The Path to Neutrino Mass

Transcription

1 The Path to Neutrino Mass University of Aarhus 3 6 September 2007 s and s Alessandro Melchiorri, University of Rome, La Sapienza New Constraints on the Dark Side I will present new constraints on two main dark components namely dark energy and neutrinos. In particular I will discuss the importance of the theoretical assumptions on the derivation of current constraints on the dark energy equation of state and new possible techniques from the Integrated Sachs Wolfe effect to the so-called Sandage-Loeb test. I will then show new constraints on the cosmological background of relativistic particles and its impact on current determination of the age of the universe. Alessandro Mirizzi, Max Planck Institut für Physik, München Recent advances in Supernova neutrino oscillations Twenty years after SN 1987A, the vast international programme of experimental neutrino physics and astronomy guarantees that large detectors will observe a high-statistics neutrino signal from a galactic SN. In this context, I will talk about possible signatures in the observable neutrino signal, associated to neutrino flavor oscillations in supernovae. In particular, I will discuss about the surprising new effects on SN neutrino oscillations, associated to the neutrino self-interactions near a supernova core. Amand Fässler, Institute of Theoretical Physics, University of Tuebingen "The Neutrino Mass, the Double Beta Decay and Nuclear Structure In the Standard Model (SM) the neutrinoless Double Beta Decay is forbidden, but it is allowed in most Grand Unified Theories (GuT s). To allow for the neutrinoless double beta decay the neutrino must be a massive Majorana particle (identical with its antiparticle). Presently there is only one claim that the neutrinoless double beta decay has been measured in 76 Ge. But this claim is very controversial and must be verified in a second experiment. Accepted generally are today only upper limits for the neutrinoless double beta decay transition probability. But even with upper limits one can extract physics beyond the Standard Model from the

2 neutrinoless double beta decay, if one is able to calculate the nuclear matrix elements reliably. For this one needs reliable wave functions. The best studied example is the double beta decay of 76 Ge through 76 As to the final state of 76 Se. The usual procedure is now to assume that the light neutrino exchange with left-handed hadronic and left-handed leptonic currents is the dominating contribution. This allows to extract the Majorana neutrino mass. To test the reliability of the double beta decay transition matrix elements for the light neutrino exchange we calculate these matrix elements for three different sizes of basis sets, for three different forces (Bonn, Nijmegen and Argonne) and for the vacuum value for the axial coupling constant g A = 1.25 and for the quenched value g A = We also investigate different treatments of the short range correlations which are important for the neutrinoless double beta decay. With the claim of Klapdor for the neutrinoless double beta decay in 76 Ge with a half life T(1/2; 0νββ; hep-ph/ ) = ( ) years (exp. and theor. errors included): < m(ν) >= [eV] no short range correlations < m(ν) >= [eV] Jastrow correlations < m(ν) >= [eV] hypernetted chain correlations < m(ν) >= [eV] unitary correlator operator method < m(ν) >= [eV] Brückner correlations * I would like to thank my collaborators Dr. Vadim Rodin and Dr. Fedor Simkovic. Parts of the results were also obtained in collaboration with Petr Vogel and Sergey Kovalenko. Anatoly Smolnikov, Joint Institute for Nuclear Research, Moscow Status of the GERDA experiment aimed to search for neutrinoless double beta decay of Ge-76 The progress in development of the new international GERDA (GErmanium Detector Array) experiment is presented. Main purpose of the experiment is to search for neutrinoless double beta decays (0νββ) of 76 Ge. The 0νββ decay is one of the most sensitive probes of still unknown neutrino properties such as neutrino type and their mass scale. GERDA will operate with bare germanium semiconductor detectors (enriched in 76Ge) situated in liquid argon (LAr), which serves as cryogenic coolant as well as high purity shielding against external background. The experimental set up is under construction in the underground laboratory of LNGS (Italy). In Phase I of the experiment, it is planned to operate with about 18 kg of enriched germanium detectors which have been used earlier in the IGEX and Heidelberg-Moscow (HdM) experiments. About 20 kg of new 76 Ge crystals will be produced for Phase II. There is only one

