"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024
2024-03-14 (Thursday)
room 1.01, Pasteura 5 at 12:15 
Matteo Fael (CERN)New numerical methods for Feynman integrals and their applications to B meson decays
The method of differential equations has become the standard avenue in the evaluation of multi-loop Feynman integrals. However for problems where so-called elliptic sectors appear, a general algorithm for solving analytically the differential equations has not been established yet. A numerical solution may be attempted nevertheless for Feynman integrals depending on few kinematic parameters. In this seminar I will review methods recently developed to numerically compute multi-loop integrals depending on one dimensionless scale. Such numerical approaches provide results well suited for fast numerical evaluation and sufficiently precise for phenomenological studies. I will discuss the application to the calculation of the higher order QCD corrections to B-meson decays.
2024-03-07 (Thursday)
room 1.01, Pasteura 5 at 12:15
Zurab Berezhiani (University of L'Aquila)Extremely energetic cosmic rays: a signal to new astro/particle physics
The identities and sources of extremely energetic cosmic rays (EECR) with E > 50-100 EeV remains a mystery. Situation is paradoxical because there are many controversies in the EECR observations by different experiments. I propose a possibility to explain all these tensions suggesting that the dark matter of the universe is represented by a parallel mirror sector of particles, ordinary and mirror neutrinos and neutrons have a mixing, and characteristic time of n-n' oscillation is smaller than the neutron decay time (this is not excluded neither by the present experiments nor by the astrophysical bounds). I shortly discuss also some other phenomenological and cosmological implications of this scenario.
2024-02-29 (Thursday)
room 1.01, Pasteura 5 at 12:15
Dibyakrupa Sahoo (IFT UW)CP violation in Higgs sector (A phenomenological and first principle overview)
In the SM the Higgs boson is a scalar (CP-even) particle. Currently the 125 GeV Higgs boson is consistent with such a characterization. However, experimentally it is still possible to have some CP-admixture leading to CP violation in the Higgs sector. In this talk, we will see how from first principles one can make connections among the various CP violation possibilities, and how the observables have an underlying connection. Taking a specific example of Higgs-tau-tau Yukawa interaction, I will highlight these aspects, and show an interesting new possibility of utilizing Dalitz plot distribution to probe CP violation. This complementary methodology can play an important role in future explorations of CP violation in Higgs sector.
2024-01-25 (Thursday)
room 1.01, Pasteura 5 at 12:15
Michał Ryczkowski (IFT UW)SmeftFR v3 - a tool for creating and handling vertices in SMEFT to the 1/Λ^4 order in the EFT expansion
SmeftFR v3 [Comput.Phys.Commun. 294 (2024) 108943, 2302.01353, https://www.fuw.edu.pl/smeft/] is a publicly available code that enables derivation of Feynman rules for interaction vertices from the dimension-5, dimension-6, and (so far) all bosonic dimension-8 SMEFT operators. Obtained Feynman rules allow for consistent numerical (e.g. in MadGraph) or symbolic (e.g. in FeynArts, FeynCalc, FormCalc) calculations in SMEFT to the 1/Λ^4 order in the EFT expansion, including dimension-6 squared and dimension-8 terms, which is a novelty in the literature. In my talk, I will discuss some of the most important new features of SmeftFR v3, such as choosing among and using one of the predetermined input schemes, including one for the CKM matrix. I will also provide practical examples of usage of the code and describe some of its possible applications.
slides: https://mycloud.fuw.edu.pl/index.php/s/xFgg7XXzJg3XYzF
2024-01-18 (Thursday)
room 1.01, Pasteura 5 at 12:15
Wojciech Kamiński (IFT UW)Quantum stress-energy tensor
I will describe a construction of the quantum stress-energy tensor for a free scalar field on a curved background. There exist various versions, not all completely satisfactory. Situation is even more interesting on the FRW background where additionally mode summation can be used. The mode summation method and the methods for general spacetimes do not have much relation on a first sight. However, this impression is misleading.
slides: https://mycloud.fuw.edu.pl/index.php/s/cEBpzaJi6oejeLE
2024-01-11 (Thursday)
room 1.01, Pasteura 5 at 12:15
Nicholas Orlofsky (IFT UW)Origin of nontopological soliton dark matter
Nontopological solitons with large global charges and masses, even above the Planck scale, can form in the early universe and dominate the dark matter abundance. In solitosynthesis, solitons prefer to grow as large as possible under equilibrium dynamics when an initial global charge asymmetry is present. Their abundance is set by when soliton formation via particle fusion freezes out, and their charges are set by the time it takes to accumulate free particles. I discuss improvements to the estimation of both quantities, and in particular show that much larger-charged solitons form than previously thought. The results are estimated analytically and validated numerically by solving the coupled Boltzmann equations. Without solitosynthesis, phase transitions can still form solitons from particles left inside false-vacuum pockets and determine their present-day abundance and properties. Even with zero charge asymmetry, solitons formed in this way can have very large charges on account of statistical fluctuations in the numbers of (anti)particles inside each pocket.
2023-12-21 (Thursday)
room 1.01, Pasteura 5 at 12:15
Piotr Toczek (IFT UW)Primordial black holes from strong first order phase transitions
This talk is aimed to analyze the possibility of Primordial Black Holes (PBHs) production during supercooled first order phase transitions in the Early Universe. The transition proceeds through the nucleation of bubbles of the broken phase in an initial background of the symmetric phase, which later collide and percolate, finishing the conversion of the Universe, with their nucleation rate assumed to be given by generic action expanded to the quadratic order. We focus on a scenario in which PBHs are produced purely by the collapse of overdense regions which remain long enough in the false vacuum state, where bubble nucleation is effectively postponed. We present a description of such regions and determine the conditions of their gravitational collapse.We find the final mass function and abundance of PBHs created in such manner to be highly dependent on the history of the transition and we identify the regions in parameter space for which PBHs' abundance matches that of Dark Matter inferred from observations.
slides: https://mycloud.fuw.edu.pl/index.php/s/nrJoY7magtEnKtX
2023-12-14 (Thursday)
room 1.01, Pasteura 5 at 12:15
Roberto Franceschini (Rome III)Future Colliders
In this talk I will review the motivations for further exploration of the physics at the shortest distances. I will review the role that particle collider can play in future advances on the open issues of the Standard Model of particle physics. I will also briefly introduce the collider projects currently under discussion to push the energy frontier after the High-Luminosity LHC and the highlights of the physics that can be carried out at each machine.
slides: https://mycloud.fuw.edu.pl/index.php/s/NrcJLrTx5mC7T8k
2023-12-07 (Thursday)
room 1.01, Pasteura 5 at 12:15
Fotis Koutroulis (IFT UW)Phases of Pseudo-Nambu-Goldstone Bosons
In this talk I will focus on the study of the vacuum dynamics of pseudo-Nambu-Goldstone bosons (pNGBs) for SO(N+1) —> SO(N) spontaneous and explicit symmetry breaking. I will show how to determine the magnitude of explicit symmetry breaking consistently with an EFT description of the effective potential at zero and finite temperatures. Given that, I will expose and clarify novel additional vacuum transitions that can arise for generic pNGBs below the initial scale of SO(N+1) —> SO(N) spontaneous symmetry breaking, which may have phenomenological relevance. In this respect, two phenomenological scenarios are analyzed: thermal and supercooled dark sector pNGBs. In the thermal scenario the vacuum transition is first-order but very weak. For a supercooled dark sector we find that, depending on the sign of the explicit symmetry breaking, one can have a symmetry-restoring vacuum transition SO(N-1) —> SO(N) which can be strongly first-order, with a detectable stochastic gravitational wave background signal.
slides: https://mycloud.fuw.edu.pl/index.php/s/q2pCCCQkiJk2Dim
2023-11-30 (Thursday)
room 1.01, Pasteura 5 at 12:15
Marco Piva (IFT UW)High-Energy Behavior of Scattering Amplitudes in Theories with Purely Virtual Particles
A certain class of renormalizable quantum field theories with purely virtual particles, including quantum gravity, exhibits undesired behaviors, typical of nonrenormalizable theories, and seems to violate positivity bounds. In particular, cross sections can grow as powers of the center-of-mass energy squared. In this talk we argue that the problem should be viewed as a violation of perturbativity, instead of unitarity. Indeed, we show that nonperturbative techniques, such as resummation of self energies, fixes the issue. As an explicit example, we consider a class of O(N) theories, which can be studied exactly to the leading order in the large-N expansion. We show that, after the resummation, the cross sections correctly decrease as inverse powers of the center-of-mass energy squared and that the amplitudes satisfy unitarity. These results are compared to theories with ghosts, where the resummation does not help in improving the high-energy behavior, and to nonrenormalizable theories. Finally, the appearance of new resonances or bound states is discussed.
slides: https://mycloud.fuw.edu.pl/index.php/s/wbQbJP5SzcZiZa7