# DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS

## HIP seminar room A315

**Tuesday 22 May 2018 at 14.15 in A315: Javier Tarrio (Brussels) Note special time!**

*Holography, cold dense matter and color superconductivity*

Abstract: I will describe a model of a strongly interacting plasma with fundamental matter at finite density that arises in string theory. In a recent work the simplest phase of this system was studied, and instabilities towards more complicated phases were found. I will discuss in some more detail the instability towards the breaking of the gauge group, which gives rise to color superconductivity.**Special seminar: Wednesday 23 May 2018 at 15 at Aalto university: Frank Wilczek (MIT, Stockholm)**

*Emergent Axions, and the Challenging Search for Real Ones*

Abstract: The effective theory of axion electrodynamics governs interesting transport phenomena in real materials (topological insulators). I’ll discuss how the theory emerges from very basic considerations, and also review some confirming experiments. Then I’ll discuss recent proposals for experiments to detect the cosmic axion background, which push interesting frontiers of detector technology.**Special colloquium: Thursday 24 May 2018 at 17 at Helsinki university, Great hall (juhlasali): Frank Wilczek (MIT, Stockholm)**

*The Strange, Unfinished Story of Time Reversal*

Abstract: Few aspects of experience are as striking as the difference between past and future. Yet the fundamental equations of physics make no such distinction. Why is that? And how can the world look so different from the equations? Physicists have wrestled with those questions for centuries, yet they remain alive as frontiers of research.**Tuesday 5 June 2018 at 10.15 in A315: Kirill Boguslavski (Jyväskylä)**

*Spectral function from real-time lattice gauge simulations*

Abstract: We study the spectral properties of a highly occupied non-Abelian non-equilibrium plasma appearing ubiquitously in weak coupling descriptions of QCD matter. The spectral function of this far-from-equilibrium plasma is measured by employing linear response theory in classical-statistical real-time lattice Yang-Mills simulations. We establish the existence of transversely and longitudinally polarized quasiparticles and obtain their dispersion relations, effective mass, plasmon frequency, damping rate and further structures in the spectral and statistical functions. Our results are consistent with hard thermal loop (HTL) effective theory but also indicate effects surpassing its leading order. The method can be employed beyond the range of validity of HTL.**Tuesday 12 June 2018 at 10.15 in A315: Kai Nordlund (Helsinki)**

*Using molecular dynamics to aid dark matter searches*

Abstract: There are a number of attempts for direct detection of dark matter particles via their elastic interaction with detector nuclei. To date, the detectors developed could detect dark matter particles with masses > 10 GeV/c^2. In this work [1], we showed that potential dark matter particles in the mass range down to 200 MeV/c^2 could be detected by new kinds of single-electron resolution single crystal semiconductor detectors. The dark matter particles in this mass range, if they exist, could give the detector nuclei recoils in the energy range 1 — 100 eV. If this is the case, the detector response can be calibrated with molecular dynamics simulations of low-energy self-recoils in the material. We used classical and time-dependent density functional theory molecular dynamics to calculate the response of the semiconductor detectors to dark matter recoils as a function of crystal direction, and using an analytical model translated this into a dependence of the signal on the time of the day. The diurnal variation could be a major benefit for distinguishing a dark matter particle signal from that of conventional standard model particles.

[1] F. Kadribasic, N. Mirabolfathi, K. Nordlund, A. E. Sand, E. Holmström, and F. Djurabekova, Directional Sensitivity In Light-Mass Dark Matter Searches With Single-Electron Resolution Ionization Detectors, Phys. Rev. Lett 120, 111301 (2018)**Tuesday 7 August 2018 at 10.15 in A315: Mikko Laine (Bern)**

*TBA*

Abstract: TBA**Tuesday 11 November 2018 at 10.15 in A315: Michael Ramsey-Musolf (UMass Amherst)**

*TBA*

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) [department / HIP seminar],

Francesco Montanari (francesco montanari at helsinki fi) [cosmo seminar]

**Other related seminars**

Friday 10-12 seminar series in D117: Astrophysics seminar.

Mathematical Physics Seminar and Workshop series Wed 14-16 in Exactum C123.