"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2019-11-28 (Thursday)
room 1.01, Pasteura 5 at 12:15 
Roberto Vega-Morales (University of Granada)Dark matter fields from the end of inflation
In this talk a new production mechanism for vector dark matter (VDM) is presented in which the VDM is produced at the end of inflation. This mechanism relies on a pseudo scalar coupling between the inflaton and the vector field strength which leads to a tachyonic instability and exponential production of one transverse polarization of the vector field, reaching its maximum near the end of inflation. These transverse vectors can account for the observed dark matter relic density today in the mass range micro-eV to tens of TeV. Furthermore, since they are produced coherently with very high occupation number and with a single polarization, the nature of the VDM today is in the form of dark matter fields who's typical size is determined by the Hubble scale at the end of inflation. Some of the potential phenomenology of these objects is also discussed.
2019-11-21 (Thursday)
room 1.01, Pasteura 5 at 12:15
Marcin Badziak (IFT UW)Supersymmetric Twin Higgs models and dark matter
Twin Higgs (TH) models explain the non-discovery of new colored particles responsible for natural electroweak symmetry breaking. I will discuss supersymmetric UV completions of TH models that feature natural electroweak symmetry breaking even for stop and gluino masses above 2 TeV and show that the Lightest Supersymmetric Particle which generically resides in the twin sector is a natural dark matter candidate with promising signals at future direct-detection experiments.
2019-11-14 (Thursday)
room 1.01, Pasteura 5 at 12:15
Da Huang (IFT UW)Strong Dark Matter Self-Interaction from a Stable Scalar Mediator
In face of the small-scale structure problems in the collisionless cold dark matter (DM) paradigm, a popular solution is to introduce a strong DM self-interaction which can be generated non-perturbatively by a MeV-scale light mediator. However, if such mediator is unstable and decays into SM particles, the model is severely constrained by the DM direct and indirect detection experiments. In this talk, I will introduce a model of self-interacting fermionic DM, which is featured by a light stable scalar mediator. In the model, the DM relic abundance is dominated by the fermionic DM particle which is generated mainly via the freeze-out of its annihilations to the stable mediator. Since this channel is invisible, the DM indirect detection constraints should be greatly relaxed. Furthermore, the direct detection signals are suppressed to the unobservable level since fermionic DM scatterings with a nucleon appear at one-loop level. By further studying the bounds from the CMB and BBN on the visible channels involving the dark sector, we show that there is a large parameter space which can generate appropriate DM self-interactions at dwarf galaxy scales, while compatible with other experimental constraints.
2019-11-07 (Thursday)
room 1.01, Pasteura 5 at 12:15
Yohei Ema (DESY)Purely gravitational dark matter production
In this talk, I will discuss gravitational production of dark matter in the early universe. In particular, I will carefully evaluate the particle production rate from the transition epoch to the inflaton oscillation epoch in a realistic inflation model, and point out that the gravitational production is efficient even if dark matter mass is much larger than the Hubble scale during inflation as long as it is smaller than the inflaton mass. I will first discuss a scalar field case, and then move to a vector field case.
2019-10-31 (Thursday)
room 1.01, Pasteura 5 at 12:15
Chunshan Lin (IFT UW)A novel matter coupling in Einstein gravity
The old school knowledge tells us that the matter can couple to Einstein gravity in either minimal or Brans-Dicke manner. Recently we discovered a novel type of matter coupling in Einstein gravity. This type of matter coupling is theoretically self-consistent in the sense that all constraints in the Hamiltonian are preserved to be first class. At low energy scale it recovers the classic standard predictions of Einstein gravity + minimal coupling, including the gravitational potential, equivalence principle and so on, while at the high energy scale much richer phenomenology is granted, for instance, the theory is free from cosmological singularity. This type of matter coupling also predicts a universal lower bound on the cross section between dark matter particle and Standard Model particles. Ref: for Hamiltonian analysis, see P. A. M. Dirac, "Lectures on Quantum Mechanics" (Yeshiva University, New York 1964).
2019-10-24 (Thursday)
room 1.01, Pasteura 5 at 12:15
Andrzej Hryczuk (NCBJ)Dark Matter at the TeV frontier
The standard weak-scale WIMP paradigm seems to be losing its charm. Indeed, despite decades of experimental effort no convincing signal of such a DM particle has been found. What changes when the WIMP mass moves from O(100 GeV) to O(1-10 TeV)? In this talk I will address this question and explore new challenges as well as interesting new phenomena that emerge when going to the TeV scale and beyond. Bound state formation, Sommerfeld effect, large NLL corrections are examples of effects that start to be generically important and require careful theoretical treatment. I will also discuss detection prospects of heavy DM, with special emphasis on indirect searches.
2019-10-17 (Thursday)
room 1.01, Pasteura 5 at 12:15
Ogan Özsoy (IFT UW)Probing Early Universe on Small Scales
Observations of Cosmic Microwave Background ( CMB ) radiation appear to be consistent with the simplest realizations of inflationary paradigm: single field slow-roll inflation. In practice, CMB probes can provide us information about the inflationary dynamics only for a limited range of scales, corresponding to a small portion of the dynamics when compared with the required time span for inflation in solving the standard problems of Hot Big Bang cosmology. This situation leaves us with a large portion of the dynamics together with a vast range of scales that are pretty much uncharted and yet to be explored. In this talk, I will focus on two possible observational windows together with a simple primordial mechanism that can provide us the opportunity to probe the inflationary dynamics on scales much smaller compared to the CMB. In this context, I will show two exemplary scenarios that has potential to accomplish this goal through enhanced scalar and tensor fluctuations during inflation.
2019-10-10 (Thursday)
room 1.01, Pasteura 5 at 12:15
Dimitrios Karamitros (NCBJ)Recalculating freeze-in
The freeze-in mechanism has become very popular over the past few years. One reason for this is its ability to explain the dark matter relic abundance with suppressed couplings, and thus evading (usually) all experimental constraints. However, the production of dark matter often is not treated carefully, and so some aspects of frozen-in relics are not pointed-out. In this talk, I will try to summarize some of the ways freeze-in can be different than one expects. I will show as generally as possible the effects of thermal masses, quantum statistics, and potential non-standard cosmological expansion on freeze-in.
2019-10-03 (Thursday)
room 1.01, Pasteura 5 at 12:15
Kazuki Sakurai (IFT UW)