# HEP Theory Seminars WS 16/17

### Thu 20.10.2016, 16.30 h

P. Marquard (DESY Zeuthen)

The top quark and its mass

**Abstract:**

The top quark is the heaviest particle in the Standard Model and plays an important role for precision observables. I will discus recent results for the translation between different mass renormalization schemes and the possibilities to measure the mass of the top quark at a future linear collider.

### Thu 27.10.2016, 16.30 h

G. Mangano (Naples)

Big Bang Nucleosynthesis: recent updates and impact on cosmology

### Thu 03.11.2016, 16.30 h

M. Viel (Trieste)

Properties of the Universe from Intergalactic Medium data

### Thu 10.11.2016, 16.30 h

T. Weigand (Heidelberg)

Challenges in String Phenomenology

**Abstract:**

String Theory is our leading candidate for a fundamental, UV finite quantum theory of gravity and particle interactions. While in ten spacetime dimensions it is uniquely defined without any free dimensionless parameters, it seems to possess a plethora of effectively four-dimensional solutions, called the landscape of string vacua. Each solution by itself makes definite, falsifiable predictions for particle physics and cosmology. At the same time, the existence of a multitude of four-dimensional string vacua puts us before practical challenges in making concrete contact with observations. In this talk we will describe what we can and what we cannot expect of studying the solution space of string theory both from a theoretical and a model building perspective.

### Thu 17.11.2016, 16.30 h

M. Bartelmann (Heidelberg)

A new theory for cosmic structure formation

### Thu 24.11.2016, 16.30 h

A. Falkowski (Paris)

Effective Field Theory approach to SM precision tests

**Abstract:**

I will discuss the effective field theory (EFT) framework as a tool to search for physics beyond the standard model (SM). The framework involves extending the SM Lagrangian by a set of higher-dimensional operators. Possible effects of these operators are, e.g., modified couplings of the SM Higgs and gauge bosons or new contact interactions involving four SM fermions. In this talk, I will sketch the connection between the EFT parameters and observables at LEP, LHC and other colliders. Then, I will present current constraints on various higher-dimensional EFT operators and future prospects to probe them with better accuracy. Finally, I will discuss what these constraints tell us about some specific models of physics beyond the SM.

### Thu 01.12.2016, 16.30 h

E. Laenen (NIKHEF)

Resummation in QCD: what, why and how?

### Thu 08.12.2016, 16.30 h

I. Oldengott (Bielefeld)

The impact of interacting neutrinos on the CMB

**Abstract:**

The cosmic microwave background anisotropies have been providing useful insights into neutrino physics in the past decade. This naturally raises the question whether we can also test non-standard neutrino interactions using cosmological observations. After a short introduction to cosmological perturbation theory, I will present the Boltzmann hierarchy for neutrinos including interactions with a scalar particle. Such interactions appear, for example, in Majoron-like models of neutrino mass generation. I will furthermore present for the first time our preliminary results for the signal induced in the cosmic microwave background, based on the numerical implementation of the collisional neutrino Boltzmann hierarchy in the Boltzmann code CLASS.

### Thu 15.12.2016, 16.30 h

M. Scherer (Heidelberg)

Higgs Mass, Top Mass and the Scale of New Physics

**Abstract:**

In view of the measured Higgs mass of 125 GeV, the perturbative renormalization group evolution of the Standard Model suggests that our Higgs vacuum might not be stable. I will present recent work where we connected the usual perturbative approach and the functional renormalization group which allows for a straightforward inclusion of higher-dimensional operators in the presence of an ultraviolet cutoff. In the latter framework vacuum stability can be studied in the presence of higher-dimensional operators. Their presence can have a sizable influence on the maximum ultraviolet scale of the Standard Model and the existence of instabilities. Further, I explain how such operators can be generated in specific models.

### Thu 12.01.2017, 16.30 h

J. Plefka (HU Berlin)

Scattering amplitudes and hidden symmetries in supersymmetric gauge theory

**Abstract:**

After a brief introduction to the role of symmetries in physics and quantum field theory, I shall discuss supersymmetric gauge theories in 4d and their dual description in terms of string theory in 5d anti-de-Sitter space. Moreover, novel on-shell methods for the efficient construction of parton scattering amplitudes are reviewed and their hidden infinite dimensional symmetry structure will be exposed.

### Thu 19.01.2017, 16.30 h

M. Schulze (HU Berlin)

Probing the top quark electroweak couplings at the LHC

**Abstract: **

I will discuss our current knowledge of the top quark electroweak interactions and present strategies for probing them in the processes pp --> ttbar+gamma/Z/H. In addition to first-time constraints from the LHC, I will mention results from LEP and B-factories as well as prospects from future lepton (ILC) and hadron (FCC) colliders.

### Thu 26.01.2017, 16.30 h

J. Zavala (Reykjavik)

Towards an effective theory of structure formation with new dark matter physics

### Thu 02.02.2017, 16.30 h

F. Boudjema (LAPTh Annecy)

MicrOMEGAs: a code for the calculation of dark matter observables

**Abstract:**

MicrOMEGAs is a code for the calculation of the relic density, the direct detection and the indirect detection of dark matter in a variety of New Physics scenarios beyond the Standard Model. The code allows also the study the phenomenology of these models at the colliders as well as from indirect precision observables. We will describe the different physics components and modules needed to build such a tool and illustrate how a generic New Physics model can be implemented automatically. For some specific models we will describe how results beyond a tree-level annihilation cross sections can be incorporated.