Nordic Winter School on Particle Physics and Cosmology 2022

5 Feb 2022, 08:00 → 10 Feb 2022, 20:00 Europe/Copenhagen

Thon Hotel Skeikampen

 

Nordic Winter School on Particle Physics and Cosmology

Nordic Winter School aims to introduce Ph.D. and advanced Master's students to current exciting topics in particle physics and cosmology, and take place at the Thon Hotel Skeikampen, approximately 40 kilometers north of Lillehammer (200 km north of Oslo). You can find details about the area here.

This year, the school has a particular focus on gravitational physics and the science behind gravitational wave analysis and will feature the following four lectures

•  Maria Haney (4 hrs) LIGO-Virgo Science and Results with Forecasting on Future GW Instruments
•  Adam Pound (4 hrs) Self-Force Theory and LISA 
•  David Kosower (4 hrs) Classical Gravity from Quantum Scattering
•  Michèle Levi (4 hrs) From QFT to Real-World Gravity

Together with the four special lectures:

• Henrik Johansson (1 hr) Double Copy and Higher-Spin Amplitudes
• Niels Obers (1 hr) Non-relativistic gravity
• Alex B. Nielsen (1 hr) Perturbing black holes

Funding and planning committee: N. Emil J. Bjerrum-Bohr, Poul H. Damgaard, Henrik Johansson, Michèle Levi, Niels Obers. 

Practical organisation, chairing of talks and coordination and organisation of the student talk program: Robin Marzucca, Alex Nielsen, Anne Spiering, Cristian Vergu

Student assistant: Marie Ernø-Møller

The school is limited to approximately 25 students from Nordic countries and is subject to a selection. We expect to be able to cover all local costs + transportation between Oslo Airport and the hotel. Young post-docs are encouraged to participate as well. Exceptionally talented M.Sc. students can apply too.

Exceptionally qualified students from outside the region may be admitted on a case by case basis, and on the assumption that they can have their expenses covered by other sources.

Feb Saturday 5th and Thursday 10th will be days of travel, and bus transportation will be arranged from/to Oslo Airport Gardermoen on these dates. If you're accepted at the school, you should plan to catch the bus at 2:00 PM on Feb 5th and have a return flight no earlier than 1:00 PM on the 10th. Lectures will be held on Sunday through Wednesday, with free time in the middle of the day for outdoor activities like cross-country and downhill skiing. 

The school is supported financially by NORDITA, the Niels Bohr Institute, the Niels Bohr International Academy, the Niels Bohr Institute Foundation, the Copenhagen University Faculty of Science, the Villum Foundation, the Carlsberg Foundation and the EU Marie Curie SAGEX ETN network.

 

 

Sunday, 6 February

1 Pound Lecture 1: gravitational wave astronomy, the two-body problem, and self-force theory

Gravitational wave astronomy: present and future
Gravitational self-force theory

Speaker: Adam Pound

Pound_Nordic_school_L1.pdf

2 Pound Lecture 2: the local problem: how to deal with small bodies

Perturbation theory in GR
Small bodies and punctures
Point particles and mode-sum regularization Regularization via Green’s functions
Point particles beyond linear order

Speaker: Adam Pound

Nordic_school_L2.pdf

3 Pound Lecture 3: the global problem: orbital dynamics in Kerr

Geodesic motion in Kerr
Perturbed motion in Kerr
Transient resonances

Speaker: Adam Pound

Nordic_school_L3.pdf

4 Haney Lecture 1:

Speaker: Maria Haney

5 Haney Lecture 2:

Speaker: Maria Haney

6 How perturbative QCD constrains the Equation of State at Neutron-Star densities

The rapid evolution of neutron-star astronomy in recent years is for the first time giving us empirical access to the physics of the cores of neutron-stars, the internal structure of which is determined by the equation of state (EoS) of strongly interacting matter. In this talk I demonstrate in a general and analytic way how high-density information about EoS of strongly interacting matter obtained using perturbative Quantum Chromodynamics constrains the same EoS at densities reachable in physical neutron stars. The results can be used to propagate the pQCD calculations reliable around 40ns to lower densities (starting from 2.2 ns) in the most conservative way possible. These purely theoretical results are independent of astrophysical neutron-star input and hence they can also be used to test theories of modified gravity and BSM physics in neutron stars.

