Theorie Palaver

Programm für das Wintersemester 2021/2022

Tuesdays, 14:00 Uhr s.t.

Institut für Physik

Lorentz room (Staudingerweg 7, 5th floor)
live at Zoom
19.10.21Matthias Neubert, JGU Mainz
Jet cross sections at high-energy colliders exhibit intricate patterns of logarithmically enhanced higher-order corrections. In particular, so-called non-global logarithms emerge from soft radiation emitted off energetic partons inside jets. While this is a single-logarithmic effect at lepton colliders, at hadron colliders phase factors in the amplitudes lead to double-logarithmic corrections starting at four-loop order. This effect was discovered a long time ago, but not much is known about the higher-order behavior of these terms and their process dependence. We derive, for the first time, the all-order structure of these "super-leading logarithms" for generic \(2\to l\) scattering processes at hadron colliders and resum them in closed form.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

20.10.21Frank Saueressig, Nijmegen
The asymptotic safety program strives for a high-energy completion of gravity and gravity-matter systems by an interacting renormalization group fixed point, the Reuter fixed point. The fixed point renders the theory safe from unphysical divergences at high energies and equips the construction with predictive power. In this talk I will give a pedagogical introduction to the program. In particular, I will argue that the inclusion of form factors - generalizing the running couplings encountered in quantum field theory to curved spacetime - is essential for investigating questions related to the causality and unitarity of Asymptotic Safety. Moreover, I will outline how form factors provide a concrete perspective for formulating various quantum gravity programs in a unifying language.
15:00 Uhr s.t., Staudingerweg 7, 05-427

26.10.21Peera Simakachorn, DESY and U. Hamburg
In presence of a kination era, induced by a fast-moving scalar field dominating the energy density of the universe, stochastic gravitational-wave (GW) backgrounds can be dramatically enhanced. Not only this could boost the detectability of primordial GW from cosmic strings or primordial inflation at current and future-planned GW observatories, but it could also help constraining particle theories that generate the kination phase. We find that kination era at the GeV-EeV scale can induce a GW peak in the window of ET and CE. In this work, we present two classes of spinning axion models in which a phase of matter-domination followed by kination-domination is naturally generated. Ultimately, it is possible to relate the GW signatures to the relic abundance of axion dark matter or to the baryon asymmetry of the universe.
14:30 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

02.11.21Miguel Escudero, TUM
We are living exciting times in Cosmology and we may be at the edge of a shift in the cosmological paradigm. At present, there is a 4-5 sigma tension in the value of the Hubble constant between the value that is inferred locally (from Cepheids and type Ia Supernovae) and the value predicted in LCDM. This tension has been growing for the past 6-7 years and many models have been proposed to account for it. In the first part of this seminar, I will review the status of the Hubble tension. I will discuss the observational situation and review the main theoretical approaches developed to account for it. In the second part of the talk, I will focus on my contribution to the topic (see 1909.04044, 2004.01470, 2103.03249). I will show that the Hubble tension can be substantially ameliorated in the presence of an eV-scale pseudo-Goldstone boson that interacts with neutrinos: the Majoron. This particle is directly related to the neutrino mass mechanism and naturally arises in the context of the type-I seesaw mechanism with a spontaneously broken global U(1)L symmetry. Remarkably, I will further show that in some regions of the parameter space, this scenario could also account for the observed baryon asymmetry of the Universe via sterile neutrino oscillations in the early Universe. Thus, providing an intriguing link between low-scale leptogenesis, neutrino mass generation and the Hubble tension.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

09.11.21Joan Ruiz, IFIC, Valencia U. - CSIC
Recent experimental results on the B-anomalies, CP-violation in charm, or the muon (g-2) hint at new physics models where the additional interactions are specific to the quark and lepton families. In this context, searches for the electric dipole moment (EDM) of heavy-flavored baryons are especially motivated. Using bent crystal technology and the highly energetic beams of the LHC, the EDM of very short-lived particles can be measured for the first time (1612.06769, 2010.11902, 2110.00845). In addition, the direct determination of the tau (g-2) is possible with this novel experimental method (1901.04003). The different aspects of the measurement will be summarized along with the expected sensitivities. From a more phenomenological perspective, we will also see what are the effective operators contributing to the baryon EDM and what is their expected size. In particular, new limits on the charm and bottom quark EDM are derived from already existing measurements (1905.02513). We will analyze the implications of these bounds for new physics models, comparing them against other competing observables.
14:30 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

