"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024
2022-03-10 (Thursday)
room 1.01, Pasteura 5 at 12:15 
Ayuki Kamada (IFT UW)Dark hadrons and intensity/lifetime frontier experiments
There may exist a collection of particles, which have different dynamics from SM particles and interact with SM particles only feebly through a portal particle, e.g., dark photon. Such an idea, called a dark sector, has been attracting growing interests, since dark matter may reside in a dark sector. Intensity/lifetime frontier experiments search for visible decay of long-lived dark sector particles. Specific plans are searches with forward (FASER) and off-axis (MATHUSLA) detectors at high-luminosity LHC, and with a new detector (DarkQuest) at the Fermilab SeaQuest experiment. They may provide an intriguing possibility to probe a GeV-scale dark confining dynamics. Some of associated dark hadrons are good dark matter candidates, e.g., strongly interacting massive particles and asymmetric dark matter, while others decay into SM particles with a long lifetime. We discuss the sensitivity of the near-future intensity/lifetime frontier experiments to dark hadrons.
2022-03-03 (Thursday)
room 1.01, Pasteura 5 at 12:15
Sebastian Trojanowski (NCBJ)Beyond the Standard Model physics and far-forward region of the LHC
CANCELLED
2022-01-27 (Thursday)
join us at 12:15
Rafał Masełek (IFT UW)Discovery prospects for long-lived highly electrically charged particles at the LHC
In recent years studies of long-lived charged particles predicted by some BSM scenarios attracted more attention. We present a highly model independent study targeting colour-singlet and colour-triplet particles, with electric charges up to 8 times the elementary charge. In our work, we assess the possibility to detect such particles during Run-3 and at HL-LHC, by estimating the sensitivity of MoEDAL and ATLAS detectors. We present for the first time the expected upper mass limits for highly charged LLPs.
slides: https://mycloud.fuw.edu.pl/index.php/s/3Mn92gEnGEiXKG9
2022-01-20 (Thursday)
join us at 12:15
Marek Lewicki (IFT UW)Search for new physics through primordial gravitational waves
We are currently witnessing the dawn of a new era in astrophysics and cosmology, started by the LIGO/Virgo observations of gravitational waves. These signals also open a new window into processes taking place in the first moments of our Universe. This is due to the fact that GWs propagate freely from the moment of their production unlike like photon based signals which can only propagate freely since the Universe became transparent due to recombination. I will discuss prospects for GW detection with the next generation of experiments. Including the problems connected with observation of a primordial signal in the presence of a foreground produced much more recently by astrophysical objects. The specific early Universe sources I will focus on are cosmological first order phase transitions and cosmic string networks. I will also discuss to what extent we can probe the expansion of the Universe using these primordial GW signals.
slides: https://mycloud.fuw.edu.pl/index.php/s/6t2B3s3gdaFy564
2022-01-13 (Thursday)
join us at 12:15
Lukas Witkowski (Institut d’Astrophysique de Paris CNRS — Sorbonne Université)Probing inflation at small scales with the stochastic gravitational wave background
The period of cosmic inflation is typically tested through its predictions for the Cosmic Microwave Background and the large-scale structure of our universe. However, these observational channels are only sensitive to a part of the inflationary era, while a significant part remains experimentally inaccessible. In this talk I will explain how the nascent field of gravitational wave astronomy can shed light on this so far “dark” phase of inflation. In particular, I will show that departures of inflation from the single-field slow-roll paradigm, motivated by ultraviolet completions of inflation, lead to a characteristic oscillation in the stochastic gravitational wave background. The properties of these oscillations encode information about the departure from single-field slow-roll, thus providing insight on the mechanism behind inflation. I will also comment on the prospects of observing this oscillatory signal with upcoming gravitational wave observatories such as LISA.
slides: https://mycloud.fuw.edu.pl/index.php/s/gyHrfM8aJertkic
2021-12-16 (Thursday)
join us at 12:15
Aqeel Ahmed (MPI for Nuclear Physics, Heidelberg)Composite Dark Matter and Neutrino Masses from a Light Hidden Sector
We present a class of models in which dark matter is composed of the composite states of a strongly coupled hidden sector. The hidden sector interacts with the standard model through the neutrino portal, allowing the relic abundance of dark matter to be set by annihilation into final states containing neutrinos. The coupling to the hidden sector also leads to the generation of neutrino masses through the inverse seesaw mechanism, with composite hidden sector states playing the role of the singlet neutrinos. We focus on the scenario in which the hidden sector is conformal in the ultraviolet, and the compositeness scale lies at or below the weak scale. We construct a holographic realization of this framework based on the Randall-Sundrum setup and study the phenomenology.On-line meeting.