3 claim of an evidence for the 0νββ decay in the Heidelberg-Moscow 76 Ge experiment by a part of the HdM collaboration. The GERDA experiment aims to check this claim within one year with 15 kg y of statistics in the Phase I at the background level of about 10 2 events/(kg kev y) and to go to higher sensitivity with 100 kg y of statistics in the Phase II at the background level of 10 3 events/(kg kev y). To reach the background level required for the Phase II new methods are required to suppress the intrinsic background of the detectors which mostly due to cosmogenically produced isotopes. The segmentation of the detectors will help to identify multiple Compton scattering events in the region of interest. In addition the novel concept to use the LAr scintillation light as anti-coincidence signal for further background suppression is under development. André Rubbia, Institute for Particle Physics, ETH, Zürich Next generation very large underground neutrino experiments: what are the options for Europe? (General Physics Colloquium, Department of Physics and Astronomy) Key questions in particle and astroparticle physics can be answered only by construction of new giant underground observatories to search for rare events and to study sources of terrestrial and extra-terrestrial neutrinos. A very active international scientific community is currently discussing these scientific topics. Europe is today leading deep underground science with its four long running and two emerging deep underground laboratories. I will discuss options and current initiatives towards a new European infrastructure capable of hosting such large detectors, addressing synergies and complementariness with the DUSEL (Deep Underground Science and Engineering Laboratory) initiative in the USA and the Japanese plans for a large upgrade at the Kamioka site. Christian Weinheimer, Institut für Kernphysik, Universität Münster Direct neutrino mass search - towards the Karlsruhe Tritium Neutrino experiment KATRIN The recent evidences for neutrino oscillation from atmospheric, solar, reactor and accelerator neutrinos show, that neutrinos of different flavor mix and that they have non-zero masses. Unfortunately, oscillation experiments can determine only differences between squared neutrino masses, but not the masses directly. This yet unknown neutrino mass scale is very important for particle physics as well as for cosmology and astrophysics. The direct neutrino mass experiments determine the neutrino mass in a model-independent way by a very precise investigation of the endpoint region of the tritium or rhenium beta decay. The KArlsruher TRItium Neutrino experiment KATRIN will search for the neutrino mass with one order of magnitude higher sensitivity of 0.2 ev/c2. This will allow to distinguish between hierarchical and quasi-degenerate neutrino mass scenarios as well as to investigate the whole cosmological relevant neutrino mass range.

4 The main components of KATRIN, the windowless gaseous molecular tritium source und the 23m long main spectrometer, are under construction. Recently, the main spectrometer has been installed at Forschungszentrum Karlsruhe and reached its extreme vacuum specifications. The status of the setup and the discussion of KATRIN`s systematics and sensitivity will be presented. Gennaro Miele, Università di Napoli "Federico II", Napoli Cosmological Neutrinos and Big Bang Nucleosynthesis: PArthENoPE code I describe the program PArthENoPE which is a high precision code for computing the abundances of light elements produced during Big Bang Nucleosynthesis and which is now publicly available. Starting from nuclear statistical equilibrium conditions the program solves the set of coupled ordinary differential equations, follows the departure from chemical equilibrium of nuclear species, and determines their asymptotic abundances as function of several input cosmological parameters as the baryon density, the number of effective neutrino, the value of cosmological constant and the neutrino chemical potential. In this framework, the cross check of BBN predictions versus LSS and CMB ones and their comparison with the experimental observations strongly bound the cosmological neutrino distribution. Gianpiero Mangano, National Institute of Nuclear Physics, Naples Beta decaying nuclei as a tool to measure relic neutrinos I will discuss the possibility to use beta decaying nuclei such as tritium to detect the low energy relic neutrino background. Jan Hamann, Technische Universität München Observational bounds on the cosmic radiation density Weakly interacting light particles, such as e.g., sterile neutrinos or axions, that may be difficult to detect in laboratory experiments, will nonetheless affect the formation of the large scale structure of the Universe due to their gravitational interaction. Their presence is generically parameterised in terms of the effective number of light particle species, N eff, whose "standard" value is ~3. However, some recent studies in the literature find that certain combinations of CMB+LSS data prefer a significantly higher value. We attempt to track down the source of these discrepancies, paying special attention to the correct treatment of systematic effects, such as galaxy-dependent bias. Our results show that the current data do not exhibit any evidence for deviations from the expectation of the cosmological standard model. José Valle, IFIC, University of Valencia

