1,718 research outputs found
Photon Propagation as a Probe for Fundamental Physics
No full textIn this thesis we show how light propagation can be used in order to
constrain particle physics models beyond the Standard Model. We study in
particular the effects of non standard physics on the polarization of cosmic
microwave background radiation and on the flux of ultrahigh energy γ-rays
(Eγ > 1019 eV).
In the first part we discuss the effects on cosmic microwave background
polarization of coupling between photons and pseudoscalar fields acting as
dark matter (e.g. axions) or as dark energy (e.g. ultralight pseudo Nambu-
Goldstone bosons). In particular we describe how the public code CAMB
can be modified in order to take into account the rotation of the linear polarization
plane from last scattering surface to nowadays, produced by photon
propagation in a cosmological background of pseudoscalar particles. Polarization
power spectra are compared with the ones obtained in the widely
used approximation in which the rotation angle is assumed constant in time.
We show how polarization-polarization and temperature-polarization angular
power spectra can be very useful to constrain the coupling constant gφ
between photons and pseudoscalars.
In the second part of this thesis we use the current upper limits on the flux
of ultrahigh-energy photons in order to constrain Lorentz invariance violating
terms in the dispersion relations for elementary particles. Theories trying to
unify quantum mechanics with general relativity and many supersymmetry
models predict indeed that Lorentz symmetry has to be modified at energies
of the order of the Planck scale (1028 eV). If standard dispersion relations of
elementary particles are modified, then the propagation and therefore also
the energy spectrum of ultrahigh-energy cosmic rays can be considerably
changed. We study in particular how it is possible to constrain Lorentz
invariance violating terms for photons and electrons (suppressed both at
first and second order of the Planck mass) improving current constraints by
several orders of magnitude.
The main results are summarized in the following papers:
• F. