DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2023

• Tuesday 10 January 2023 at 10:15  in A315 and using Zoom: Tuomas Lappi (Jyväskylä)
  EIC – the most powerful microscope on Earth
  Abstract: This seminar will discuss the physics program of the Electron-Ion Collider EIC. The EIC is a collider for DIS, deep inelastic scattering, that should start taking data in the early 2030’s. It will be built at Brookhaven, combining the existing proton and ion beams of RHIC with a new electron accelerator. The EIC will be the first collider energy DIS experiment with polarized protons, and the first to collide heavy ions. It will also have a luminosity orders of magnitude higher than previous HERA experiments. These features allow the EIC to access new aspects of gluonic degrees of freedom in ordinary matter. The nuclear beam will enable precision studies of gluon saturation in a high energy nucleus. Polarization gives access to the role of gluons in the proton spin, moving us closer to understanding the proton spin puzzle. The high luminosity enables measurements of rare exclusive processes that lead to a multidimensional mapping of the structure of the proton.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=938267a6-b919-4d0b-bed5-cd806b9391e7
• Tuesday 24 January 2023 at 10:15  using Zoom: Sophia Han (T.D.Lee Institute, Shanghai)
  Probing exotic matter in neutron star cores with g-mode oscillations
  Abstract: The neutron star interior reaches ultra-high densities with its composition details unknown. Gravitational wave emissions from neutron stars are promising probes that can help reveal novel phases of dense matter. In this talk, I will describe a first study of the principle g-mode oscillation in hybrid stars containing quark matter through hadron-quark crossover transition, and compare with results obtained for a first-order transition via the Gibbs mixed-phase construction. I will discuss the distinct behaviors of the adiabatic and equilibrium sound speeds in theoretical models of the equation of state (EoS) for neutron-star matter, as well as their connections to astrophysical observables.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=9cb72fe9-c5bc-4db1-9daa-0a4edb91319d
• Tuesday 31 January 2023 at 10:15 in A315 and using Zoom: Niklas Ramberg (Mainz)
  Bubbles from Dark Confinement with Holography
  Abstract:Gravitational waves emitted from strongly coupled QFTs are, at present, a daunting task to accurately predict due to the strong coupling. In this talk, we demonstrate how to predict the gravitational wave spectra of such theories using holography and lattice data input for a pure SU(3) Yang-Mills theory with minor uncertainties. We will elaborate on how we obtain an effective potential using holography with the free energy landscape approach and formulate an effective action. Once the effective action is in our grasp, we will use this to study bubble nucleation to predict the gravitational wave spectra.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=bc5974b8-5bb2-4bde-9070-c238ad0e3571
• Tuesday 7 February 2023 at 10:15 in A315 and using Zoom: Andrea Malara (Brussels U, IIHE)
  Reconstruction and calibration of jets at the CMS experiment: Run 2 and perspective for Run 3
  Abstract: Abundantly produced at hadron colliders and appearing as a cluster of energy, jets are the experimental signature of strongly interacting particles. A detailed understanding of jet properties and precise jet calibration are essential for the success of the LHC physics program and becomes increasingly more crucial as more data is collected.  The imminent Run 3 at the LHC paves the way to an era of unprecedented precision.  The knowledge acquired during the previous data-taking periods, both in understanding the detector and in the evolution of analysis strategies, will allow for a calibration accuracy below the per mille level. As a consequence, all CMS physics analyses will profit from the substantial reduction of uncertainties.
  I will discuss the latest and greatest techniques adopted in CMS for jet calibration, elaborate on the impact on physics analysis and highlight future perspectives in this field.
  
• Tuesday 21 February 2023 at 10:15 in A315 and using Zoom: Harri Waltari (Uppsala)
  The anatomy of Higgs pair production with light stops
  Abstract: The discovery of Higgs pair production is one of the main targets the coming runs of the LHC. In the SM the gluon-initiated process has a destructive interference between the triangle and the box diagrams, which makes Higgs pair production a potential probe of BSM physics. We performed an amplitude-level analysis of Higgs pair production at the LHC in the presence of light stops. We show what types of deviations one could expect and how they arise from different new physics contributions. The toolbox can be used also to different scenarios with additional colored scalars coupling to the Higgs.
