Faculty of Physics University of Warsaw > Events > Seminars > "High Energy, Cosmology and Astro-particle Physics (HECA)" Seminar

"High Energy, Cosmology and Astro-particle Physics (HECA)" Seminar

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join us at 11:15

(Tohoku University)

Primordial black hole formation by inverted bubble collapse

Kodai Sakurai

ONLINE SEMINAR !!!

https://uw-edu-pl.zoom.us/j/5613854348

A primordial black hole (PBH) is one of the promising candidates for dark matter. PBHs can form when significant density perturbations are generated in the early Universe. Various mechanisms for producing overdense regions that lead to PBH formation have been proposed in the literature. Many of these mechanisms postulate that such an overdense region has spherical symmetry; however, in general, deviations from a perfect sphere can occur, making PBH formation nontrivial. In this talk, we discuss a novel mechanism for PBH formation in which the generated overdense region maintains spherical symmetry. We also demonstrate that the observed microlensing events in the OGLE and Subaru HSC data can be explained by applying this new mechanism to extended Higgs models.

room B2.38, Pasteura 5 at 11:15

Andreas Trautner (CFTP, IST, University of Lisbon)

Electroweak scale hierarchy from conformal and custodial symmetry

I will introduce the idea of "Custodial Naturalness" to explain the origin of the electroweak scale hierarchy. Custodial Naturalness is based on classical scale invariance as well as an extension of the Standard Model (SM) scalar sector custodial symmetry to SO(6). This requires a single new complex scalar field charged under a new U(1) gauge symmetry which partially overlaps with B-L. Classical scale invariance and the high-scale scalar sector custodial symmetry are radiatively broken by quantum effects that generate a new intermediate scale by dimensional transmutation. The little hierarchy problem is solved because the Higgs boson arises as pseudo-Nambu-Goldstone boson of the spontaneously broken SO(6) custodial symmetry. The minimal realization of Custodial Naturalness has the same number of parameters as the SM and predicts testable new physics in the form of a heavy Z' as well as a light but close-to invisible dilaton. Simple extensions furthermore allow to explain neutrino masses and Dark Matter - only in a region of parameter space that can be completely excluded by future colliders.

room B2.38, Pasteura 5 at 11:15

Mark Goodsell (LPTHE, Paris)

Seeking an explanation of compressed spectrum excesses at the LHC

ATLAS and CMS have conducted two pairs of broadly equivalent analyses, and find excesses in all four cases. This consists of searches for soft leptons (originally in supersymmetric models with compressed spectra) and monojets. I will describe my recent work on trying to interpret these excesses, and quantify their significance, in terms of both supersymmetric and non-supersymmetric models, and to tie them to other observations such as dark matter.

room B2.38, Pasteura 5 at 11:15

Maxim Laletin (University of Warsaw)

Revisited axion contribution to dark radiation using momentum-dependent evolution

Axions can be produced via the interactions in the thermal plasma of the early Universe and their contribution to dark radiation can modify the cosmological observables and constrain the axion couplings to SM particles. In my talk I am going to outline an approach to calculate the axion cosmological abundance that goes beyond the approximations widely used in the literature on the topic and demonstrate how it affects the bounds on axion couplings on the example of axion interactions with leptons.

room B2.38, Pasteura 5 at 11:15

Tomasz Krajewski (CAMK, Warsaw)

How to calculate the terminal velocity of a bubble wall?