2021-12-09 (Thursday)
join us at 12:15
Michał Iglicki (IFT UW)A thermal approach to t-channel singularities in cosmology
A t-channel singularity of a scattering process can occur when a stable mediator is kinematically allowed to be on-shell. Then, the cross section appears to be infinite which, obviously, cannot be a physical result. Since the mediator has no width, it is impossible to regularize the singularity using the Breit-Wigner approach. In this talk, I will discuss the conditions that are necessary for the singularity to occur. I will briefly summarize attempts to regularize the singularity that are already present in literature, especially in the case of collider physics. After showing that none of previously proposed ways to solve the problem is satisfactory in the cosmological case of a thermal medium of particles, I will present a natural solution developed within the Keldysch-Schwinger formalism. A non-zero imaginary part of the mediator's self-energy appears as a consequence of interactions between the mediator and the thermal medium. Consequently, the mediator acquires a non-zero effective decay width and the cross section becomes finite.
slides: https://mycloud.fuw.edu.pl/index.php/s/ZCarLbB3HiZHwj7
2021-12-02 (Thursday)
join us at 12:15
Anna Socha (IFT UW)A brief history of the Higgs-boson-induced reheating
According to the standard model of cosmology, the Universe at its very beginning underwent a phase of a rapid, exponential expansion, followed by a reheating period. During this epoch, the energy density, initially accumulated in oscillations of the inflaton field, was injected into the visible sector, eventually setting the initial conditions for the hot big bang. In this talk, I will discuss the production of the Standard Model (SM) radiation and dark matter adopting a generic post-inflationary scenario with a non-standard expansion history. In particular, I will explore the Higgs boson-induced reheating, assuming that it is achieved through a universal inflaton-Higgs coupling $\phi |\mathcal{H}|^2$. In presence of such interaction, the Higgs doublet acquires a $\phi$-dependent mass which generates a vacuum expectation value due to the inflaton oscillations and breaks the SM gauge symmetry. The non-zero mass of the Higgs field leads to a time-dependent inflaton decay rate during the reheating period in both standard and modified cosmologies. This, in turn, has non-trivial consequences for the dynamics of the reheating period, affecting the evolution of the radiation energy density and thus the UV freeze-in dark matter production.
slides: https://mycloud.fuw.edu.pl/index.php/s/RsX9Lozq6ZCTstR
2021-11-25 (Thursday)
join us at 12:15
Andrzej Hryczuk (NCBJ)Freeze-in of Dark Matter: recent developments
In this talk I will discuss the freeze-in dark matter paradigm focusing on various recent new ideas and observations regarding this production mechanism. In particular, after broader pedagogical introduction, I will present a novel scenario based on the freeze-in through semi-production, i.e. the inverse semi-annihilation processes. Its peculiar feature is that the production rate is suppressed by a small initial abundance of dark matter and consequently creating the observed relic density requires much larger coupling values than for the usual freeze-in. Even up to a point of leading to prospects for indirect detection searches, a rather surprising property given how difficult it is to detect dark matter in the typical freeze-in paradigm.
slides: https://mycloud.fuw.edu.pl/index.php/s/rWqf2GsEfZc76do
2021-11-18 (Thursday)
join us at 12:15
Apostolos Pilaftsis (Manchester University)Are We Already Living on a Supermanifold?
For more than half of a century, covariant and differential geometric methods have been playing a central role in the development of Quantum Field Theory (QFT). After a brief historic overview of the major scientific achievements using these methods, I will focus on the covariant and differential geometric formalism originally proposed by Vilkovisky and DeWitt (VDW). I will discuss recent developments made in addressing the uniqueness of the path-integral measure of the VDW effective action, and so address the problem of quantum frame dependence in cosmologically relevant scalar-tensor theories beyond the classical approximation. I will then turn my attention to a long-standing problem concerning the obstacles that the VDW formalism is facing from its original conception in describing generic QFTs that include fermions. I will show how in addition to bosons the VDW effective action can be extended to supermanifolds to include fermions. The so-extended formulation appears to be very promising for a complete geometrisation of realistic theories of micro-cosmos, such as the Standard Model and its gravitational sector.
slides: https://mycloud.fuw.edu.pl/index.php/s/GDgdxGDkcLn73dk