Theorie Palaver

Programm für das Sommersemester 2022

Tuesdays, 14:00 Uhr s.t.

Institut für Physik
Lorentz room (Staudingerweg 7, 5th floor)
live at Zoom

26.04.22Lennert Thormählen, Univ. of Heidelberg
The axion is much lighter than all other degrees of freedom introduced by the Peccei-Quinn mechanism to solve the strong CP problem. It is therefore natural to use an effective field theory (EFT) to describe its interactions. Loop processes calculated in the EFT may however explicitly depend on the ultraviolet cutoff. In general, the dimensionful couplings suggest to identify it with the Peccei- Quinn symmetry-breaking scale. An example are K+ → π+ + a decays that will soon be tested to improved precision and whose amplitude is dominated by the term logarithmically dependent on the cutoff. This talk will critically examine the adequacy of using such a naive EFT approach to study loop processes by comparing EFT calculations with ones performed in complete QCD axion models. In DFSZ models, for example, the cutoff is found to be set by additional Higgs degrees of freedom and to therefore be much closer to the electroweak scale than to the Peccei-Quinn scale. In fact, there are non-trivial requirements on axion models where the cutoff scale of loop processes is close to the Peccei-Quinn scale, such that the naive EFT result is reproduced. This suggests that the existence of a suitable UV embedding may impose restrictions on axion EFTs. We provide an explicit construction of a model with suitable fermion couplings and find promising prospects for NA62 and IAXO.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

03.05.22Rodolfo Capdevilla, U. of Toronto and Perimeter Institute
The Fermilab Muon g−2 collaboration has recently released its first measurement of (g−2)μ. This result is consistent with previous Brookhaven measurements and together they yield a statistically significant 4.2σ discrepancy with the Standard Model prediction. New physics solutions to (g−2)μ feature light weakly coupled neutral particles or heavy strongly coupled charged particles. In this talk I present an experimental program of existing and proposed experiments that can completely cover the set of theories that explain this anomaly.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

16.05.22Ennio Gozzi, Trieste
This seminar consists of a journey on the path-integral approach to classical mechanics and a short walk on “dreams in progress” regarding the possible role of the action in the dark matter and dark energy problems.
10:00 Uhr s.t., THEP seminar, at Zoom

17.05.22Jack Holguin, Ecole Polytechnique
Final states in collider experiments are characterized by correlation functions of the energy flow operator - which plays the roll of an idealised calorimeter. In this talk, I will show that the top quark imprints itself as a peak in the three-point correlator at an angle determined by its mass and transverse momentum. This provides direct access to one of the most important parameters of the Standard Model in one of the simplest field theoretical observables. The analysis I will present provides a new paradigm for a precise top mass determination that is, for the first time, highly insensitive to soft physics and underlying event contamination.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

24.05.22Stefan Stelzl, TU Munich
We consider matter density effects in theories with a false ground state. Large and dense systems, such as stars, can destabilize a metastable minimum and allow for the formation of bubbles of the true minimum. Interestingly these bubbles are not necessarily confined to the dense region, but can escape to infinity. This leads to a phase transition in the universe after the formation of stars, and therefore has significant impact on e.g. solutions to the electroweak hierarchy problem based on dynamical selection of the electroweak vacuum. We work out some of the phenomenological consequences of such density triggered late phase transitions and put new constraints on the parameter space of some benchmark relaxion models.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor)

07.06.22Andreas Crivellin, PS and U. Zürich
Hints for the violation of lepton flavour universality (satisfied within the SM) have accumulated in recent years. In particular, deviations from the SM predictions were observed in semi-leptonic B decays (b->sll and b->ctau), in the anomalous magnetic moment of the muon (g-2), in leptonic tau decays and di-electron searches. Furthermore, also the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly, can be interpreted as a sign of lepton flavour universality violation. In this talk I review the status of these anomalies and give an overview of the possible interpretations in terms of new physics models.
14:00 Uhr s.t., at Zoom

14.06.22Fernando Marchesano, Madrid, IFT
String theory has been used to construct models of particle physics and cosmology in which Quantum Gravity is automatically incorporated. Such models always present certain features, whose importance was up to now deemed secondary. But what if they were an actual imprint of Quantum Gravity into high energy physics? The Swampland Programme aims to unveil the general constraints that Quantum Gravity imposes on effective field theories of particle physics and cosmology, in order to derive actual predictions. In this talk I will consider those proposals that describe the energy scales that appear all the way up to the Planck mass, describe their implications for models of high energy physics, and discuss the current open problems that stem from them.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

15.06.22Roberto Percacci, SISSA, Trieste
A scalar theory can have many Gaussian (free) fixed points, corresponding to Lagrangians of the form ‑\phi\box^n\phi. We use the non-perturbative RG to study the flow from the free theory with four derivatives (n = 2) to the free theory with two derivatives (n = 1), in the presence of a shift-invariant interaction. We show that the anomalous dimension changes continuously in such a way that at the endpoints the fields have the correct dimensions of the respective free theories. These results generalize to other values of n, as well as to nonlinear sigma models.
10:00 Uhr s.t., Galilei room, at Zoom

21.06.22Rodolfo Ferro, JGU-Mainz
The estimation of $\alpha$ at the electroweak scale is an important parameter required for electroweak precision tests. It is computed through a combination of $\e^+e^-\rightarrow\mathrm{hadrons}$ data plus perturbative QCD contributions. The combination of data and pQCD can be optimized to reduce the error on the prediction of $\alpha(M_Z)$. Here, I will study how different groups choose the theory/data splitting and compare the type of errors associated with each framework. Later, I will discuss the relation of the running of $\alpha$ with the one of the weak mixing angle. Finally light new physics which might affect the measurement of the weak mixing angle at low energies will be discussed.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

