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

Kay Schönwald (CERN)

Precise predictions for gluon fusion induced ZH production at the LHC

The associated production of a Higgs boson with a vector boson, W or Z, provides the third-largest cross section for Higgs boson production at the LHC. Furthermore, it is an important process for the measurement of the Higgs coupling to bottom quarks, which is difficult in other Higgs production processes due to large backgrounds. The process of ZH production receives contributions from a gluon-initiated subprocess, which formally enters at higher orders in QCD, but is enhanced due to the large gluon luminosity at a hadron collider. In this talk, I will present recent calculations for the 2-loop virtual amplitudes for this process valid in general kinematics, as well as the calculation of the associated 3-loop virtual amplitudes in the large top mass expansion. Afterwards, I present the public C++ library ggxy, where these corrections are implemented and which allows to freely modify all input parameters, such as the top-quark mass and its renormalization scheme and the masses of the external Z and Higgs bosons. In addition, ggxy has been interfaced to Powheg and Herwig, which allows the matching to parton showers.

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

Ignacy Nałęcz (IFT UW)

From Hydrodynamics to Bubble Wall Velocity

Cosmological scalar phase transitions are ubiquitous in particle physics models. If they are first-order, they can be tested with gravitational-wave signal and baryon asymmetry they produce. These however, crucially depend on the velocity that nucleated new-phase bubbles reached. In my talk I will present generalized description which builds a bridge between numerical simulations, often use within the community, and the analytical estimates of this parameter. Our method allows one to determine the wall velocity without the necessity of performing full real-time simulations. Moreover, I will explain why some stationary solutions discussed in the literature are not dynamically realized, and provide a selection rule determining their fate.

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

Piotr Chankowski (IFT UW)

Effective quantum field theory approach to the ferromagnetic phase transition in a gas of fermions

I will summarize our recent effective quantum field theory computations of the free energy of a gas of spin-1/2 fermions interacting through a short-range spin-independent repulsive potential. The result is used to study the impact that higher-order corrections can have on the characteristics of a phase transition to the ordered phase, namely on the emergence of itinerant ferromagnetism. I will also comment on the relation of our computations to experimental searches for the ferromagnetic transition in cold gases of fermionic atoms.

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Zapraszamy na spotkanie o godzinie 12:15

Zahra Tabrizi (University of Pittsburgh)

[ON-LINE] Neutrino-Collider Synergy for Beyond the Standard Model Searches

Neutrinos were discovered more than 60 years ago, yet they are the most mysterious particles of the Standard Model (SM) of particle physics. In order to further explore the neutrino sector, next-generation, long-baseline neutrino oscillation experiments are being built, including the DUNE and Hyper-K experiments. Given the intense neutrino beam, the massive fardetector, and the envisaged scale of the near detector, these experiments will certainly offer a rich physics program. In this seminar I aim to explain how we can search for physics beyond the Standard Model (BSM) at neutrino experiments and unify neutrino and collider information in new physics searches within single, quantitative frameworks. I will first give a general introduction on the current status of neutrino physics. Then I will discuss how we can search for new particles and/or interactions at neutrino experiments with the goal of combining the results with the ones of colliders. I will explain how this can be done via two complementary approaches, 1) Direct search of dark sectors, where I will use these experiments for searches of specific new particles, including light dark matter or axion-like particles, etc; 2) Indirect search of new physics, where I will demonstrate how to use the systematic framework of Effective Field Theory at neutrino experiments, where the results can be combined with the results of other low or high energy experiments, such as the LHC. Finally, I will discuss future collider prospects, such as neutrino physics at a muon collider.
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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Patrick Foldenauer (IFT-UAM CSIC, Madrid)

Testing New Physics with Neutrinos at Dark Matter experiments

In this talk, I will present a new avenue of how to test new physics with neutrinos - the observation of (solar) neutrino scattering in dark matter direct detection experiments. It will be the first time coherent elastic neutrino-nucleus scattering (CEvNS) will be detected from astrophysical neutrinos, as opposed to reactors or spallation sources. Simultaneously, it will provide a complementary measurement of solar neutrinos via elastic neutrino-electron scattering. I will review the implications of this novel signal both for neutrino physics within and beyond the Standard Model. In this context, I will also discuss the prospects of observing solar neutrino scattering with RES-NOVA, a novel cryogenic bolometer experiment designed to observe CEvNS of astrophysical neutrino sources.

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

Daniele Rizzo (NICPB Tallinn)

Exact Renormalization Group methods in Particle Physics and Quantum Gravity

In this talk, I will give an overview of Exact Renormalization Group techniques and apply them to the study of fixed points in Beyond the Standard Model (BSM) theories coupled to Quantum Gravity (QG). I will begin by motivating the need for non-perturbative physics and introducing the renormalization group idea proposed by Wilson. Structural differences between the Wilsonian proper-time and Wetterich flow equations will be highlighted, with the former being the main focus of the talk. Following Phys. Rev. D 113, 045020 (2026), I will discuss the perturbative structure of the proper-time renormalization group flow. Although the proper-time flow does not belong to the class of exact functional renormalization group equations, we show that it correctly reproduces the universal coefficients of the $\beta$-functions of $O(N)$ and Yang–Mills theories at one and two loops. I will highlight several attempts to compute these coefficients using the Wetterich equation and discuss the differences between the Wetterich approach and the proper-time flow equation. These results show that, despite its limitations in reconstructing the full effective action, the proper-time flow retains the essential universal content of renormalization, explaining its reliability in many applications. One of the main applications of non-perturbative techniques is the computation of fixed points in Quantum Gravity within the framework known as Asymptotic Safety. I will show how the presence of a fixed point in the running of QG couplings can generate a fixed point for BSM couplings, thereby providing insights into the values of BSM couplings at energy scales relevant for collider physics. Finally, I will apply the proper-time flow equation to the running of the simplest QG model, Einstein–Hilbert gravity, and study the gauge and regulator dependence of the fixed point of this theory when coupled to the Standard Model.

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

Fotis Koutroulis (IHEP Beijing)

Cosmological Gravitational Particle Production: Sterile Neutrinos as Dark Matter candidates

In this work we consider cosmological gravitational production of Dirac sterile neutrinos as dark matter candidates during and after inflation. In the former, the Higgs field experiences large quantum fluctuations driving its average field value to the Hubble scale and above facilitating the sterile neutrino production. However, the production efficiency due to classical gravity still remains suppressed compared to the standard freeze-in mechanism. Quantum gravitational effects, on the other hand, are expected to break conformal invariance of the fermion sector by the Planck scale-suppressed operators irrespective of the mass. We find that such operators are very efficient in fermion production immediately after inflation, generating a significant background of stable or long-lived feebly interacting particles. This applies, in particular, to sterile neutrinos which can constitute cold non-thermal dark matter for a wide range of masses, including the keV scale.

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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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