HEP Theory Seminars WS 17/18
Thu 12.10.2017, 16.30 h
M. Winkler (Nordita)
A Precision Search for WIMPs with Charged Cosmic Rays
Thu 19.10.2017, 16.30 h
J. Brod (Dortmund)
EDM constraints on flavor-diagonal CP violation
The discovery of the Higgs boson opened a new window to the search for new physics related to electroweak symmetry breaking. For instance, sizeable CP-violating contributions to the top Yukawa coupling can be essential for electroweak baryogenesis.
Low-energy precision observables like electric dipole moments (EDM) put stringent bounds on this coupling. However, in order to take into possible cancellations into account, the contributions of all Yukawa couplings have to be calculated. After a short review on EDMs as probes of new physics, I will explain the calculation of the different contributions and show preliminary results.
Thu 26.10.2017, 16.30 h
E. Bellini (Oxford)
Maximal freedom at minimum cost: efficient description of general scalar-tensor theories in cosmology
In this talk I will introduce the main motivations to explore theories of gravity alternative to General Relativity. In particular, I will focus on the popular class of scalar-tensor theories, discussing their formulation and how to parametrize them efficiently on a cosmological background. This framework is optimal to describe large class of models at once, which makes it ideal for the implementation into Einstein-Boltzmann solvers as CLASS. I will discuss some of the features of hi_class and present the main results. Finally, I will mention why the recent detection of two neutron stars merger improved heavily the constraints on alternative theories of gravity.
Thu 02.11.2017, 16.30 h
J. Henn (Mainz)
Regge limit from an anomalous dimension
We consider a model of massive scattering amplitudes in N = 4 super Yang-Mills, which is analogous to light-by-light scattering. Working at the planar level, we provide the full three-loop amplitudes. We then derive various asymptotic expansions in physically interesting regimes. We find a surprisingly simple structure in the Regge limit, and suggest a simple form of the first power-suppressed terms. We propose that the latter are controlled by an anomalous dimension, and provide perturbative evidence for this conjecture.
Thu 09.11.2017, 16.30 h
S. Ando (Amsterdam)
Power of angular power: Implications for dark matter and cosmic neutrinos
Particle nature of dark matter is yet to be revealed. A promising class of candidates is the weakly interacting massive particles, which may give signatures of high-energy gamma rays through self-annihilation or decay. Independently of this, the origin of the high-energy neutrinos detected with IceCube is still to be uncovered. I will give an overview of the anisotropy analyses of both high-energy gamma rays and neutrinos that provide unique probes of evidence of dark matter annihilation and neutrino sources. The angular power spectrum, cross correlation with catalogs of galaxies and lensing data has been applied to the gamma-ray background to constrain contributions from dark matter annihilation and decay as well as astrophysical sources. The same idea can be applied to the current and future data of high-energy neutrinos, to get interesting insights of source contributions and properties.
Thu 16.11.2017, 16.30 h
R. Durrer (Genf)
Testing General Relativity with the Large Scale Structure of the Universe
In the measured angular and redshift distribution of galaxies we see not only the density fluctuations of the matter distribution but also effects from peculiar velocities, from lensing and other relativistic effects. I shall discuss how these enter the observations of the galaxy distribution and how they may be extracted and how they can help us to test Einstein’s equations in cosmology.
Thu 23.11.2017, 16.30 h
J. Lindert (Durham)
Efficient algorithms for one-loop amplitudes - OpenLoops
Thu 30.11.2017, 16.30 h
M. Spannowski (Durham)
The Higgsploding Universe
Higgsplosion is a dynamical mechanism that introduces an exponential suppression of quantum fluctuations beyond the Higgsplosion energy scale and further guarantees perturbative unitarity in multi-Higgs production processes. I will review the calculations that indicate a factorial growth of the h* → n h transition amplitude and will outline how such a growth leads to an exponential suppression of large particle virtualities. If realised in nature, Higgsplosion has astonishing consequences for the consistency of the Standard Model. I will discuss these consequences and will present phenomenological implications that could potentially lead to observation of Higgsplosion in future experiments.
Thu 07.12.2017, 16.30 h
F. Iocco (Sao Paulo)
The dark matter distribution in the Milky Way (its uncertainties and effects on determination of new physics)
I will present the latest determinations of the dark matter distribution in the Milky Way. After a review of the methods and involved observations, I will concentrate on how observational uncertainties -some of which unlikely to be reducible in the close future- affect the current determinations, with consequences ranging from cosmology to particle physics.
Thu 14.12.2017, 16.30 h
A. Hoang (Wien)
On the Top Quark Mass
The currently most precise measurements of the top quark mass are obtained from kinematic reconstruction obtained at hadron colliders. The observables designed to make these measurements cannot be calculated using analytic methods in QCD and therefore reply on multipurpose Monte-Carlo event generators. As a consequence,
the interpretation of the measured top quark masses is theoretically difficult. In my talk I explain the theoretical issues inherent to this problem. It is currently also not yet fully understood, up to a conceptual upper bound, how large the uncertainty is when one interprets the result as measurements of the pole mass. I then explain one
approach to shed some light on the interpretation problem using the concept of MC calibration with top mass sensitive observables which can be computed systematically at hadron level using analytic methods. As these observables can currently only be calculated for boosted top quarks, the problem of how the current most precise top quark mass measurements have to be interpreted is strictly speaking still open.
Thu 25.01.2018, 16.30 h
A. Boyarsky (Leiden university)
Sterile neutrino Dark Matter : the current status
I will review the basics for DM candidate, current X-ray bounds and the status of 3,5 kev line (with some new results), Ly-alpha forest and cosmological constraints and a few words about particles physics searches from sterile neutrinos.
Thu 01.02.2018, 16.30 h
M. Lüscher (CERN)
The Yang-Mills gradient flow in QCD -- theory and applications
The Yang-Mills gradient flow is a relatively new tool in QCD, which allows the theory to be probed in interesting ways. Non-perturbative renormalization in lattice QCD is currently the most important field of application, but the flow is theoretically inspiring and has other uses as well. In this talk, an introduction to the subject is provided and some illustrative applications are discussed.