Theorie Palaver

Programm für das Wintersemester 2020/2021

Tuesdays, 14:30 Uhr s.t.

Institut für Physik
MITP seminar room
live at Zoom

10.11.20Javier Fuentes-Martin, JGU Mainz
In this talk, I will present a model for third-family quark-lepton unification at the TeV scale featuring a composite Higgs sector. The model is based on a variant of the Pati-Salam model, the so-called 4321 model. The spontaneous symmetry breaking to the SM gauge group is triggered dynamically by a QCD-like confining sector. The same strong dynamics also produces a pseudo Nambu-Goldstone boson Higgs, connecting the energy scales of both sectors. The model predicts a massive U1 vector leptoquark coupled dominantly to the third generation, recently put forward as a possible solution to the B-meson anomalies.
14:30 Uhr s.t., at Zoom

17.11.20Ana Peñuelas, JGU Mainz
We perform a general model-independent analysis of \(b \to c \tau \bar{\nu}_\tau\) transitions, including measurements of \(\mathcal{R}_D\), \(\mathcal{R}_{D^*}\), their \(q^2\) differential distributions, the longitudinal \(D^*\) polarization \(F_L^{D^*}\), and constraints from the \(B_c \to \tau \bar{\nu}_\tau\) lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented working with a minimal set of assumptions: new physics is present only in the third generation of leptons, there are not light right-handed neutrinos, the electroweak symmetry breaking is linearly realized and the CP-conserving limit is taken. The solutions of the fit are interpreted in terms of hypothetical new-physics mediators. The impact of \(F_L^{D^*}\), measured by Belle last year is studied in detail. The difficulty to accommodate this measurement motivates the relaxation of some of our assumptions so the impact of a non-linear electroweak symmetry breaking and the addition of light right-handed neutrinos is studied. From the obtained results we predict selected \(b \to c\tau\bar\nu_\tau\) observables, such as the baryonic transition \(\Lambda_b \to \Lambda_c \tau \bar{\nu}_\tau\), the forward-backward asymmetries \(\mathcal{A}_\text{FB}^{D^{(*)}}\), the \(\tau\) polarization asymmetries \(\mathcal{P}_\tau^{D^{(*)}}\), the longitudinal \(D^*\) polarization fraction \(F_L^{D^*}\) and several additional differential observables.
14:30 Uhr s.t., at Zoom

24.11.20Davide Racco, Perimeter Institute
The low frequency part of the gravitational wave spectrum generated by local physics, such as a phase transition, is largely fixed by causality, offering a clean window into the early Universe. Due to the difference between sub-horizon and super-horizon physics, it is inevitable that there will be a distinct spectral feature that could allow for the direct measurement of the conformal Hubble rate at which the phase transition occurred. As an example, free-streaming particles present during the phase transition affect the production of super-horizon modes. This leads to a steeper decrease in the spectrum at low frequencies as compared to the well-known causal \(k^3\) super-horizon scaling of stochastic gravity waves. If a sizeable fraction of the energy density is in free-streaming particles, they even lead to the appearance of oscillatory features in the spectrum. If the universe was not radiation dominated when the waves were generated, a similar feature also occurs at the transition between sub-horizon to super-horizon causality. These features can be used to show surprising consequences, such as the fact that a period of matter domination following the production of gravity waves actually increases their power spectrum at low frequencies.
14:30 Uhr s.t., at Zoom

01.12.20Saereh Najjari, JGU Mainz
I will introduce a scenario where both the Higgs and a complex scalar dark matter candidate arise as the pNGB of breaking a global \(SO(7)\) symmetry to \(SO(6)\). In our construction the symmetry partners of the Standard Model top-quark are charged under a hidden \(SU(3)_c\) color group. We show how the Large Hadron Collider along with current and next generation dark matter experiments will explore this framework.
14:30 Uhr s.t., at Zoom

08.12.20Aldo Cotrone, Florence U. and INFN
I will first review the basics of holography and some properties of the Sakai-Sugimoto model, the top-down holographic theory closest to QCD. Then, in this model I will describe the process of nucleation of bubbles of true vacua in the case of two first-order transitions: the confinement/deconfinement and chiral symmetry breaking/restoration ones. Finally, using these information, I will present the calculation of the gravitational wave spectra generated in these transitions, when the Sakai-Sugimoto model is employed as a dark sector. Prospects of detection will be discussed.
14:30 Uhr s.t., MITP seminar room, at Zoom

11.12.20Alexandros Papageorgiou, University of Minnesota
Motivated by some of the recent swampland conjectures, we study a model of dark energy in which a quintessence axion slowly rolls in a steep potential due to its interactions with a U(1) or an SU(2) gauge field. We compare the differences between the U(1) and SU(2) cases and specify the parameter space for which the model is compatible with observations. We also apply our methodology to studying the transition between a pre-inflationary era and inflation and note some interesting oscillatory effects in the particle production parameter which could lead to interesting phenomenology. Finally we analyze the potential of the "Warm Dark Energy" model to produce gravitational waves observable by PTA, CMB polarization or spectral distortion experiments and find a negative result.
15:30 Uhr s.t., MITP seminar room, at Zoom

19.01.21Danny van Dyk, TUM, Munich
I will discuss theory predictions for exclusive b->s ll decays within the SM and beyond, with emphasis on the hadronic matrix elements. There are two categories of these matrix elements: local form factors, and nonlocal contributions arising from e.g. four-quark operators. I will report the status and report recent progress from QCD-based methods on the non-local hadronic matrix elements arising from intermediate charm states. A particular focus will be a recent derivation of a dispersive bound on the non-local matrix element as discussed in arXiv:2011.09813.
14:30 Uhr s.t., at Zoom

zukünftige Termine
26.01.21Zhengkang (Kevin) Zhang, Caltech
Matching a UV theory onto a low-energy EFT can be efficiently accomplished with functional methods. The functional approach is conceptually appealing: all calculations are performed within the UV theory at the matching scale, and no prior determination of an EFT operator basis is required. In this talk, I will present a simple prescription for functional matching up to one loop order, which accommodates any relativistic UV theory that contains generic interactions among scalar, fermion and vector fields. I will also introduce STrEAM (SuperTrace Evaluation Automated for Matching), a Mathematica package that helps streamline the procedure.
17:30 Uhr s.t., MITP seminar room, at Zoom

02.02.21Anders Eller Thomsen, University of Bern
14:30 Uhr s.t., at Zoom

09.02.21Riccardo Barbieri, SNS Pisa
Motivated by the hierarchy problem and by the pattern of quark masses and mixings, I describe a picture of flavour physics that should give rise in a not too distant future to observable deviations from the SM in Higgs compositeness and/or in B-decays (if LFV confirmed) or perhaps even in supersymmetry, depending on the specific realization.
14:30 Uhr s.t., MITP seminar room, at Zoom

16.02.21Nick Evans, Southampton U.
14:30 Uhr s.t., MITP seminar room, at Zoom

Koordination: Kontakt:

Dr. Enrico Morgante

Dr. Javier Fuentes-Martin