Cosmological first order phase transitions are intriguing processes with rich phenomenological consequences. They proceed via nucleation of bubbles containing energetically favorable phase in the background of the metastable phase. Such bubbles expand due release of the latent heat, but can be slowed down and even reach the constant subliminal velocity by interactions with the plasma of (not necessarily Standard Model) particles. The terminal velocity determines phenomenological consequences of the transition, since faster walls emit stronger gravitational waves, while slower walls are expected to produce the higher matter-antimatter asymmetry in scenarios of the electroweak baryogenesis, but is much harder to predict than other parameters of the transition. Even though, a significant effort has been undertaken by the community to calculate the velocity from first principles, the final conclusion was still not clear. The recent progress in this field, both numerical and analytical, will be reported in this talk.

room B2.38, Pasteura 5 at 11:15

Priyanka Lamba (Università di Bologna)

Quantum properties of H->VV: precise predictions in the SM and sensitivity to new physics

The CMS and ATLAS experiments have recently confirmed spin entanglement in top-antitop pairs at high-energy colliders, inspiring further exploration of other processes. This talk addresses the sensitivity of quantum observables in the H->VV process. We study Higgs boson decays into vector bosons in four-lepton final states, calculating quantum observables within the Standard Model up to next-to-leading order (NLO) in electroweak couplings. Our results show that NLO corrections significantly modify quantum correlation patterns relative to tree-level predictions. Additionally, we analyze the effects of potential new physics in both Higgs couplings to four leptons and modifications to the H->VV vertex on quantum observables.

room B2.38, Pasteura 5 at 11:15

Peter Matak (Comenius University, Bratislava)

Feynman rules for the Boltzmann equation

In the first part of the seminar, we focus on unitarity and optical theorem and their relation to quantum kinetic theory. Using the holomorphic modification of cutting rules, we demonstrate that even when starting with zero-temperature Feynman rules and classical phase-space densities, thermal mass and quantum statistical effects inconspicuously enter the Boltzmann equation. The second part will then focus on calculating reaction rate CP asymmetries necessary to source the matter-antimatter asymmetry according to Sakharov's conditions. It will be shown how the direct use of unitarity allows for tracking the asymmetry cancellations in a purely diagrammatic way.

room B2.38, Pasteura 5 at 11:15

Marco Merchand (KTH Stockholm)

Probing Strong Dynamics and Phase Transitions: Gravitational Wave Signatures in a Maximally Symmetric Composite Higgs Model

In this work we explore a maximally symmetric composite Higgs model featuring a next-to-minimal coset structure, where a pseudoscalar singlet arises alongside the Higgs doublet. Maximal symmetry ensures a finite radiative scalar potential, allowing for a detailed study of electroweak phase transitions in the presence of explicit CP violation. We explore the implications of a CP-violating source in the strong sector, which induces a Z2-asymmetric scalar potential and leads to a non-zero vacuum expectation value for the singlet. After incorporating finite temperature corrections and imposing constraints from current LHC bounds and electric dipole moment measurements, we find that the explicit CP violation drives a strong first-order phase transition. We illustrate that these phase transitions produce gravitational wave signatures that could be observable at future detectors, offering a novel approach to probing composite Higgs models beyond collider experiments. This work highlights the potential of gravitational waves as complementary probes of the strong dynamics in new physics scenarios.

room B2.38, Pasteura 5 at 11:15

Krzysztof Jodłowski (Institute for Basic Science, Daejeon, S Korea)

Clockwork inspired extra dimension models at future lepton colliders, beam dumps, and SN1987

Generalized Continuum Clockwork (GCC) is an extra-dimensional generalization of the clockwork mechanism dynamically generating hierarchical couplings and mass scales. We study three benchmark geometries of GCC: the Randall-Sundrum (RS) model with a warped extra dimension, linear dilaton background, and a generalized linear dilaton model with a novel Kaluza-Klein (KK) graviton structure. We investigate the prospects of searching for signatures of CCW models at current and future colliders like the LHC, CLIC, and FCC-ee using visible decays of KK gravitons and the radion. We also explore the long-lived regime of these states at beam dump experiments like Belle II, FASER2, MATHUSLA, and SHiP, as well as constraints from astrophysical and cosmological observations. We find that combining both kind of searches will enable comprehensive coverage of the relevant CCW parameter space. Finally, we update the prospects of the RS with a third, dark brane, which was proposed as a potential origin of the NANOGrav gravitational wave signal from a first-order phase transition.

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