Speaker: Oleg Komoltsev

7 Stochastic inflation from QFT and the parametric dependence of the effective noise amplitude

During inflation, quantum field fluctuations are placed in squeezed states which undergo quantum-to-classical transitions on super-Hubble scales, in the sense that the non-commutative parts of the fields then become small compared to their anti-commutative parts. An effective theory for the physics of the long-wavelength parts of quantum scalar fields in the super-Hubble regime is the stochastic inflation formalism. In this framework, the non-linear dynamics of the long-wavelength perturbations may be phrased in terms of an effective classical, but stochastic evolution equation. The stochastic noise represents short-wavelength modes which continually redshift into the long-wavelength domain during the inflationary expansion. Long-wavelength observables can be computed from a corresponding Fokker-Planck equation, and has been shown to reproduce the correct IR behaviour of the full QFT statistical propagator to leading order in the coupling. This has made stochastic inflation a popular resummation method in the cosmological context, yet its range of validity compared to other QFT methods remain unclear. In this talk I will discuss some recent progress related to how the stochastic dynamics may be derived from first-principles QFT in an expanding background through a sequence of approximations.

Speaker: Magdalena Eriksson

8 From Non-relativistic to Post-Newtonian Gravity

In recent years a covariant 1/c-expansion of general relativity, known as non-relativistic gravity, has been developed. This new expansion has many interesting prospects but much is still unknown about it. One thing that remains unclear is what connection, if any, it has to the post-Newtonian approximation. So far, Non-relativistic gravity is believed to be a more general approximation that under certain simplifying assumptions becomes equivalent to the post-Newtonian approximation. In the talk I will explain why this is believed to be true and I will describe some of the efforts that my supervisor Jelle Hartong and I are making to validate this. Furthermore, I will discuss how non-relativistic gravity might be able to improve upon certain aspects of the post-Newtonian approximation if a connection between them is made.

Speaker: Jørgen Musaeus

9 Carrollian and celestial spaces at infinity

I will discuss how the geometry of the asymptotic infinities of 4-dimensional Minkowski spacetime is captured by homogeneous spaces of the Poincaré group. In addition to the blowups of spatial (Spi) and timelike (Ti) infinities a la Ashtekar-Hansen, which are (pseudo-)carrollian geometries, this construction naturally leads to a novel space Ni that fibers over scri and is equipped with a doubly-carrollian structure. All these spaces embed into a 6-dimensional pseudo-euclidean space of signature (-,-,+,+,+,+), which generalises a similar construction for Minkowski space by Penrose and Rindler. Finally, I will discuss how these geometries can be made dynamical via a gauging procedure.

Speaker: Emil Have

Monday, 7 February

10 Pound Lecture 4: the global problem: black hole perturbation theory

Multiscale expansion of the field equations
Results at 0PA order
Results at 1PA order

Speaker: Adam Pound

Nordic_school_L4.pdf

11 Haney Lecture 3:

Speaker: Maria Haney

12 Haney Lecture 4:

Speaker: Maria Haney

13 Kosower Lecture 1:

Speaker: David Kosower

Classical Gravity from Quantum Scattering Amplitudes - Lecture I - as delivered.pptx

14 Kosower Lecture 2:

Speaker: David Kosower

Classical Gravity from Quantum Scattering Amplitudes - Lecture II - as delivered.pptx

15 Higher spin formalisms

Motivated by higher spin scattering amplitudes in gravity, we review and compare the interactions of higher spin fields in different formalisms

Speaker: Rasmus Strid

16 Understanding causality in the effective field theory of gravity

Effective field theory (EFT) is a theory-agnostic approach to understanding how high-energy phenomena would manifest in our low-energy universe. It is an expansion in higher-dimension operators built out of light fields with unknown coefficients. These coefficients can either be constrained through experiment or by demanding consistency with theoretical expectations, such as causal wave propagation. In dynamical gravitational EFTs, where there is no globally defined lightcone, defining causality is a nuanced problem. In this talk, using Gauss-Bonnet gravity as an example, I will explain why the recently introduced "infrared" causality is the correct criterion for determining consistency of low-energy EFTs. The crucial ingredient will be properly identifying the "regime of validity" of the EFT expansion, and recognising that it is only sensible to ask whether it is causal within that regime. Based on arXiv:2112.05031.

