MPIK Division for Particle and Astroparticle Physics

PhD Student Seminar on Sterile Neutrinos

Date: 12 - 14 November 2012
Location: Seminar room GE 339
Schedule:

Monday, 12 November 2012

9:30 - 10:30		Introduction and general motivation for sterile neutrinos Lisa Michaels The motivation for introducing sterile neutrinos is certainly the discovery of neutrino oscillations and the following conclusion about active neutrino masses. There can be different neutrino mass terms requiring sterile states of Dirac and/or Majorana type that have different properties and can both lead to explanations why the active neutrino masses are so small. The seesaw mechanism is the most prominent ansatz, where the high scale of the sterile Majorana mass term suppresses the masses of the light, mainly active neutrinos.	Notes
10:30 - 11:30		Overview over experimental anomalies Alexander Kartavtzev The phenomenon of neutrino oscillations has been established by a number of experiments. An incomplete list includes Homestake, Gallex, Sage, Kamiokande, IMB, Soudan2, Macro, SNO and recently also Double Chooze, Reno and Daya Bay. Assuming existence of three neutrinos, one can extract neutrino mixing angles and mass differences from the data and use them to predict outcome of any other oscillation experiment. However, there is a handful of experiments, whose results are incompatible with this standard picture and hint towards an existence of an additional, sterile, neutrino. Among these are LSND, KARMEN, MiniBooNE, MINOS and many of the short-baseline reactor experiments. In this talk I will review the experimental setups and results, as well as their implications for the neutrino physics.	Notes
11:30 - 12:30		General issues of non-unitarity and tenstions between observations Juri Smirnov In the recent years several experiments reported to see anomalies which could be possibly explained by the existence of one or several sterile neutrinos. However, different anomalies favor different scenarios of additional sterile neutrinos. We will give an overview over the different scenarios and the tensions among them. Furthermore, we will discuss the issues of non unitarity of the PMNS matrix which appears in experiments at scales below the mass scale of the introduced sterile neutrino.	Notes
12:30 - 13:30		Lunch break
13:30 - 14:30		Double See-Saw Pascal Humbert The double-seesaw mechanism constitutes a natural generalization of the ideas behind the seesaw mechanism. Considering more than one additional mass scale, it provides more tolerance in satisfying constraints coming from neutrino data than the common seesaw mechanism. In my talk, I will present the standard theoretical framework of the double-seesaw mechanism together with its predictions. Following, I will discuss more general approaches and variants. Concluding, I will give a brief prospect of experiments that might distinguish between seesaw and double-seesaw mechanism.
14:30 - 15:30		Sterile neutrinos at Ice Cube Marco Salathe The IceCube Neutrino Observatory is the successor of AMANDA and currently the biggest neutrino detector. Being sensitive to all neutrino flavors above an energy of 100GeV, it was established that the IceCube detector can put constraints on the existence of a fourth sterile neutrino. The existence of such a neutrino affects significantly the fluxes of atmospheric neutrinos in the TeV range which can be tested efficiently by the IceCube detector.

