22,374 research outputs found
An Model for Lepton Mass Matrices with Nearly Minimal Texture
We propose a simple extension of the electroweak standard model based on the
discrete symmetry that is capable of realizing a nearly minimal
Fritzsch-type texture for the Dirac mass matrices of both charged leptons and
neutrinos. This is achieved with the aid of additional and
symmetries, one of which can be embedded in . Five complex scalar
singlet fields are introduced in addition to the SM with right-handed
neutrinos. Although more general, the modified texture of the model retains the
successful features of the minimal texture without fine-tuning; namely, it
accommodates the masses and mixing of the leptonic sector and relates the
emergence of large leptonic mixing angles with the seesaw mechanism. For large
deviations of the minimal texture, both quasidegenerate spectrum or inverted
hierarchy are allowed for neutrino masses.Comment: 11pp, 2 figures. v2: vev alignment addressed, additional analysis
performed; to appear in PR
The Quest for an Intermediate-Scale Accidental Axion and Further ALPs
The recent detection of the cosmic microwave background polarimeter
experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically
excludes all plausible axion models where its decay constant is above
GeV. Moreover, there are strong theoretical, astrophysical, and cosmological
motivations for models involving, in addition to the axion, also axion-like
particles (ALPs), with decay constants in the intermediate scale range, between
GeV and GeV. Here, we present a general analysis of models
with an axion and further ALPs and derive bounds on the relative size of the
axion and ALP photon (and electron) coupling. We discuss what we can learn from
measurements of the axion and ALP photon couplings about the fundamental
parameters of the underlying ultraviolet completion of the theory. For the
latter we consider extensions of the Standard Model in which the axion and the
ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global
chiral (Peccei-Quinn (PQ)) symmetries, occuring accidentally as low
energy remnants from exact discrete symmetries. In such models, the axion and
the further ALP are protected from disastrous explicit symmetry breaking
effects due to Planck-scale suppressed operators. The scenarios considered
exploit heavy right handed neutrinos getting their mass via PQ symmetry
breaking and thus explain the small mass of the active neutrinos via a seesaw
relation between the electroweak and an intermediate PQ symmetry breaking
scale. We show some models that can accommodate simultaneously an axion dark
matter candidate, an ALP explaining the anomalous transparency of the universe
for -rays, and an ALP explaining the recently reported 3.55 keV gamma
line from galaxies and clusters of galaxies, if the respective decay constants
are of intermediate scale.Comment: 43pp, 4 figures. v2: version accepted for publication in JHE
Time dependent transformations in deformation quantization
We study the action of time dependent canonical and coordinate
transformations in phase space quantum mechanics. We extend the covariant
formulation of the theory by providing a formalism that is fully invariant
under both standard and time dependent coordinate transformations. This result
considerably enlarges the set of possible phase space representations of
quantum mechanics and makes it possible to construct a causal representation
for the distributional sector of Wigner quantum mechanics.Comment: 16 pages, to appear in the J. Math. Phy
Probing the Effects of Lorentz-Symmetry Violating Chern-Simons and Ricci-Cotton Terms in Higher Derivative Gravity
The combined effects of the Lorentz-symmetry violating Chern-Simons and
Ricci-Cotton actions are investigated for the Einstein-Hilbert gravity in the
second order formalism modified by higher derivative terms, and their
consequences on the spectrum of excitations are analyzed. We follow the lines
of previous works and build up an orthonormal basis of operators that splits
the fundamental fields according to their individual degrees of freedom. With
this new basis, the attainment of the propagators is remarkably simplified and
the identification of the physical and unphysical modes gets a new insight. Our
conclusion is that the only tachyon- and ghost-free model is the
Einstein-Hilbert action added up by the Chern-Simons term with a time-like
vector of the type . Spectral consistency imposes taht
the Ricci-Cotton term must be switched off. We then infer that gravity with
Lorentz-symmetry violation imposes a drastically different constraint on the
background if compared to usual gauge theories whenever conditions for
suppression of tachyons and ghosts are required.Comment: 15 pages. It coincides with the version published in Phys. Rev.
System control of an autonomous planetary mobile spacecraft
The goal is to suggest the scheduling and control functions necessary for accomplishing mission objectives of a fairly autonomous interplanetary mobile spacecraft, while maximizing reliability. Goals are to provide an extensible, reliable system conservative in its use of on-board resources, while getting full value from subsystem autonomy, and avoiding the lure of ground micromanagement. A functional layout consisting of four basic elements is proposed: GROUND and SYSTEM EXECUTIVE system functions and RESOURCE CONTROL and ACTIVITY MANAGER subsystem functions. The system executive includes six subfunctions: SYSTEM MANAGER, SYSTEM FAULT PROTECTION, PLANNER, SCHEDULE ADAPTER, EVENT MONITOR and RESOURCE MONITOR. The full configuration is needed for autonomous operation on Moon or Mars, whereas a reduced version without the planning, schedule adaption and event monitoring functions could be appropriate for lower-autonomy use on the Moon. An implementation concept is suggested which is conservative in use of system resources and consists of modules combined with a network communications fabric. A language concept termed a scheduling calculus for rapidly performing essential on-board schedule adaption functions is introduced
Universal geometrical scaling of the elliptic flow
The presence of scaling variables in experimental observables provide very
valuable indications of the dynamics underlying a given physical process. In
the last years, the search for geometric scaling, that is the presence of a
scaling variable which encodes all geometrical information of the collision as
well as other external quantities as the total energy, has been very active.
This is motivated, in part, for being one of the genuine predictions of the
Color Glass Condensate formalism for saturation of partonic densities. Here we
extend these previous findings to the case of experimental data on elliptic
flow. We find an excellent scaling for all centralities and energies, from RHIC
to LHC, with a simple generalization of the scaling previously found for other
observables and systems. Interestingly the case of the photons, difficult to
reconcile in most formalisms, nicely fit the scaling curve. We discuss the
possible interpretations of this finding in terms of initial or final state
effects.Comment: 6 pages, 4 figures, accepted for publication in Phys Rev
PLAN-IT: Scheduling assistant for solar system exploration
A frame-based expert scheduling system shell, PLAN-IT, is developed for spacecraft scheduling in the Request Integration Phase, using the Comet Rendezvous Asteroid Flyby (CRAF) mission as a development base. Basic, structured, and expert scheduling techniques are reviewed. Data elements such as activity representation and resource conflict representation are discussed. Resource constraints include minimum and maximum separation times between activities, percentage of time pointed at specific targets, and separation time between targeted intervals of a given activity. The different scheduling technique categories and the rationale for their selection are also considered
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