• Tuesday 4 April 2023 at 10:15 in A315 and using Zoom: Ronnie Rodgers (Nordita)
  Holographic nodal-antinodal dichotomy from infrared scaling
  Abstract: 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.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=e970464a-4572-4c18-8831-99776861f1dc
• Tuesday 25 April 2023 at 10:15 in A315 and using Zoom: Saga Säppi (Munich)
  Updates on finite-density perturbative QCD: pressure with soft gluons, complex analysis and loops, and quark masses
  Abstract: As the often-repeated tagline goes, understanding the behaviour of matter at finite density has become increasingly important in recent years: Shifting perturbative QCD to finite chemical potential allows us to shed light to the behaviour of neutron stars (and specifically their dense cores). LIGO and its friends are measuring gravitational waves from neutron star collisions, and improved telescopes give more and more precise measurements of the properties of quiescent neutron stars. I will focus on the theory side of things, starting with a general overview of how the calculations work—and hopefully why I find them fun and interesting!—and follow with more detailed discussion of recent works: Starting with the pressure, and an update on calculations pushing it closer and closer to next-to-next-to-next-to-leading order accuracy using hard thermal loops, following with an interesting observation about computing zero-temperature and finite-density loop integrals, and finishing by showing off an efficient way of accounting for finite-quark-mass effects and an application to computing the bulk viscosity.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=9b77b77e-420b-4152-bc44-3cc8925ba07f
• Tuesday 2 May 2023 at 10:15 in A315 and using Zoom: Nathan Sherrill (Sussex)
  Probing ultralight scalar fields with atomic clocks
  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.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=89283099-8572-4992-a120-4de884abeea8
• Tuesday 9 May 2023 at 10:15 in A315 and using Zoom: Marco Ornigotti (Tampere)
  Gauge Fields, Topology, and the Optical Response of 2D Materials
  Abstract: In this talk, I will give an introduction to 2D materials and how to calculate their nonlinear optical response, in terms of spectrum of emitted harmonics. After this, I will focus on showing what are the effects of (artificial) gauge fields and topological transitions on such a response, and how one could use the nonlinear optical response as a probe for topological transitions occurring in 2D and, to some extent, 3D materials. Graphene will be mainly used as a platform to test this ideas and understand these results, but I will also show some results in other 2D materials, such as Weyl semimetals.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=dab046bb-d1d8-4dd1-845c-316d2a9233e6
• Wednesday 10 May 2023 at 10:15 in A315 and using Zoom: Christer Fröjdh (Mittuniversitetet, Sundsvall)
  Spectral X-ray detection and imaging
  Abstract: For several decades film was the dominating sensor for X-ray imaging. The contrast in such an image is a function of the energy deposited in each point in the film. However, if the energy of each photon could be registered significantly more information can be obtained using the same amount of radiation. Recent developments in microelectronics have opened up for the development of detectors with single photon processing where both the energy and the time of arrival of each photon can be registered.  This seminar will cover some fundamentals of radiation interaction with matter, recent development in spectroscopic radiation detectors, fundamentals of spectral imaging and some challenges for the future.
• Tuesday 16 May 2023 at 10:15 in A315 and using Zoom: Juuso Österman (Helsinki)
  Feynman integrals at finite density and vanishing temperature: complex analysis and Integration-by-Parts relations
  Abstract: In the context of studying the thermodynamic properties of extremely dense systems such as  neutron-star cores, perturbative QCD has been pushed to involve particularly high order loop corrections. These corrections can be discussed in terms of Feynman integrals in Euclidean finite temperature field theory and contain notably an imaginary scale, the chemical potential. In this talk, I will address non-trivial properties of such Feynman integrals in the limit of vanishing temperature occurring already at the one-loop level. In the complex contour formalism, the role of a small but non-vanishing temperature as a regulator is pronounced. The temperature regulation can be applied to two interesting evaluation methods: the theorem of residues and Integration-by-Parts (IBP) relations. Their augmentations, arising from infinitesimal temperature, are seen as sums of lower-dimensional complex-valued loop integrals. These augmentations pave the way for a full d+1-dimensional IBP description of Feynman integrals equipped with an imaginary scale at the vanishing-temperature limit.