Tuesday, 13 November 2012

11:30 - 12:30		Cosmological constraints on light sterile neutrinos Tibor Frossard Precision data from cosmology allow us to test the light sterile neutrino hypothesis and restrict its parameter space. We will review the main constraints coming from Big Bang Nucleosynthesis, CMB anisotropies and Large Scale Structures. We will see that current cosmological observations suggest the existence of one light sterile neutrino with mass below the eV-range.
12:30 - 13:30		Lunch break
13:30 - 14:30		Sterile neutrinos and Dark matter Michael Duerr A large number of astrophysical and cosmological observations suggests that about 20% of the total energy density of the Universe consist of some form of weakly interacting, non-baryonic matter. Putting emphasis on the possibility of keV-scale sterile neutrinos as warm dark matter candidates, we will give an introduction to particle dark matter and discuss different production mechanisms as well as observational constraints. A warm dark matter component may influence the structure formation in the Universe. We will provide an overview of recent simulation runs, partly also including baryonic matter, and discuss some of the open problems.	Notes
14:30 - 15:30		Sterile neutrinos and the 130 GeV gamma signal Daniel Schmidt A smoking gun signal for Dark Matter (DM) could be a gamma ray line observed in indirect DM searches. There is the claim that such a line is present in the Fermi LAT data near an energy of 130 GeV. I will review the "tentative" 130 GeV gamma ray line and thereby give arguments favoring DM annihilations as its origin. In particular, I will present a model in which sterile neutrinos fit the claim of the 130 GeV gamma signal.	Notes
15:30 - 16:30		nuMSM Kher Sham Lim I will discuss a simple BSM model, namely the nuMSM, that can explain the neutrino masses, baryon asymmetry of the universe (BAU) and provide a warm dark matter candidate. In nuMSM, the SM particle content is extended with 3 right-handed sterile neutrinos. The production mechanism of the lightest sterile neutrino, which is a warm dark matter candidate, will be discussed. I will then talk about the mechanism to produce the observed BAU via leptogenesis with 2 heaviest sterile neutrinos. The constraints on the masses of sterile neutrinos and certain parameters will be discussed.
16:30 - 17:30		Reactor fluxes and anitneutrino anomaly Sebastian Lindemann Updated reactor antineutrino reference spectra seem to reveal a missing electron antineutrino signal in several short baseline detectors. We will review the production mechanism of neutrinos in fission reactors and understand the methods to derive reference neutrino spectra. Using the example of the Double Chooz experiment we will discuss the most common experimental method to detect reactor electron antineutrinos via the inverse beta decay. We will compare experimental results of several short baseline experiments with their predictions and find a possible explanation of the so-called reactor antineutrino anomaly through the existence of a fourth non-standard neutrino.	Notes

Wednesday, 14 November 2012

9:30 - 10:30		Source Experiments Werner Maneschg	Notes
10:30 - 11:30		Direct detection of sterile neutrinos & collider experiments Dominik Scala There are experimental upper limits on the mixing elements between the standard model leptons and additional heavy sterile neutrinos coming from electro-weak precision measurements and - in the case of electrons - neutrinoless double beta decay. But also collider experiments provide bounds on the mixing angles and, in addition, on the heavy neutrino masses. In my talk I will present the main search modes and review the bounds found by different experiments, namely DELPHI and L3 @ LEP and - most recently - CMS @ LHC.
11:30 - 12:30		Theoretical implications of light sterile neutrinos Julian Heeck Light sterile neutrinos (eV-keV), as a possible explanation for various experiments or dark matter, pose the question of the origin of their low mass scale. A number of models have been proposed to explain the smallness of the sterile neutrino masses, making use of extra dimensions, flavor symmetries or seesaw-extensions. This talk will cover some of these models and discuss their implications.
12:30 - 13:30		Lunch break
13:30 - 14:30		Light sterile neutrinos: neutrinoless double beta decay and flavour symmetries James Barry The existence of light active neutrino masses requires new physics beyond the Standard Model, with current theoretical prejudice favouring the introduction of heavy right-handed (sterile) neutrinos: the seesaw mechanism. However, there are a number of recent experimental hints that point towards the existence of light sterile neutrinos in the eV and/or keV mass range. We examine the feasibility of incorporating sterile neutrinos of different mass scales in neutrino mass models with flavour symmetries, and study the resulting phenomenological consequences, paying particular attention to any deviations from mixing patterns as well as the predictions for neutrinoless double beta decay.
14:30 - 15:30		Sterile neutrinos from GUTs Martin Holthausen Grand Unified Theories (GUTs) are well-motivated approaches to beyond the Standard Model physics. In traditional unification where all SM particles(+3 r.h. heavy neutrinos) are unified into one 16-dimensional representation of SO(10) one would not expect light sterile neutrinos. In this talk we give a brief introduction to GUTs and discuss possibilities to obtain light sterile neutrinos in the context of GUTs.	Notes