more information, and to subscribe to email announcements, contact Oscar Henriksson (oscar henriksson at helsinki fi)

**Other related seminars**

*Friday 10-12 seminar series in A315:Astrophysics seminar.
Mathematical Physics Seminar and Workshop series Wed 14-16 in Exactum C123.*

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