253 research outputs found
Tau Lepton Physics: Theory Overview
The pure leptonic or semileptonic character of tau decays makes them a good
laboratory to test the structure of the weak currents and the universality of
their couplings to the gauge bosons. The hadronic tau decay modes constitute an
ideal tool for studying low-energy effects of the strong interactions in very
clean conditions; a well-known example is the precise determination of the QCD
coupling from tau-decay data. New physics phenomena, such as a non-zero
tau-neutrino mass or violations of (flavour / CP) conservation laws can also be
searched for with tau decays.Comment: 20 pages, latex, 5 Postscript figures, uses espcrc2.sty, Invited Talk
at the Fourth International Workshop on Tau Lepton Physics (TAU96), Colorado,
September 199
Evaluation of and
This talk summarizes the recent developments in the evaluation of the leading
order hadronic contributions to the running of the QED fine structure constant
, at , and to the anomalous magnetic moment of the
muon . The accuracy of the theoretical prediction of these
observables is limited by the uncertainties on the hadronic contributions.
Significant improvement has been achieved in a series of new analyses which is
presented historically in three steps: (I), use of spectral functions in
addition to cross sections, (II), extended use of perturbative QCD and
(III), application of QCD sum rule techniques. The most precise values obtained
are: , ,
yielding , and with which one finds for the complete
Standard Model prediction .
For the electron , the hadronic contribution is .Comment: 13 page
Volcanic Flank Collapse, Secondary Sediment Failure and Flow‐Transition:Multi‐Stage Landslide Emplacement Offshore Montserrat, Lesser Antilles
Volcanic flank collapses, especially those in island settings, have generated some of the most voluminous mass transport deposits on Earth and can trigger devastating tsunamis. Reliable tsunami hazard assessments for flank collapse‐driven tsunamis require an understanding of the complex emplacement processes involved. The seafloor sequence southeast of Montserrat (Lesser Antilles) is a key site for the study of volcanic flank collapse emplacement processes that span subaerial to submarine environments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from one of the most extensive mass transport deposits offshore Montserrat, which exemplifies multi‐phase landslide deposition from volcanic islands. The deposits reveal emplacement in multiple stages including two blocky volcanic debris avalanches, secondary seafloor failure and a late‐stage erosive density current that carved channel‐like incisions into the hummocky surface of the deposit about 15 km from the source region. The highly erosive density current potentially originated from downslope‐acceleration of fine‐grained material that was suspended in the water column earlier during the slide. Late‐stage erosive turbidity currents may be a more common process following volcanic sector collapse than has been previously recognized, exerting a potentially important control on the observed deposit morphology as well as on the runout and the overall shape of the deposit
Sector collapse kinematics and tsunami implications - SEKT, Cruise No. M154/1, April 3 - April 25, 2019, Mindelo (Cape Verde) - Point-á-Pitre (Guadeloupe)
Summary
Deep-seated collapses of volcanic islands have generated the largest volume mass flows worldwide. These mass flows might trigger mega-tsunamis. The way in which these collapse events are emplaced is poorly understood, even though this emplacement process determines the scale of associated tsunamis. Key questions such as whether they are emplaced in single or multiple events, how they may incorporate seafloor sediment to increase their volume, and how they are related to volcanic eruption cycles and migration of volcanic centers, remain to be answered. This project forms a part of the comprehensive study of large volcanic island landslide deposits and is directly linked to IODP drilling campaign in the Lesser Antilles (IODP Leg 340). Unfortunately, Leg 340 only recovered material from a single site within the volcanic landslide deposits off Montserrat, and even at this site, recovery was not continuous. This single IODP site is insufficient to document lateral variation in landslide character, which is critical for understanding how it was emplaced. The main scientific goals of this project are to determine where the landslides are sourced from; to understand how these landslides are emplaced; and to understand the relationship between landslides, eruption cycles and initiation of new volcanic centres. Combining 3D seismology (Leg 1) and MeBo cores (Leg 2) provides a unique dataset of the internal structure, composition and source of material throughout a volcanic island landslide. The results will significantly contribute to understanding the emplacement of volcanic island landslides and they will allow us to assess the associated tsunami risk
From gradual spreading to catastrophic collapse - Reconstruction of the 1888 Ritter Island volcanic sector collapse from high-resolution 3D seismic data
Volcanic island flank collapses have the potential to trigger devastating tsunamis threatening coastal communities and infrastructure. The 1888 sector collapse of Ritter Island, Papua New Guinea (in the following called Ritter) is the most voluminous volcanic island flank collapse in historic times. The associated tsunami had run-up heights of more than 20 m on the neighboring islands and reached settlements 600 km away from its source. This event provides an opportunity to advance our understanding of volcanic landslide-tsunami hazards. Here, we present a detailed reconstruction of the 1888 Ritter sector collapse based on high-resolution 2D and 3D seismic and bathymetric data covering the failed volcanic edifice and the associated mass-movement deposits. The 3D seismic data reveal that the catastrophic collapse of Ritter
occurred in two phases: (1) Ritter was first affected by deep-seated, gradual spreading over a long time period, which is manifest in pronounced compressional deformation within the volcanic edifice and the adjacent seafloor sediments. A scoria cone at the foot of Ritter acted as a buttress, influencing the displacement and deformation of the western flank of the volcano and causing shearing within the volcanic edifice. (2) During the final, catastrophic phase of the collapse, about 2.4 km³ of Ritter disintegrated almost entirely and travelled as a highly energetic mass flow, which incised the underlying sediment. The irregular topography west of Ritter is a product of both compressional deformation and erosion. A crater-like depression underlying the recent volcanic cone and eyewitness accounts suggest that an explosion may have accompanied the catastrophic collapse. Our findings demonstrate that volcanic sector collapses may transform from slow gravitational deformation to catastrophic collapse. Understanding the processes involved in such a transformation is crucial for assessing the hazard potential of other volcanoes with slowly deforming flanks such as Mt. Etna or Kilauea
Correspondences in Arakelov geometry and applications to the case of Hecke operators on modular curves
In the context of arithmetic surfaces, Bost defined a generalized Arithmetic
Chow Group
(ACG) using the Sobolev space L^2_1. We study the behavior of these groups
under pull-back and push-forward and we prove a projection formula.
We use these results to define an action of the Hecke operators on the ACG of
modular curves and to show that they are self-adjoint with respect to the
arithmetic intersection product. The decomposition of the ACG in
eigencomponents which follows allows us to define new numerical invariants,
which are refined versions of the self-intersection of the dualizing sheaf.
Using the Gross-Zagier formula and a calculation due independently to Bost and
Kuehn we compute these invariants in terms of special values of L series. On
the other hand, we obtain a proof of the fact that Hecke correspondences acting
on the Jacobian of the modular curves are self-adjoint with respect to the
N\'eron-Tate height pairing.Comment: 38 pages. Minor correction
P and T Odd Asymmetries in Lepton Flavor Violating Tau Decays
We calculated the differential cross sections of the processes in which one
of the pair created tau particles at an e^+ e^- collider decays into lepton
flavor violating final states e.g. tau -> mu gamma, tau -> 3 mu, tau -> mu ee.
Using the correlations between angular distributions of both sides of tau
decays, we can obtain information on parity and CP violations of lepton flavor
non-conserving interactions. The formulae derived here are useful in
distinguishing different models, since each model of physics beyond the
standard model predicts different angular correlations. We also calculate
angular distributions of the major background process to tau -> l gamma search,
namely tau -> l nu \bar{\nu} gamma, and discuss usefulness of the angular
correlation for background suppression.Comment: 31 pages, 5 figure
- …