Theorie Palaver

Programm für das Sommersemester 2021

Tuesdays, 14:30 Uhr s.t.

Institut für Physik
MITP seminar room
live at Zoom

13.04.21Raffaele Tito D'Agnolo, IPhT Saclay
I will discuss settings where the Higgs mass squared affects the vacuum expectation value of local operators and can thus act as a “trigger” of new cosmological dynamics. This triggering mechanism underlies several existing solutions to the hierarchy problem that trace the origin of the weak scale to the early history of the Universe. Thinking about these solutions more systematically from the point of view of weak scale triggers allows to understand their common predictions, to find new solutions and to identify unexpected physics related to naturalness in a rather model-independent way. As an example I discuss a BSM trigger in a Two Higgs Doublet Model and show how it can be used to link the tuning of the Higgs mass to that of the cosmological constant. This weak scale trigger demands the existence of new Higgs states necessarily comparable to or lighter than the weak scale, with no wiggle room to decouple them.
14:30 Uhr s.t., MITP seminar room, at Zoom

20.04.21Xiaofeng Xu, Bern University
Canonical Feynman integrals are of great interest in the study of scattering amplitudes at the multi-loop level. We propose to construct d log-form integrals of the hypergeometric type, treat them as a representation of Feynman integrals, and project them into master integrals using intersection theory. This provides a constructive way to build canonical master integrals whose differential equations can be solved easily. We use our method to investigate both the maximally cut integrals and the uncut ones at one and two loops, and demonstrate its applicability in problems with multiple scales.
14:30 Uhr s.t., MITP seminar room, at Zoom

04.05.21Admir Greljo, Bern U.
Recent R(K) update from the LHCb experiment at CERN reinforced the tension of B-meson decays into muons. Shortly after, the Muon g-2 experiment at Fermilab strengthened the tension in the muon anomalous magnetic moment. Immense theoretical and experimental work is still needed to possibly establish the existence of new physics, nonetheless, we can already ask relevant questions. Can muon anomalies be coherently addressed in models beyond the SM, and if so, where else should we look for confirmation? I will discuss minimal extensions of the SM based on 2103.13991.
14:30 Uhr s.t., at Zoom

11.05.21Lorenzo Ubaldi, SISSA, Trieste
A scalar inflaton coupled to a dark photon can produce a large density of the latter. I will discuss the mechanism underlying this production, which takes place mostly at the end of inflation. After reheating, the dark photons are relativistic at first and then redshift to non relativistic. Their energy density today can match that of the observed dark matter in a wide region of parameters of the model. It is interesting to study in detail also the dark photon power spectrum and its cosmic evolution, which predicts a clumpy nature of this dark matter candidate, possibly useful for experimental searches.
14:30 Uhr s.t., at Zoom

18.05.21Florian Goertz, Max-Planck-Institut für Kernphysik, Heidelberg
In this talk, we present a minimal viable scenario that unifies the gauge symmetries of the SM and their breaking sector. Our Gauge-Higgs Grand Unification setup employs 5D warped space with a SU(6) bulk gauge field that includes both a SU(5) grand unified theory (GUT) and a Higgs sector as a scalar component of the 5D vector field, solving the hierarchy problem. By appropriately breaking the gauge symmetry on the boundaries of the extra dimension the issue of light exotic new states, appearing generically in such models, is eliminated and the SM fermion spectrum is naturally reproduced. The Higgs potential is computed at one-loop, finding straightforward solutions with a realistic mh = 125 GeV. The problem of proton decay is addressed by showing that baryon number is a hidden symmetry of the model. The presence of a scalar leptoquark and a scalar singlet is highlighted, which might play a role in solving further problems of the SM, allowing for example for electroweak baryogenesis. Finally, the X and Y gauge bosons from SU(5) GUTs are found at collider accessible masses, opening a window to the unification structure at low energies.
14:30 Uhr s.t., MITP seminar room, at Zoom

