of the Institute of Theoretical Physics

- March 3, 2020
- Probing fifth forces with the Sun
*Dr. Ippocratis Saltas*- Central European Institute for Cosmology and Fundamental Physics, Institute of Physics, Czech Academy of Sciences
Generic extensions of General Relativity aiming to explain dark energy typically introduce fifth forces of gravitational origin. In this talk, I will explain how helioseismic observations can provide a powerful and novel tool towards precision constraints of fifth forces, as predicted by general theories for dark energy, and I will discuss the implications for cosmology.

- March 10, 2020
- On some properties of extended objects in general relativity
*Dr. Sajal Mukherjee*- Inter-University Centre for Astronomy and Astrophysics, Pune, India
I shall introduce the motion of extended objects with multipole moments occupying a finite size in space. I discuss their various interesting features along with highlighting their distinctive remarks from geodesic orbits. In particular, I shall focus on two particular events: first, orbital dynamics of spinning particles; and second, the multipole interactions between different moments, i.e., monopole, dipole or quadrupole, of the extended test particle and central object. Several other implications involving extended objects will also be mentioned in brief.

- May 12, 2020
- On Gauss-Bonnet gravity in four dimensions
*David Kubizňák*- Perimeter Institute for Theoretical Physics, Waterloo, Canada
We comment on the recently introduced Gauss-Bonnet gravity in four dimensions. We argue that it does not make sense to consider this theory to be defined by a set of D→4 solutions of the higher-dimensional Gauss-Bonnet gravity. We show that a well-defined D→4 limit of Gauss-Bonnet Gravity is obtained generalizing a method employed by Mann and Ross to obtain a limit of the Einstein gravity in D=2 dimensions. This is a scalar-tensor theory of the Horndeski type obtained by dimensional reduction methods. By considering simple spacetimes beyond spherical symmetry (Taub-NUT spaces) we show that the naive limit of the higher-dimensional theory to four dimensions is not well defined and contrast the resultant metrics with the actual solutions of the new theory. Theory and solutions in lower dimensions will also be briefly discussed.

Online seminar using Zoom. Meeting ID 969 3716 4466

Seminar will be also shown at the lecture hall of ITP. However, the capacity there will be limited to 15 people.

- May 26, 2020
- Initial data for closed conformal Killing-Yano 2-forms
*doc. Igor Khavkine, PhD.*- Department of Algebra, Geometry and Mathematical Physics, Mathematical Institute, Czech Academy of Sciences
The Kerr-NUT-(A)dS family of exactly integrable higher dimensional black hole solutions of Einstein's equations is characterized by the existence of a non-degenerate closed conformal Killing-Yano (cCYK) 2-form. Using an exhaustive search, we identify a family of 2nd order propagation identities for the cCYK equation on 2-forms in n>4 dimensions. These identities allow us to project the cCYK equations onto a spacelike surface and thus characterize the initial data for Einstein's equations whose development admits a cCYK, in analogy with the well-known Killing Initial Data that characterize developments admitting Killing vectors. This is joint work with Alfonso García-Parrado. [arXiv:1912.04752]

Seminar will be available also using Zoom.

- June 2, 2020
- Symmetries, soft theorems and amplitude reconstruction in the effective field theories
*Dr. Jiří Novotný*- IPNP
- June 9, 2020
- Symmetries, soft theorems and amplitude reconstruction in the effective field theories -- II
*Dr. Jiří Novotný*- IPNP

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