• Tuesday 23 May 2023 at 10:15 in A315 and using Zoom: Viljami Leino (Mainz)
  Heavy quark momentum diffusion from lattice simulations
  Abstract: The matter produced in heavy ion collisions can be characterized as a  strongly coupled quark gluon plasma. Within this plasma, the heavy  quarks can be seen to behave with Langevin dynamics, with the diffusion  expressed with heavy quark momentum diffusion coefficient. The heavy  quark diffusion coefficient is encoded in the spectral functions of the  Euclidean chromo-electric and the chromo-magnetic correlators that are calculable on the lattice. We study the chromo-electric and the
  chromo-magnetic correlator in the deconfined phase of SU(3) gauge theory using lattice field theory simulations. We present the results in a very wide temperature range allowing us to connect to perturbation theory and observe the temperature dependence of this quantity.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=33e8c06f-acc6-489d-b20d-7513bc0a2778
• Tuesday 30 May 2023 at 10:15 in A315 and using Zoom: Kimmo Kainulainen (Jyväskylä)
  The quantum early universe
  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.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=5c79d273-3527-4845-a890-8f50f9630975
• Tuesday 30 May 2023 at 16.15 using Zoom: Paul Romatschke (Boulder) Note time!
  What if phi^4 theory in 4 dimensions is non-trivial in the continuum?
  Abstract: Traditionally, scalar phi^4 theory in four dimensions is thought to be quantum trivial in the continuum. In this talk, I critically review what quantum triviality is, and in particular which parts of the idea have actually been mathematically proved as opposed to just assumed to be true. I go on to exploit loopholes in the mathematical proofs, notably multi-component fields, to present aconcrete calculation that avoids quantum triviality in  scalar phi4 theory in the continuum. There is a price to pay to avoid triviality, but there are also potentially rich rewards. Your mileage will vary. Whatever the outcome, it is great fun to work on this subject!
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=4ec521cb-86da-439e-8b43-c7001b588fe7
• Tuesday 6 June 2023 at 10:15 in A315 and using Zoom: Daniel Litim (Sussex)
  Interacting UV fixed points – from quantum field theory to quantum gravity
  Abstract: It is a fascinating idea that all the physics as we know it could arise as a small perturbation of some UV conformal field theory. This necessitates that the running couplings of the underlying quantum field theory achieve a fixed point in the UV, such as in asymptotic freedom. In this talk, I discuss the prospects for QFTs to develop interacting UV fixed points, covering weakly and strongly coupled 4d QFTs, perturbatively  non-renormalisable theories such as 3d fermionic QFTs, and 4d quantum gravity. I will give an overview of rigorous results and methodologies, and address open challenges for quantum gravity.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=5af66ebe-3a44-4ec3-82fb-ff36f15fd9c5
• Tuesday 13 June 2023 at 10:15 in A315 and using Zoom: Otto Hannuksela (Hong Kong)
  Gravitational-wave astronomy
  Abstract: We have entered the era of gravitational-wave astronomy. With nearly 100 published gravitational-wave detections, the LIGO-Virgo-Kagra collaboration is preparing for the next observing run with upgraded detector sensitivities. In parallel, third-generation detectors such as the Einstein Telescope and Cosmic Explorer and space-based detectors such as LISA are being planned. In the future, the field of gravitational waves is expected to be revolutionized many times over. Here I will discuss our recent work in the field and outline select future directions.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=07e4ce07-f09d-4095-a43b-70a11b559875
• Thursday 29 June 2023 at 10:15 in A315 and using Zoom: Christophe Royon (University of Kansas)
  Measuring intact protons at the LHC: From the odderon discovery to the search for axion-like particles
  Abstract: In the first part of the talk, we will describe the odderon discovery by the TOTEM and D0 experiments. The analysis compares the p-pbar elastic cross section as measured by the D0  Collaboration at Fermilab at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at CERN at 2.76, 7, 8, and 13 TeV. The two data sets disagree at the 3.4 sigma level and thus provide evidence for the odderon. Combining these results with previous TOTEM results leads to a combined significance larger than 5 sigma.
