# HEP Theory Seminars SS 15

### Mon 09.03.2015, 16.00 h

S. Westhoff (Pittsburgh)

Leptophilic New Physics: Dark Matter and the Muon g-2

**Abstract:**

New heavy particles that couple only to leptons may explain the observed discrepancy in the muon anomalous magnetic moment, g-2. I discuss how the LHC can probe such new particles in direct production. Leptophilic particles are also promising candidates of dark matter, since they evade constraints from scattering off nuclei. I show that LEP constraints from loop-induced four-lepton interactions are comparable or superior to mono-photon searches. At a future electron-positron collider, lepton interactions can reveal details about the scale and structure of dark sectors.

### Thu 16.04.2015, 17.00 Uhr

A. Bharucha (TU München/Marseille)

Looking for new physics via b to s transitions: exclusive channels and form factors

### Thu 23.04.2015, 17.00 Uhr

J. Harz (UC London)

Precise Prediction of the Dark Matter Relic Density within the MSSM

### Thu 30.04.2015, 17.00 Uhr

S. Sapeta (CERN)

Calculating the dominant part of NNLO for high-pT observables

### Thu 07.05.2015, 17.00 Uhr

O. Rucharsky (EPFL Lausanne)

Decaying dark matter in X-rays?

**Abstract:**

Recently an unidentified line-like feature in the X-ray spectra of galaxies and galaxy clusters have been reported by two independent groups. I discuss the signal, consistency of its interpretation in terms of decaying dark matter and further steps that are required to confirm or rule out its dark matter origin.

### Thu 21.05.2015, 17.00 Uhr

S. Plätzer (Durham)

Improving Parton Showers

**Abstract:**

Monte Carlo event generators are indispensable tools for high energy physics theory and experiment, and parton showers form the central ingredient to these simulations. While most of recent research has went into combining parton showers and higher order corrections, parton shower development itself is becoming of increasing importance. After a short introduction to event generators in general, I will focus on recent parton shower development in the context of the Herwig++ event generator, notably concerning subleading colour effects.

### Thu 11.06.2015, 17.00 Uhr

D. Stöckinger (Dresden)

The muon g-2 and electroweak precision observables: New results in SUSY models

**Abstract:**

Low-energy observables are important complementary tests of the Standard Model and constraints of new physics. In the talk we focus on two different kinds of such observables. First we discuss the Higgs and W-boson masses in an interesting and appealing alternative SUSY model: a SUSY model with continuous R-symmetry, which behaves differently from the usual MSSM. Second we give an extensive discussion of the muon g-2, including an overview of the experimental and the SM status, and generic possibilities of new physics. New results include an surprising scenario within the MSSM which can explain the current discrepancy with TeV-scale SUSY masses, and two-loop precision corrections.

### Thu 18.06.2015, 17.00 Uhr

M. Archidiacono (Aarhus)

Neutrinos in cosmology and the case for sterile neutrinos

### Thu 25.06.2015, 17.00 Uhr

P. Serpico (LAPTH Annecy)

Revisiting cosmological applications of electromagnetic cascade theory

**Abstract:**

After a recap of the standard e.m. cascade theory, I will discuss a loophole that can have a large effect in the early universe, notably in altering primordial nucleosynthesis bounds on electromagnetically decaying relic particles. I will finally show how this may greatly simplify the possibility to address the long-standing "lithium problem" in terms of new physics models.

### Thu 02.07.2015, 17.00 Uhr

R. Schabinger (Mainz)

A Novel Approach To Integration By Parts Reduction

**Abstract:**

Integration by parts reduction is a standard component of most modern multi-loop calculations in quantum field theory. We present a novel strategy constructed to overcome the limitations of currently available reduction programs based on Laporta's algorithm. The key idea is to construct algebraic identities from numerical samples obtained from reductions over finite fields. We expect the method to be highly amenable to parallelization, show a low memory footprint during the reduction step, and allow for significantly better run-times.

### Thu 09.07.2015, 17.00 Uhr

A. Cuoco (RWTH)

Indirect Dark Matter searches searches with gamma rays and Fermi-LAT

**Abstract:**

I will review the current status of indirect Dark Matter searches in gamma rays with the Fermi Large Area Telescope (LAT), in particular in Dwarf spheroidal galaxies and in the Galactic Center. I will then focus on some alternative promising strategy using gamma-ray anisotropies.

### Thu 09.07.2015, 17.00 Uhr

M. Worek (RWTH)

Kilogram as a relic in physics: In search of a universal definition of the unit of mass

**Abstract:**

Since 1889, the international prototype of the kilogram has served to define the unit of mass in what is now known as the International System of Units (SI). This definition, which continues to serve mass metrology well, is an anachronism for twenty-first century physics. Indeed, as of 2014 the kilogram is the only SI unit that is still directly

defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Therefore, the kilogram will no doubt be redefined in the future in terms of a physical constant like the Planck constant. In this presentation I

will give a brief historical perspective on the developments that led to the current definition of the kilogram. In the next step, I will present an overview of current mass measurement procedures. And finally, I will conclude with an outlook into the future possible redefinition of the unit of mass based on fundamental principles.

### Thu 16.07.2015, 17.00 Uhr

T. Dennen (NBI Kopenhagen)

Ultraviolet Properties of Perturbative Supergravity

**Abstract:**

Over the past few years, new calculation techniques have allowed us to probe the ultraviolet behaviour of certain supergravity theories to high loop order, providing explicit checks of expectations based on traditional supersymmetry and duality symmetry analyses. In this talk, I will summarise a number of results, highlighting particular cases that are UV finite even though seemingly valid counterterms exist, and I will argue that this is due to a qualitatively new, though still mysterious, mechanism for cancellations.