5 Neutrinos as astro-cosmo-messengers After a general overview of neutrino particle physics I discuss their role as messengers in astroparticle physics as well as some possible cosmological connections of neutrinos. Julien Lesgourgues, Laboratoire d'annecy-le-vieux de Physique Théorique, France Prospects for detecting the neutrino mass with CMB and large scale structure observations I will present a summary of the neutrino mass effect on the matter power spectrum, and of possibilities to detect this signature using future galaxy surveys and cosmic shear surveys, as well as their correlation with CMB experiments. Laurence Perotto, Laboratoire de l'accélérateur linéaire, Orsay Probing the neutrino masses with CMB gravitationnal lensing: Constraints from PLANCK and beyond I will focus on the weak lensing of the Cosmic Microwave Background (CMB) by intervening matter along the line-of-sight. I will show that CMB lensing offers an alternative and advantageous method to reconstruct the large scale structure in a range of scale where the cosmological signature of the neutrino mass is well-detectable. That's why, CMB lensing appears as a very suitable probe of the total neutrino mass. Recently, a first 3.4sigma detection of CMB lensing has been reported in the WMAP data. This result is promising for the Planck satellite, which will be launched in less than a year. Planck capabilities make the first exploitable measurement of the CMB lensing effect within its reach. After having described a general method to reconstruct the gravitational potential directly from the CMB maps, I will apply it to the Planck case for finally forecasting the Planck sensitivity to the neutrino masses. I will show that the lensing extraction makes the Planck satellite a self-sufficient experiment to yield a constraint on the sum of the neutrino masses as tight as 0.3 ev ( at 95% of C.L.). Moreover, even better constraints are accessible to the next generation of CMB experiment, more sensitive to the CMB polarisation. Finally I will briefly draw up the most annoying instrumental and astrophysical systematics which could complicate the lensing extraction and thus degrade the previous prediction of the constraints on the neutrino masses. Lily Schrempp, Deutsches Elektron-Synchrotron, Hamburg Neutrino Dark Energy Revisiting the Stability Issue The Mass Varying Neutrino Scenario provides a microscopic realization of dark energy by introducing a new non-standard Model force between neutrinos, which causes their masses to vary. We have reconsidered the issue of stability arising from the possible strong growth of density perturbations in the framework of linear perturbation theory. Our results are illustrated by meaningful examples both for stable and unstable models.

6 Manfred Lindner, Max-Planck-Institut fuer Kernphysik, Heidelberg Different interpretations of precision neutrino data Marco Cirelli, SPhT-CEA/Saclay and INFN Standard and non-standard neutrino cosmology Cosmology is currently one of the most powerful probes of the properties of neutrinos (and of possible new light particles), thanks to the fact that neutrinos play an important role in the evolution of the cosmological perturbations that we are observing today with high precision. How massive are neutrinos? How many neutrinos there are? Are they cosmologically freely streaming or they can be "sticky"? Are there new light particles? I present our results on global fits of cosmological data from the Cosmic Microwave Background, Large Scale Structure and Supernovae, that can answer some of these questions and may raise a few interesting points. Massimiliano Lattanzi, University of Oxford Decaying Warm Dark Matter and Neutrino Masses Neutrino masses may arise from spontaneous breaking of ungauged lepton number. Due to quantum gravity effects the associated Goldstone boson - the majoron - will pick up a mass. We determine the lifetime and mass required by cosmic microwave background observations so that the massive majoron provides the observed dark matter of the Universe. The majoron decaying dark matter (DDM) scenario fits nicely in models where neutrino masses arise "a la seesaw", and may lead to other possible cosmological implications. Ofer Lahav, Department of Physics and Astronomy, University College London Neutrino masses from LSS and the CMB We review the effect of neutrino mass on the growth of cosmic structure, the latest results from observations and the prospects for sub-ev upper limits. We also describe the next generation of large galaxy surveys, in particular the Dark Energy Survey, DUNE and WFMOS. Ole Høst, Dark Cosmology Centre, Copenhagen Neutrino masses from KATRIN and cosmology: frequentist and Bayesian analyses I compare the frequentist and Bayesian bounds on the effective electron neutrino mass which the KATRIN neutrino mass experiment is expected to obtain, using both an analytical likelihood function and Monte Carlo simulations of KATRIN. There are important differences in the case where the likelihood is peaked close to