  In a second part of the talk, we will describe the search for axion-like particles with intact protons in the final state, leading to sensitivities to beyond standard model physics that improve by 2 to 3 orders of magnitude on the coupling compared to LHC standard methods.
  We will finish by describing briefly the ultra fast silicon detectors for timing measurements as well as for medical and cosmic ray physics applications with KU medical and NASA.
  Link to slides of the seminar: https://www.dropbox.com/s/nw357izrktfio05/helsinki2023.pdf?dl=0
• Tuesday 8 August 2023 at 14.15 in D208: Francois Englert (Physics Nobel 2013, Université Libre de Bruxelles)      CANCELLED!
  A GLIMPSE ON THE FUTURE
  An informal discussion, chaired by Anca Tureanu, around the coffee table on gravitation and quantum mechanics, and a possible way to unlock novel grand ideas in physics.
• Tuesday 15 August 2023 at 10:15 in A315 and using Zoom:Zurab Berezhiani (Aquila, Gran Sasso)
  The Neutron Anomalies: a Portal to New Physics?
  Abstract: Some problems are mounting around neutron physics, as the neutron lifetime puzzle and the Cabibbo angle anomaly. I shall discuss possible BSM solutions of these problems and their implications for particle physics and astrophysics.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=c9cb2ebb-83ac-4034-b5b4-a5ea5363f748
• Thursday 7 September 2023 at 10:15 in A315 and using Zoom:  Ananya Tapadar (IACS Kolkata)
  
  Reconciliation of Secluded Dark Sector and Muon (g − 2) in the light of Fast Expanding Universe
  Abstract: The lack of information before Big Bang Nucleosynthesis (BBN) allows us to assume the presence of a new species φ whose energy density redshifts as  a^( −(4+n)) where n > 0 and a is the scale factor. In this non-standard cosmological setup, we have considered U(1)_(L_µ−L_τ) ⊗ U(1)_X gauge extension of the Standard Model (SM) and studied different phases of the cosmological evolution of a thermally decoupled dark sector such as leak-in, freeze-in, reannihilation, and late-time annihilation. This non-standard cosmological setup facilitates a larger portal coupling (\epsilon) between the dark and the visible sectors even when the two sectors are not in thermal equilibrium. The dark sector couples with the µ and τ flavored leptons of the SM due to the tree level kinetic mixing between U(1)_X and U(1)_(L_µ−L_τ) gauge bosons. We show that in our scenario it is possible to reconcile the dark matter relic density and muon (g − 2) anomaly. In particular, we show that for 2 × 10^(−4) < \epsilon < 10^(−3) , 5.5 MeV < m_Z’ < 200 MeV, n = 4, and 1 TeV < m_χ < 10 TeV relic density constraint of dark matter, constraint from muon (g − 2) anomaly, and other cosmological, astrophysical constraints are satisfied.
• Tuesday 19 September 2023 at 10:15 in A315 and using Zoom: Philipp Schicho (Frankfurt)
  Impact of computational diligence on GW signals from phase transitions
  Abstract: To describe cosmological phase transitions perturbatively, scale hierarchies are required. At finite temperature such a hierarchy is provided naturally for gauge theories. If this hierarchy is not accounted for, uncertainties of phase transition thermodynamic parameters can be large due to infrared sensitivities and slow perturbative convergence faced by scalar bosons.To reliably describe the phase transition thermodynamics, one can then use this hierarchy and construct a three-dimensional effective theory that systematically includes thermal resummations to all orders. Focusing on generic scalar extensions beyond the Standard Model, I determine their dimensionally reduced theory and the corresponding effective potential using the in-house software package DRalgo [1]. I present a minimal approach [2] that reconciles both gauge invariance and thermal resummation suitable for precision computations of the thermodynamic parameters of cosmological first-order phase transitions. Finally, I will address the impact of such computational diligence at the level of GW signals.[1] A. Ekstedt, P. Schicho, and T. V. I. Tenkanen, DRalgo: A package for effective field theory approach for thermal phase transitions, Comput. Phys. Commun. 288, 108725 (2023), [2205.08815].
