"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2023-08-24 (Thursday)
room B0.14, Pasteura 5 at 12:00 
Antonio Jr. Iovino (U. Rome La Sapienza)Primordial black holes: From dark matter to GWs experiments
Primordial Black Holes (PBHs) have recently attracted ample attention as they may explain some of the LIGO/Virgo/KAGRA observations and significantly contribute to the dark matter in our universe. The standard formation scenario assumes PBHs form out of the collapse of large radiation over-densities in the early universe. In this context, we present a new prescription to compute the abundance of PBHs mass fraction in the presence of local non-gaussianity (NG). Simultaneously, recent releases of data from multiple pulsar timing array (PTA) experiments reveal compelling evidence of Hellings-Downs angular correlations. This discovery implies that the observed stochastic common spectrum could be interpreted as a stochastic gravitational wave background. We study whether the signal may originate from gravitational waves induced by high-amplitude primordial curvature perturbations. Such large perturbations may be accompanied by the generation of a sizeable PBH abundance. We discuss in which scenarios the inclusion of non-Gaussianities in the computation of the abundance can lead to a signal compatible with the PTA experiments without overproducing PBHs.
2023-07-27 (Thursday)
room B0.14, Pasteura 5 at 12:15
Lekhika Malhotra (IIT Bombay)Cogenesis of visible and dark sector asymmetry in a minimal seesaw framework
Recently there is a renewed interest in exploring the Dark sector of the universe in a more constrained way. Particularly in reference (Imprint of the seesaw mechanism on feebly interacting dark matter and the baryon asymmetry), the FIMP ( Feebly Interacting Massive Particle) scenario was shown to be realized with a minimal extension of the SM with three sterile neutrinos in the spirit of νMSM. In this paper, we show that without invoking any additional symmetries of the model, we can realize the idea of ADM (Asymmetric Dark Matter) signaling a common origin of the matter-anti-matter asymmetries in visible as well as Dark sectors. The model allows for a range of dark matter masses, ∼ 1 − 100keV, with correct active neutrino masses through the Type-I seesaw mechanism. Thus, the model explains the neutrino masses, Dark Matter abundance and replicates matter-anti-matter asymmetry of the visible sector in the Dark sector, all in a version of the νMSM. The asymmetry in the dark sector is manifested in the predominance of one parity of the heavy neutrinos in the comoving frame, which should be determinable in the ongoing experiments.
room B0.14, Pasteura 5 at 13:15
Zafri Ahmed Borboruah (Indian Inst. Tech. Mumbai)Left-Right Symmetry Breaking and Gravitational Waves : A Tale of Two Phase Transitions
We study possible ways gravitational waves (GW) are sourced in a theory with minimal left-right symmetry breaking. Generically first order phase transitions (FOPT) lead to gravitational waves sourced by bubble collisions, while second order phase transitions (SOPT) do not. Interesting variants on the standard classification of phase transitions occur due to the breaking of discrete parity combined with the limitation of light cone in the early Universe. If local effective potential signals SOPT or a cross over, breaking of discrete parity in conjunction with the finiteness of the causal horizon leads to a causal horizon limited second order phase transition, which results in domain walls (DWs) separating left-like and right-like domains. Thus the putative SOPT also gives rise to GW via decaying domain walls, testable at experiments such as IPTA, DECIGO, and LISA. On the other hand, for the case of FOPT, we get the usual signal from spontaneously created bubbles, but also a late forming domain wall structure separating the two types of vacua. Thus the traditional FOPT case gives rise to two distinct peaks in the spectrum of GW, verifiable for the low symmetry breaking scales 10^4−10^6 GeV, but beyond the reach of currently planned experiments for a high scale ∼ 10^10 GeV. Finally, we point out that a version of the left-right symmetric model which separates parity breaking from gauge symmetry breaking is also subject to domain wall formation and amenable to GW observations.
2023-06-30 (Friday)
room 1.01, Pasteura 5 at 12:15
Disrael Camargo Neves da Cunha (Louvain University, Belgium)Stochastic gravitational waves from long cosmic strings
I will report the findings of 2205.04349. We compute the expected strain power spectrum and energy density parameter of the stochastic gravitational wave background created by a network of long cosmic strings evolving throughout cosmic history. The contribution of cosmic string loops is discarded, and our result provides a robust lower bound of the expected signal that applies to most cosmic string models.