10.11.21Kevin Falls, SISSA
In this talk I will present a novel scheme for the exact renormalisation group motivated by the desire of reducing the complexity of practical computations. The key idea is to specify renormalisation conditions for all inessential couplings, leaving us with the task of computing only the flow of the essential ones. To achieve this, a renormalisation group equation for the effective average action which incorporates general non-linear field reparameterisations is utilised. The field reparameterisations allow one to fix the values of inessential couplings. The scheme has been used to investigate the Wilson-Fisher fixed point in the three dimensional Ising model and the Reuter fixed point in quantum gravity. I will discuss the results of these investigations and the implications for quantum gravity.
15:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

16.11.21Jeff Dror, UC, Santa Cruz
Existing searches for cosmic axions relics have relied heavily on the axion being non-relativistic and making up dark matter. However, light axions can be copiously produced in the early Universe and remain relativistic today, thereby constituting a Cosmic axion Background (CaB). In this talk I will study the production and detection of a CaB. Prototypical examples of axion sources are thermal production, dark-matter decay, parametric resonance, and topological defect decay. Each of these has a characteristic frequency spectrum that can be searched for in axion direct detection experiments. I will focus on the axion-photon coupling and study the sensitivity of current and future versions of ADMX, HAYSTAC, DMRadio, and ABRACADABRA to a CaB, finding that the data collected in search of dark matter can be repurposed to detect axion energy densities well below limits set by measurements of the energy budget of the Universe. In this way, direct detection of relativistic relics offers a powerful new opportunity to learn about the early Universe and, potentially, discover the axion.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

23.11.21Guilherme Guedes, U. Granada and LIP
In this talk, I will discuss the calculation of the renormalization group equations (RGEs) of theories extending the Standard Model effective field theory (SMEFT) with higher-dimensional operators or with a new degree of freedom. In the first case, I will explore the running of bosonic dimension-eight operators triggered by two dimension-six interactions. In the second scenario I will consider extending the SMEFT to include an axion-like particle and study the RGE effects up to dimension 5. In both cases, some phenomenological consequences will be discussed.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

30.11.21Abhishek Banerjee, Weizmann Institute of Science
The relaxion mechanism, which was proposed recently, can address the hierarchy problem without resorting to new physics at the TeV scale. Our prior efforts on this subject have produced several new results, which have interesting phenomenological implications. We have shown that the relaxion can account for the observed dark matter relic density and can be probed in various different frontiers. The relaxion has scalar coupling to the SM and as a result of the oscillating DM background, the fundamental constants of natures are oscillating in time as well. In this talk, I will discuss how the relaxion could be a viable DM candidate and then will discuss how to search for scalar DM (relaxion) using precision spectroscopy.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

07.12.21Eran Palti, Ben-Gurion University of the Negev
In this talk, I will introduce a particular formulation of the Weak Gravity Conjecture in AdS space in terms of the self-binding energy of a particle. The holographic CFT dual of this formulation corresponds to a certain convex-like structure for operators charged under continuous global symmetries. Motivated by this, we propose a conjecture that this convexity is a general property of all CFTs, not just those with weakly-curved gravitational duals. It is possible to test this in simple CFTs, the conjecture passes all the tests performed so far.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

zukünftige Termine
18.01.22Anne Mareike Galda, JGU Mainz
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

Slides can be found in each seminar's page under 'Attachments'.

Video recordings for the SoSe 2021 can be found on Panopto:

Video recordings for the WiSe 2020/21 can be found on Panopto:

Koordination: Kontakt:

Dr. Enrico Morgante

Dr. Javier Fuentes-Martin