28.06.22Manuel Reichert, University of Sussex
Over the past decades, the asymptotic safety scenario has matured into a viable contender for a consistent theory of quantum gravity. A pressing open question concerns the unitarity of the theory. I will present important steps towards tackling this issue and show the first direct computation of the graviton spectral function in asymptotically safe quantum gravity with a novel Lorentzian renormalisation group approach. The resulting graviton spectral function displays a massless one-graviton peak and a positive multi-graviton continuum with an asymptotically safe scaling for large spectral values, though being gauge-dependent. To understand the intricacies, I will contrast this to a perturbatively well-controlled computation of spectral functions in gauge theories with an infrared Banks-Zaks fixed point. I will indicate consequences for scattering amplitudes and unitarity.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

05.07.22Sravan Kumar, Tokyo Institute of Technology
Cosmic inflation is an important paradigm of the early Universe which is so far developed in two equivalent ways, either by geometrical modification of Einstein's general relativity (GR) or by introducing new forms of matter beyond the standard model of particle physics. Starobinsky's R+R^2 inflation based on a geometric modification of GR is one of the most observationally favorable models of cosmic inflation based on a geometric modification of GR. In this talk, I will discuss in detail the fundamental motivations for Starobinsky inflation and present how certain logical steps in the view of its UV completion lead to the emergence of a gravity theory that is non-local in nature. Then I will establish how one can perform studies of the early Universe in the context of non-local gravity and what are the observational consequences in the scope of future CMB and gravitational waves. I will discuss in detail how non-local R^2-like inflation can be observationally distinguishable from the local effective field theories of inflation. Finally, I will comment on prospects of non-local gravity as a promising candidate for quantum gravity.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

12.07.22Myriam Mondragon, UNAM
We present models with an extended Higgs sector, three Higgs doublets, which have an underlying S3 flavour symmetry. S3 is the smallest non-Abelian discrete group, corresponding to the permutation of three objects, which makes it naturally suitable for a flavour symmetry. We apply this symmetry "universally" to the fermionic and scalar sectors. We review some previous results in the fermionic sector (quarks and leptons), as well as recent results in the Higgs sector derived from the minimization of the potential and the explicit calculation of the Higgs-Higgs and Higgs-gauge boson couplings. We show that in the exact alignment limit (when only one of the Higgs bosons couples to the gauge bosons), the results at tree level coincide exactly with the Standard Model ones. We present the allowed parameter space for the scalar masses in the two possible alignment scenarios, with some interesting consequences. We also present the results for a dark matter candidate coming from this type of models, with a fourth inert Higgs.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor)

19.07.22Mariana Grana, Institut de Physique Théorique
One of the biggest problems in string compactifications is the large number of massless fields associated to deformations of the internal geometry. These “moduli” get masses from fluxes wrapping non-trivial cycles on the manifold. Fluxes have an associated charge, which on a compact manifold has to satisfy tadpole cancelation conditions. The tadpole conjecture proposes that the charge induced by the fluxes needed to stabilise a large number of moduli grows linearly with the number of moduli. In this talk I will go over the basics of flux compactifications, explain the conjecture, present its motivation, supporting evidence and consequences.
14:00 Uhr s.t., Lorentz room (Staudingerweg 7, 5th floor), at Zoom

09.09.22Raymond Co, Minnesota U.
We established a paradigm where the (QCD) axion’s novel cosmological evolution, a rotation in the field space, can give rise to axion dark matter via kinetic misalignment and can generate the observed baryon asymmetry of the Universe via axiogenesis. The axion rotation also leads a kination era, leaving unique signatures in the primordial gravitational wave spectrum. For ultralight (QCD) axions, this cogenesis scenario makes intriguing predictions on axion properties more experimentally accessible than the conventional ones. For heavy and cosmologically unstable QCD axions, the predictions from axiogenesis point to regions that can be probed by neutrino experiments and long-lived particle searches. We will also discuss how the presence of an axion-muon coupling will facilitate such probes at, e.g., ArgoNeuT, DUNE, FASER 2, and SHiP.
13:30 Uhr s.t., Minkowski room

09.09.22Michael Robert Trott, Niels Bohr Institute, University of Copenhagen
In recent years, the effective field theory approach to the Standard Model, the SMEFT, has been used to study LHC data with ever increasing theoretical precision and sophistication. However, the complexity of this theory lead to several barriers to substantial theoretical progress. In particular, the explosion in the number of parameters in the SMEFT as a function of operator mass dimension, and the technical challenge or reformulating SM predictions consistently into the SMEFT were very serious problems. This called into question the possible success and value of the SMEFT physics program over the long term. I will discuss how these challenges have been overcome. The key point leading to this advance, is the understanding that the projection of curved scalar field spaces generated by the Higgs onto a naive flat field space understanding-- implicitly embedded into the usual SMEFT Lagrangian, and approach -- was the root cause of many problems, technical challenges and confusions. Many outstanding issues have now been addressed and immediately overcome by reformulating the SMEFT noting its curved scalar field space(s) - in the Geometric SMEFT. Some examples of the benefits of this approach will be presented, and explained.
10:30 Uhr s.t., Minkowski room

Slides can be found on iAnnounce ( 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. Philipp Böer

Dr. Fatemeh Elahi

Dr. Enrico Morgante