2023-06-15 (Thursday)
room 1.01, Pasteura 5 at 12:15
Daniel Schmitt (Frankfurt Uni.)Gravitational waves from QCD-triggered conformal symmetry breaking
Classically conformal Standard Model extensions predict an intriguing thermal history of the early universe. In contrast to the common paradigm, the onset of the electroweak phase transition can be significantly delayed while the universe undergoes a period of thermal inflation. Then, a first-order QCD chiral phase transition could not only trigger electroweak symmetry breaking but also initiate the exit from supercooling. I will outline how such a scenario arises naturally in a large class of scale-invariant Standard Model extensions. Then, I will discuss how to study the transition dynamics by means of effective QCD models. Finally, the gravitational wave signal from the chiral phase transition in a supercooled universe is presented. While a large amount of latent heat is naturally involved if thermal inflation ends, a supercooling period prior to the QCD scale considerably enhances the timescale of the transition. This enhancement implies great observational prospects at future observatories.
2023-05-18 (Thursday)
room 1.01, Pasteura 5 at 12:15
Maxim Laletin (IFT UW)The impact of non-equilibrium effects on the relic density of dark matter
The standard method of dark-matter (DM) relic-density calculation (which is widely used for the freeze-out mechanism of DM production, but is not limited to it) is based on solving the Boltzmann equation for the number density and relies on the assumption that DM particles are in thermal equilibrium with the SM plasma or a secluded thermal equilibrium in the dark sector is maintained. The interplay of different interactions in some DM models can lead to a deviation of the DM energy distribution from the equilibrium shape before the relic abundance is established and this deviation can have a considerable impact on the predicted amount of DM in the Universe.In my talk I am going to outline more elaborate approaches to calculating the distribution function of DM particles (and the corresponding DM number density) and consider the application of these methods to a scenario in which the DM self-interaction has a significant impact on the relic density.
2023-05-11 (Thursday)
room 1.01, Pasteura 5 at 12:15
Chihiro Sasaki (IFT UWr)Parity doubling in QCD matter
In this talk, we focus on spontaneous breaking and restoration of chiral symmetry in hot and/or dense QCD matter, and discuss how in-medium modifications of hadrons due to the QCD phase transition would emerge in experimental and observational signals. The following (selected) topics will be presented: signatures in dilepton production in heavy-ion collisions via chiral mixing and the equation of state in the inner cores of massive neutron stars
2023-04-27 (Thursday)
room 1.01, Pasteura 5 at 12:15
Michał Łukawski (IFT UW)Dark matter in supersymmetric Twin Higgs models
Supersymmetric Twin Higgs models allow for naturally lowelectroweak scale without much fine-tuning. Often, the lightest supersymmetric particleresides in the twin sector, and could be a candidate for dark matter. I will consider the twin stau and twin bino as candidates for dark matter in these class of models. All experimental constraints, including self-interaction bounds, are satisfied for wide range of the parameters. However, future direct detection experiments such as LUX-ZEPELIN will probe most of the natural parameter space.
2023-04-20 (Thursday)
room 1.01, Pasteura 5 at 12:15
Jacek Osiński (CAMK)An Overview of Dark Matter Production in Nonstandard Cosmologies with a focus on Axions
The Universe is typically assumed to be radiation-dominated in the period preceding big bang nucleosynthesis, however we do not currently have any observational probes confirming this. Nonstandard cosmological histories, where some other form of energy density dominates for a time, commonly arise in theories of the early Universe. These histories have important consequences for processes, such as dark matter production, occurring in that time. In this talk I will briefly review nonstandard cosmological histories and their effects on dark matter production focusing on axion dark matter.
2023-04-13 (Thursday)
room 1.01, Pasteura 5 at 12:15
Mateusz Zych (IFT UW)Hydrodynamical constraints on bubble wall velocity
Terminal velocity reached by bubble walls in first order phase transitions is an important parameter determining both primordial gravitational-wave spectrum and production of baryon asymmetry in models of electroweak baryogenesis. We developed a numerical code to study the real-time evolution of expanding bubbles and investigate how their walls reach stationary states. Our results agree with profiles obtained within the so-called bag model with very good accuracy, however, not all such solutions are stable and realised in dynamical systems. Depending on the exact shape of the potential there is always a range of wall velocities where no steady state solutions exist. This behaviour in deflagrations was explained by hydrodynamical obstruction where solutions that would heat the plasma outside the wall above the critical temperature and cause local symmetry restoration are forbidden. For even more affected hybrid solutions causes are less straight forward, however, we provide a simple numerical fit allowing one to verify if a solution with a given velocity is allowed simply by computing the ratio of the nucleation temperature to the critical one for the potential in question.