2022 - SUMMER SEMESTER




Seminars are broadcast online at Zoom

10.05.2022

Huchan Lee

University of Southampton

Z mediated flavor changing neutral currents with a fourth vectorlike family


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We discuss Z mediated flavor changing neutral currents within a model where the hierarchical quark and lepton masses are explained via a fourth vectorlike family, together with a scalar sector consisting of two Higgs doublets augmented by a gauge singlet scalar field that spontaneously breaks an extra global U(1)' symmetry. The Z mediated flavor violating interactions arise from the mixings between the SM fermions and the vectorlike fermions, where the mixing is discussed in an analytic approximation and also exactly numerically. We first discuss charged lepton flavor violating (CLFV) τ → μ γ, τ → 3μ and Z → μ τ decays and find that they cannot significantly constrain the masses of charged vectorlike leptons. However, the 790 GeV mass bound arising from collider searches on vectorlike lepton doublets can set further constraints on the model parameter space. We also consider rare t → c Z decays as well as unitarity violation in the CKM mixing in order to constrain the quark sector of the model under consideration.

Slides


26.04.2022

Jan Heisig

Louvain University, CP3 and RWTH Aachen

Bound state effects on dark matter coannihilation - pushing the boundaries of minimal dark sectors


Bound-state formation effects can have a large impact on the dynamics of dark matter freeze-out in the early Universe, in particular, for colored coannihilators. We present a general formalism to include an arbitrary number of excitations of bound states in terms of an effective annihilation cross section. For a coannihilator in the fundamental representation of SU(3)c, we discuss radiative bound-state formation, decay, and electromagnetic transition rates among them. We then assess the impact of bound states within a minimal dark sector containing a Majorana dark matter candidate and a colored scalar t-channel mediator. We consider the well-known coannihilation regime as well as the regime of conversion-driven freeze-out (or coscattering), where the relic abundance is set by the freeze-out of conversion processes. We find that the latter is considerably enhanced into the multi-TeV region due to bound-state effects. This has far-reaching implications for the search strategies at the upcoming LHC runs as conversion-driven freeze-out predicts a long-lived coannihilator. We also comment on the role of bound-state effects in scenarios of non-thermalized dark matter, i.e. freeze-in or superWIMP production.

Slides      Video


05.04.2022

Zhi-Wei Wang

Lund University

Dark Phase Transition and Gravitational Wave of Strongly Coupled Hidden Sectors


We go beyond the state-of-the-art by combining first principal lattice results and effective field theory approaches as Polyakov Loop model to explore the non-perturbative dark deconfinement-confinement phase transition and the generation of gravitational-waves in a dark Yang-Mills theory. We further include fermions with different representations in the dark sector. Employing the Polyakov-Nambu-Jona-Lasinio (PNJL) model, we discover that the relevant gravitational wave signatures are highly dependent on the various representations. We also find a remarkable interplay between the deconfinement-confinement and chiral phase transitions. In both scenarios, the future Big Bang Observer experiment has a higher chance to detect the gravitational wave signals.

Slides


22.03.2022

Heejung Kim

IBS, Daejeon, CTPU and KAIST, Taejon

Manifesting the self-heating dynamics of a sub-component dark matter in astrophysical/cosmological observations


Scenarios of non-minimal dark matter (DM) contents and interactions inside a dark sector have drawn considerable attention, partially because of their abilities to resolve various phenomenological issues and provide extra power to many current/future experiments of searching for their signals in new and creative ways. In this talk, by taking a two-component DM scenario as an example, we demonstrate that multi-component DM scenarios can exhibit unique cosmological dynamics called 'self-heating'. During the self-heating epoch, a strongly self-interacting sub-component DM dynamically develops higher temperature than the SM one. We discuss the possible cosmological/astrophysical imprints from the temperature enhancement. Notably, we demonstrate that the warm DM constraints can be complementary to missing-energy/momentum experiments while providing additional information about the multi-component feature of DM. Reference: 2111.06808 (hep-ph)

Slides


08.03.2022

Juri Smirnov

Oskar Klein Centre for Cosmo Particle Physics, Stockholm University

Thermal Squeezeout of Dark Matter


I will discuss a detailed study of the confinement phase transition in a dark sector with a SU(N) gauge group and a single generation of dark heavy quark. We focus on heavy enough quarks such that their abundance freezes out before the phase transition and the phase transition is of first-order. We find that during this phase transition the quarks are trapped inside contracting pockets of the deconfined phase and are compressed enough to interact at a significant rate, giving rise to a second stage of annihilation that can dramatically change the resulting dark matter abundance. As a result, the dark matter can be heavier than the often-quoted unitarity bound of ~ 100 TeV. Finally I will show a concrete example where the link between the dark sector and the standard model is facilitated by a simple Zí model.

Slides