  [2] P. Schicho, T. V. I. Tenkanen, and G. White, Combining thermal resummation and gauge invariance for electroweak phase transition, JHEP 11, 047 (2022), [2203.04284].
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=9bc7e3c8-80c2-4b02-8a4a-2144ba1d8814
• Monday 25 September 2023 at 15:15  using Zoom:  Zaryab Ahmed (Stavanger)
  Modified Kerr and Black hole ringdowns
  Abstract: In the post-merger phase of a black hole binary system, the remnant object is a perturbed black hole emitting gravitational radiation in the form of Gravitational Waves (GW) before admitting a stable state. Observations of gravitational waves can thus be used to test and constrain deviations from Einstein’s theory of gravity and the no-hair theorem, which says that only 3 parameters are required to characterize black holes; mass, spin and charge. For astrophysical purposes, only mass and spin are relevant and the black holes are described by the Kerr metric.Quasi-normal modes (QNM) have been an essential tool in studying GW events, in terms of inferring the black hole’s mass and spin. While the Kerr metric has been widely used for the analysis, a black hole can be described using a different metric. With the requirement that the metric be axisymmetric and stationary, a post-Kerr description allows for non-Kerr parameters which would violate the no-hair theorem and introduce deviations from GR results. The first task is to construct such metrics, then to compute the QNMs in this particular geometry and finally, use GW data to infer the values of the parameters. This thesis focuses on the final step to estimate the likelihood of the deviation parameter introduced by some new metric.In the post-Kerr approximation, the Johannsen-Psaltis (JP) metric admits mass, spin and ε3 as parameters where, non-zero ε3 causes deviation from the Kerr geometry. By construction, the limiting case of ε3 → 0 reproduces the Kerr metric. Glampedakis et al , outline the recipe to find QNMs in the post-Kerr approximation and consider the JP metric to find the deviations from the Kerr QNM frequency. Once the QNM spectrum of the new geometry is computed, one can use parameter estimation routines to estimate the likelihood of the parameters given the data. The author uses PyCBC inference on the ringdown stage of two GW events, GW150914 and GW190521, More interest is invested in GW190521 since it is has a higher ringdown SNR compared to GW150914 and also includes the 330 mode, implying that we have more information about the event and therefore we can find a better constraint on the deviation parameter.
• Tuesday 26 September 2023 at 10:15  in A315 using Zoom:  Merab Gogberashvili (Andronikashvili Institute of Physics, Tbilisi, Georgia)
  LIGO signals from the mirror world
  Abstract: We suggest that a major fraction of binary black holes and neutron star mergers, which might provide gravitational wave signals detectable by LIGO/VIRGO, emerged from the hidden mirror sector. Mirror particles do not interact with an ordinary observer except gravitationally, which is the reason why no electromagnetic signals accompanying gravitational waves from mergers with components composed of mirror matter are expected. Mirror matter is a candidate of dark matter and its density can exceed ordinary matter density five times. Since the mirror world is considered to be colder, star formation there started earlier and mirror black holes had more time to pick up the mass and to create more binary systems within the LIGO reachable zone. Totally we estimate a factor 10 amplification of black holes merging rate in the mirror world with respect to our world, which is consistent with the LIGO observations. If the dark matter budget of the universe is mostly contributed by the mirror particles, we predict that only about one binary neutron star (neutron star – black hole) merger out of ten detectable by LIGO/VIRGO could be accompanied by a gamma ray burst. It seems the list of candidate events recorded by LIGO/VIRGO during the third observational run supports our predictions. We consider the possibility that LIGO events GW190521, GW190425 and GW190814 may have emerged from the mirror world binaries. Theories of star evolution predict so-called upper and lower mass gaps and masses of these merger components lie in those gaps. In order to explain these challenging events very specific assumptions are required and we argue that such scenarios are orders of magnitude more probable in the mirror world.
  Link to video: https://unitube.it.helsinki.fi/unitube/embed.html?id=840974fe-5d45-4d00-9e0f-a0c61000e0ec