Theoretical Particle Physics

Speakers: Gevorg Karyan (AANL, Yerevan, Armenia)

Monte Carlo simulations in High Energy Physics play a crucial role in providing final physics results beyond the limitations of detector acceptance and resolution effects. These simulations serve as a bridge between theoretical models and experimental observations, enabling precise modeling of particle interactions, background estimation, and detector response. However, to ensure accurate and reliable outcomes, it is essential to tune the Monte Carlo generators using real data. Tuning aligns simulation parameters with experimental measurements, reducing systematic uncertainties and improving the fidelity of physics analyses. This presentation highlights the importance of Monte Carlo tuning in modern HEP experiments, discusses multi-parameter tuning methodologies, and illustrates its impact through concrete examples from electron-positron collider kinematics.

https://indico.physik.uni-siegen.de/event/603/

Speakers: Alex Khodjamirian

How large is the electric dipole moment of electron  in Standard Model?

https://indico.physik.uni-siegen.de/event/569/

Speakers: Arne Schirrmacher (HU Berlin)

https://indico.physik.uni-siegen.de/event/535/

Speakers: Uli Haisch (Munich, Max Planck Inst.)

In this talk, I will use specific examples to illustrate the complementarity and interplay between low-energy CP and flavor observables and high-p_T measurements at the LHC, with a focus on the top-quark and Higgs-boson sectors. Both model-independent and model-dependent approaches will be discussed, demonstrating how flavor physics not only provides essential constraints on the Standard Model effective field theory but can also provide valuable guidance for ATLAS and CMS searches for physics beyond the Standard Model at the LHC.

https://indico.physik.uni-siegen.de/event/556/

Speakers: Eleftheria Malami

Updated measurement of CP violation and polarisation in $B_s^0\to J/\psi\bar{K}^*(892)^0$ decays

https://indico.physik.uni-siegen.de/event/570/

Speakers: Michael Drewsen (Aarhus University)

Trapped, single complex molecular ions have in the past been demonstrated to be sympathetically cooled translationally to near the Doppler laser cooling limit through the Coulomb interaction with laser cooled and co-trapped single atomic ions [1]. Furthermore, simpler molecular ions have been sympathetically cooled of to near their motional ground state through resolved sideband cooling of the atomic ions [2,3], and their internal state have been prepared either by buffer gas cooling [4] or probabilistic state detection [5-7].
In the talk, I will discuss, our efforts to extend ground state cooling of complex molecular ions with photon recoil spectroscopy in both the sideband unresolved [8] and resolved regime [9] with the aim – among others – of measuring the chirality of single molecules through a photon recoil spectroscopy version of the schemes presented in in Ref. [10]. Finally, to illustrate the very diverse potential of recoil spectroscopy, an example of how to test for potential extensions to quantum mechanics with charged macromolecules [11] will briefly be discussed.
 
[1] K. Højbjerre et al., Phys. Rev. A 77, 030702(R) (2008).[2] G. Poulsen, PhD thesis, Aarhus University, 2011.[3] R. Rugango et al., New J. Phys. 17, 035009 (2015).[4] K. Hansen et al., Nature 508, 76 (2014).[5] Wolf, F. et al., Nature 530, 457 (2016).[6] C.-W. Chou et al., Nature 545, 203 (2017).[7] M. Sinhal et al., Science 367, 1213 (2020).[8] E. H. Clausen et al., Phys. Rev. A 105, 063709 (2022).[9] P. O.Schmidt et al., Science 309, 749 (2005).[10] N. V. Vitanov and M. Drewsen, Phys. Rev. Lett. 122, 173202 (2019).[11] E. Lenler-Eriksen, M. Drewsen and M. Carlesso, New J. Phys. 26 113008 (2024).

https://indico.physik.uni-siegen.de/event/533/

Speakers: Joachim Brod (University of Cincinnati)

Direct detection via scattering on atomic nuclei remains one of our best hopes to shed light on the mystery of dark matter. Several effective theory frameworks exist that try to capture most of the physics without committing to a specific model. I will present the ultimate effective theory for direct detection, valid for non-relativistic dark matter of any spin. I will outline the bottom-up construction of this effective theory and discuss the differences to (and advantages over) existing approaches.

https://indico.physik.uni-siegen.de/event/614/

Speakers: Ilija Milutin

Kinematic Moments of $\bar{B}\to X_cl\bar{
u}_l$ to Order $\mathcal{O}(\Lambda_{QCD}^5/m_b^5)$

https://indico.physik.uni-siegen.de/event/571/

Speakers: Giancarlo Soavi (Institute of Solid State Physics, Friedrich Schiller University Jena)

Layered materials, such as graphene and transition metal dichalcogenides (TMDs), possess unique nonlinear optical (NLO) properties [1], which allow a full control over the intensity [2,3], polarization [4] and orbital angular momentum [5] of the light emitted via perturbative harmonic generation processes. Furthermore, TMDs have emerged as the ideal platform to study the interplay between space-inversion and time-reversal symmetries, which can be independently engineered in by tuning the number of layers (space-inversion) and via excitation with circularly polarized light (time-reversal). In this talk, I will discuss our recently developed approaches to modulate the bandgap in TMDs using ultrafast and off-resonant excitation, and the possibility to subsequently detect broken time-reversal symmetry using second [6,7] and third harmonic generation. In particular, all-optical bandgap modulation can be achieved via the coherent optical Stark and Bloch-Siegert effects, with the additional degree of freedom to create either a symmetric or asymmetric bandgap opening in the ±K valleys, depending on the number of layers of the sample and the polarization state of the excitation beam. In monolayer TMDs, a valley asymmetric bandgap modulation effectively corresponds to breaking of time-reversal symmetry. In bilayer TMDs, broken time-reversal symmetry manifests itself as a valley symmetric bandgap modulation, which lifts the spin degeneracy. Subsequently, both symmetric and asymmetric all-optical bandgap modulation can be probed via polarization and intensity dependent measurements of perturbative nonlinear optics.
References

Dogadov, O. et al., “Parametric Nonlinear Optics with Layered Materials and Related Heterostructures”, Laser & Photon. Rev., Vol. 16, No. 9, 2100726, 2022

Soavi, G. et al., “Broadband, electrically tunable third-harmonic generation in graphene”, Nat. Nanotechnol., Vol. 13, 583-588, 2018

Ghaebi, O. et al., “Ultrafast Opto-Electronic and Thermal Tuning of Third-Harmonic Generation in a Graphene Field Effect Transistor”, Adv. Science, Vol. 11, No. 31, 2401840, 2024

Klimmer, S. et al., “All-optical polarization and amplitude modulation of second-harmonic generation in atomically thin semiconductors”, Nat. Photon., Vol. 15, 837-842, 2021

Sinelnik, A. et al., “Ultrafast all-optical second harmonic wavefront shaping”, Nat. Comms., Vol. 15, 2507, 2024

Herrmann, P. et al., “Nonlinear valley selection rules and all-optical probe of broken time-reversal symmetry in monolayer WSe2”, Nat. Photon., Vol. 19, 300-306, 2025

Herrmann, P. et al., “Nonlinear All-Optical Coherent Generation and Read-Out of Valleys in Atomically Thin Semiconductors”, Small, Vol. 19, No.37, 2301126, 2023

https://indico.physik.uni-siegen.de/event/539/