Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Seminarium "Teoria cząstek elementarnych i kosmologia"

Seminarium "Teoria cząstek elementarnych i kosmologia"

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Daniel Pinto (IFT UW)

Bubble Hydrodynamics in First-Order Electroweak Phase Transitions

Cosmological phase transitions can give rise to intriguing phenomena, such as baryogenesis or a stochastic gravitational wave background, due to nucleation and percolation of vacuum bubbles in the primordial plasma. A key parameter for predicting these relics is the bubble wall velocity, whose computation relies on solving the Boltzmann equations of the various species along the bubble profile. I will discuss how we can find this wall velocity by solving the Boltzmann equation, and how we can treat the singularities that arise in the out-of-equilibrium terms that govern the process.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Peter Matak (Comenius University in Bratislava)

From cutting rules to minimal effective theory for leptogenesis, dark matter, and neutrino masses

In the first part of the seminar, we will use unitarity and the optical theorem to build an effective theory that simultaneously explains the matter–antimatter asymmetry via leptogenesis, the dark matter relic abundance via freeze-in or freeze-out mechanisms, and neutrino masses via the Weinberg operator. We will show that, in a minimal scenario, only two new particles and a single portal operator coupling the visible and dark sectors are sufficient beyond the Standard Model. In the second part, we will focus on interpreting the non‑standard asymmetry contributions which, as we demonstrate, must be included. We will present an algorithm designed to avoid the most common mistakes and inconsistencies when calculating an asymmetry source term in the Boltzmann equation.

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Daniele Perri (IFT UW)

Magnetic monopoles as dark matter: are they still alive?

Magnetic monopoles are a long-sought prediction of Grand Unified Theories (GUTs). However, their efficient production in the early universe would result in an abundance far exceeding observational bounds — a challenge known as the cosmological monopole problem. The standard solution invokes an inflationary phase occurring after monopole formation, which dilutes their density, while removing any possibility of their present-day detection. In this talk, I will review the current status of monopoles as dark matter, demonstrating how there is still a window where even GUT monopoles can serve as viable dark matter candidates. I will also present an alternative solution to the monopole problem based on a minimal breaking of conformal symmetry in the gauge kinetic sector. The proposed mechanism enhances monopole annihilation, reducing their relic abundance to acceptable levels potentially within the reach of current and upcoming cosmic-ray detection experiments.

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Jaime Hoefken Zink (NCBJ)

Compact stars as dark matter detectors

Due to their extreme high density conditions, compact stars offer the possibility to be used as huge dark matter detectors. Surrounding dark matter may be attracted and get captured in the interior of these stars, potentially heating cold neutron stars or white dwarfs up to observable temperatures, above their expected temperature. Dark matter may also be boosted from sources like AGNs and that flux may also impact and heat compact stars.These detection mechanisms are particularly relevant for models and regions in parameter space of dark matter where direct detection experiments cannot set competitive bounds. As an example, we will present a lepton flavor violating model of fermionic dark matter, using old neutron stars as detectors. We will consider a pseudoscalar mediator (ALP) and study the process of capturing through inelastic interactions of the form: χ μ→χ e and χ e→χ μ, where χ is the dark matter fermion particle.

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Wen-Yuan Ai (Marietta Blau Institute for Particle Physics, Austrian Academy of Sciences)

Can a Gravitational-Wave Background Enhance Particle Decay?

Our Universe is permeated by both gravitational waves and matter. An intriguing question is whether a background of gravitational waves can influence particle processes in the matter sector. A particularly interesting example is the decay of dark matter, where one might naively expect a significant Bose enhancement for decay channels that emit gravitons. In this talk, I will examine how a gravitational-wave background affects particle decay by extending Weinberg’s soft theorem to situations in which a soft background is present.This talk is based on our recent work: arXiv:2510.27690.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Sebastian Trojanowski (NCBJ)

Neutrino Portals to Dark Matter: From Early Universe to Precision Cosmology

Neutrinos offer a window into beyond Standard Model (BSM) physics, and recent data prompt a re-evaluation of their role in the early universe. Neutrino portals facilitate thermal Dark Matter (DM) production, representing one of the few remaining benchmarks in the freeze-out paradigm, yet a difficult one to probe. In this talk, we first summarize constraints on such scenarios and discuss how recent and near-future cosmological data may soon illuminate these dark sectors. The latter part emphasizes the impact of resonant DM-neutrino scattering on perturbation evolution. We illustrate that incorporating these precision effects, typically associated with collider physics, significantly alters cosmological data analysis, with implications extending beyond the specific models discussed.

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Tomasz Taylor (Northeastern Univ. and Univ. Warsaw)

De S-matrix

I will discuss the properties of S-matrix describing the scattering processes of elementary particles in de Sitter spacetime

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Kamila Kowalska (NCBJ)

Quantum entanglement in perturbative scattering

I will discuss quantum entanglement in high-energy scattering of two particles characterized by an internal quantum number acting like a qubit. Working with a perturbative S-matrix, I will build the reduced density matrix of the final scattered state by tracing out the momentum degrees of freedom. In this construction, unitarity is guaranteed order by order by the optical theorem. I will present a novel analytical formula for the concurrence (qubit entanglement) of a mixed final state and show that, given an initial product state, it depends at the leading order on the real part of the inelastic forward amplitude. I will also address a recent proposal stating that some symmetries of the Lagrangian may emerge from a principle of entanglement minimization. I will show that for “flavored” scalar scattering this does not appear to be the case.

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Enrico Maria Sessolo (NCBJ)

Stabilizing dark matter with quantum scale symmetry

After reviewing a few basic notions of asymptotic safety in gravity and matter, I will show that in gauge-Yukawa theories quantum scale symmetry can prevent the appearance in the Lagrangian of couplings that would otherwise be allowed by the gauge symmetry. Such couplings correspond to irrelevant Gaussian fixed points of the renormalization group flow. Their absence implies that different sectors of the theory are secluded from one another, in similar fashion to the effects of a global or a discrete symmetry. As an example, I will impose the trans-Planckian scale symmetry on a model of Grand Unification based on the gauge group SU(6), showing that it leads to the emergence of several fermionic WIMP dark matter candidates whose coupling strengths are entirely predicted by the UV completion.

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Anish Ghoshal (IFT UW)

Inflation beyond slow roll: stochasticity, primordial black holes and scalar-induced gravitational waves

We discuss physics of inflationary cosmology beyond the assumption of standard slow-roll, and its consequences for metric perturbations leading to primordial black hole formation from large density fluctuations and first-order and second-order tensor perturbations propagating as gravitational waves. Next we will discuss how does the stochastic inflation offer a non-perturbative framework to calculate the distribution of density perturbations and in particular, large but rare fluctuations in the non-Gaussian tail of the distribution that could give rise to primordial black holes. We will discuss modelling of non-adiabatic perturbations on super-Hubble scales and we will compare the classical and stochastic delta-N formalisms used to calculate density perturbations.

Presentation based on arxiv.org/abs/2409.12950, arxiv.org/abs/2306.04002, and arxiv.org/abs/2407.15082.

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