7 the zero mass boundary. Then I combine the simulated KATRIN results with cosmological bounds in the form of present (post-wmap) and future (simulated Planck) results to investigate future sensitivity to the neutrino mass scale. The analysis highlights that consistent combination of such results may extend the accessible parameter range considerably. Pasquale Di Bari, Max Planck Institut für Physik, München Recent developments in leptogenesis I will review recent developments in leptogenesis. Starting from a scenario based on a very minimal set of assumptions, I will show how this can be generalized in different ways taking into account, for example, flavor effects, heavier right handed neutrino decays, and degenerate heavy neutrino spectrum. In particular I will focus on an intriguing possibility offered by flavor effects: Dirac phase leptogenesis. This is a particular scenario of leptogenesis where the Dirac phase is the only source of CP violation. This scenario provides an interesting direct link between CP violation in neutrino mixing and cosmology, and interesting bounds on the mixing angle theta 13 and on the absolute neutrino mass scale can be placed. In the end of the talk, I will also shortly discuss more drastic departures from the minimal scenario. Sergio Palomares-Ruiz, IPPP, Durham University Redshift-Integrated Resonance Dips in the Cosmic Neutrino Spectrum Resonant scattering of cosmic rays on the background radiation of the Universe can absorbe out the cosmic rays primaries, as for instance the case of the GZK suppression. Similarly, one expects absorption of primary neutrinos on the cosmic neutrino background when the center-ofmomentum energy reaches de Z-pole. In this talk we address the possibility of other resonant absorption of the astrophysical neutrino flux. We consider a variety of models with possible signals in two regions of energy where the extragalactic neutrino rate will dominate over the neutrino flux produced in the atmosphere, around MeV and above 100 TeV. We define a figure of merit for observable absorption and study different models of the literature which could give observable redshiftintegrated resonance dips. In particular we point out some very interesting cases which would indicate the presence of new physics linked to neutrinos. Signe Riemer-Sørensen, Dark Cosmology Centre, Copenhagen Sterile Neutrinos in the numsm Sterile, or non weakly interacting right handed neutrinos, are a natural part of a minimal extended standard model of particle physics (Asaka et al. 2005) which, if they exist, can explain the active neutrino masses, the baryon asymmetry of the Universe, and dark matter. If the mass difference between the active and sterile neutrinos is non-zero, the sterile neutrinos will take part in the neutrino oscillations, allowing for a radiative decay with

8 a mono-energetic photon emission predicted to lie in the X-ray range. This decays renders it a testable dark matter candidate, and from observations it is possible to constrain the mass-mixing angle parameter space of the sterile neutrinos and their possible production mechanisms. Werner Rodejohann, Max-Planck-Institut für Kernphysik, Heidelberg Neutrino physics with neutrinoless double beta decay We summarize the connection of neutrino physics with neutrinoless double beta decay. The neutrino physics potential of a measurement or an improved limit on the effective mass governing neutrinoless double beta decay is analyzed. The implications of the recent MiniBooNE results are also discussed. Yvonne Wong, Max-Planck-Institut für Kernphysik, München Measuring neutrino masses with weak gravitational lensing Weak gravitational lensing of distant galaxies by large-scale structure, also known as cosmic shear, is expected to become one of the most powerful cosmological probes in the future. I discuss the basic principles of this technique and how it can be used to constrain the neutrino mass to the 0.05 ev level.