08.06.21Ben Safdi, Berkeley
The quantum chromodynamics axion and axion-like particles are some of the most sought-after beyond the Standard Model particles at present because of their possible connections with the strong-CP problem, dark matter, and ultraviolet physics such as Grand Unification and String Theory. Laboratory searches are underway around the world to search for these hypothetical particles, but certain regions of axion parameter space -- such as ultralight axions with weak couplings to matter -- are notoriously difficult to probe with terrestrial experiments, despite their theoretical motivations. However, axions in this part of the parameter space may be produced in abundance within compact stars such as white dwarfs and neutron stars. It has long been recognized that axion production in compact stars opens up a new pathway for them to cool. I will point out, however, that axions may also lead to novel X-ray signatures around these stars, whereby the axions are produced within the stellar cores and then convert to photons in the strong magnetic fields surrounding the stars. I will discuss recent data taken by the XMM-Newton and Chandra telescopes from nearby neutron stars and white dwarfs that provide some of the strongest probes to-date of axions by searching for these processes.
17:30 Uhr s.t., MITP seminar room, at Zoom

15.06.21Matthew Reece, Harvard U.
This talk will take the form of two mini-talks, which are loosely related in that both involve axion (or ALP) fields. First, I will discuss challenges when fitting the muon g-2 anomaly with axion-like fields in an EFT setting. I will argue that new particles are required near the weak scale to UV complete these models, and these are subject to experimental constraints and can also affect the muon g-2 directly. This is based on arXiv:2104.03267 with Manuel Buen-Abad, JiJi Fan, and Chen Sun. Second, I will discuss how axions interacting with abelian gauge fields acquire a potential through a nonperturbative, semiclassical effect involving loops of monopoles and dyons. This is an application of the Witten effect. This is based on arXiv:2105.09950 with JiJi Fan, Katie Fraser, and John Stout.
14:30 Uhr s.t., at Zoom

22.06.21Keri Vos, Maastricht U. and Nikhef
The determination of the CKM element Vcb from inclusive semileptonic b → c semileptonic decays has reached a high precision thanks to a combination of theoretical and experimental efforts. Moreover, the long standing Vcb puzzle, a discrepancy between inclusive and exclusive determinations seems to be disappearing. In this talk, I will discuss the story of Vcb and how to continue towards even higher precision focussing on the inclusive determination. Specifically, I discuss two new strategies to improve the precision. The first is based on reparametrization invariances, which allows including higher power-suppressed terms in the heavy-quark expansion (HQE), the second is a method to control background effects using the HQE.
14:30 Uhr s.t., at Zoom

29.06.21Martin Winkler, Texas U. and Stockholm U.
I will introduce Chain inflation as an alternative to slow roll inflation in which the universe undergoes a series of transitions between different vacua. The role of the inflaton can be played by an axion which tunnels from minimum to minimum in a quasiperiodic potential. I will determine the scalar power spectrum of chain inflation and show that it is fully consistent with a ΛCDM cosmology. Then I will turn to the Hubble tension, the apparent discrepancy between local measurements of the Hubble constant H0=74 km/s/Mpc and H0=67 km/s/Mpc inferred from the CMB. I will propose Chain Early Dark Energy - the low-energy analog of chain inflation - as a solution of the H0-tension and point to a connection to today's dark energy.
14:30 Uhr s.t., MITP seminar room, at Zoom

30.06.21Gilly Elor, University of Washington
I will introduce a class of new mechanisms for low-scale baryogenesis and dark matter production that utilize the CP violation within Standard Model meson systems. Mesogenesis mechanisms operate at MeV scales and such, remarkably, are experimentally testable. I will first give an overview of B-Mesogenesis; in which baryogenesis proceeds through the oscillation and subsequent decay into a dark sector of neutral B mesons. B-Mesogenesis is testable at current hadron colliders and B-factors, and I will present results of recent studies that pave the way towards constraining (or discovering) this mechanism. Finally, I will present a recent proposal for D-Mesogenesis which relies on the CP violation of charged D mesons.
14:30 Uhr s.t., Hörsaal 20 (Geb. 1 231, J.-J.-Becher Weg 14), at Zoom

06.07.21Tevong You, CERN
We describe a new phenomenon in quantum cosmology: self-organised localisation. When the fundamental parameters of a theory are functions of a scalar field subject to large fluctuations during inflation, quantum phase transitions can act as dynamical attractors. As a result, the theory parameters are probabilistically localised around the critical value and the Universe finds itself at the edge of a phase transition. We illustrate how self-organised localisation could account for the observed near-criticality of the Higgs self-coupling, the naturalness of the Higgs mass, or the smallness of the cosmological constant.
14:30 Uhr s.t., 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