Speaker: Aoibheann Margalit

17 Resonances, black hole mimickers and the greenhouse effects: consequences for gravitational-wave physics

Ultracompact objects with photonspheres are known to mimic many observational features of black holes. It has been suggested that anomalous tidal heating or the presence of resonances in gravitational-wave signals would be a clear imprint of a surface or the absence of a horizon. Such claims and studies are all based on a frequency-domain analysis, assuming stationarity. In this talk, we will see that the object needs to first “fuel-up” until it reaches the stationary regime. The presence of a stable light ring and large light-travel times inside the object may in fact delay enormously the “charging-up” and effectively contribute to the effacement of structure. In other words, black hole mimickers behave as black holes more efficiently than previously thought. Our results have implications for other resonant systems with sharp resonances, including “floating orbits” around spinning black holes.

Speaker: Francisco Duque

Tuesday, 8 February

18 Levi Lecture 1:

Speaker: Michèle Levi

nordicschool.pdf

19 Levi Lecture 2:

Speaker: Michèle Levi

20 Levi Lecture 3:

Speaker: Michèle Levi

21 Obers Lecture 1:

Speaker: Niels Obers

Skeikampen_lecture_2022.pdf

22 Johansson Lecture 1:

Speaker: Henrik Johansson

Skeikampen2022_HJ.pdf

23 Double copy and massless free fields in curved spacetime

Assuming any massless free-fields with spin higher than 1/2 are constructed by scalar fields (spin-0) and Dirac-Weyl fields (spin-1/2), we introduce a map between spin-2 massless free-fields (gravity fields) and Dirac-Weyl fields in spinor formalism, then associated Dirac-Weyl spinors that can live in certain spacetime are identified. Regarding them as basic units, other higher spin massless free-fields are built. In this way, some hidden fundamental features related to massless-free fields are revealed. In particular, we systematically rebuild the double copy for type N and type D spacetime. We further extend the study to vacuum non-twisting type III solutions, we find there is a special Dirac-Weyl scalar whose square is just proportional to Weyl scalar, then a degenerate Maxwell field is constructed with the aid of an auxiliary scalar field, both fields not only satisfy their field equation in the curved background spacetime, but also in flat spacetime. The result further confirms that there must exist a deep connection between gravity theory and Yang-Mills gauge theory.

Speaker: Han Shanzhong

24 Kerr Black Holes and Higher-Spin Compton Scattering

Quantum scattering amplitudes for massive matter have received new attention in connection to classical calculations relevant to gravitational-wave physics. Amplitude methods and insights are now employed for precision computations of observables needed for describing the gravitational dynamics of bound massive objects such as black holes. An important direction is the inclusion of spin effects needed to accurately describe rotating (Kerr) black holes. Higher-spin amplitudes introduced by Arkani-Hamed, Huang and Huang at three points have by now a firm connection to the effective description of Kerr black-hole physics. The corresponding Compton higher-spin amplitudes remain however an elusive open problem. Here we draw from results of the higher-spin literature and show that physical insights can be used to uniquely fix the Compton amplitudes up to spin 5/2, by imposing a constraint on a three-point higher-spin current that is a necessary condition for the existence of an underlying unitary theory. We give the unique effective Lagrangians up to spin 5/2, and show that they reproduce the previously-known amplitudes. For the multi-graviton amplitudes analogous to the Compton amplitude, no further corrections to our Lagrangians are expected, and hence such amplitudes are uniquely predicted. As an essential tool, we introduce a modified version of the massive spinor-helicity formalism which allows us to conveniently obtain higher-spin states, propagators and compact expressions for the amplitudes.

Speaker: Paolo Pichini

25 SUSY in the sky with gravitons

The worldline quantum field theory (WQFT) formalism describes classical gravitational observables including spin effects up to quadratic order in the multipole expansion, and including finite-size corrections. The theory enjoys an N=2 worldline supersymmetry between spin and position degrees of freedom. Recently we have used the WQFT to compute gravitational observables at third Post-Minkowskian (PM) order including quadratic-in-spin effects and radiation-reaction effects. I will discuss this spinning WQFT and our recent 3PM results. I will also consider how our approach is related to other approaches currently used in the PM expansion.

Speaker: Gustav Jakobsen

Wednesday, 9 February

26 Levi Lecture 4:

Speaker: Michèle Levi

27 Kosower Lecture 3:

Speaker: David Kosower

28 Kosower Lecture 4:

Speaker: David Kosower

29 Nielsen Lecture 1:

Speaker: Alex Nielsen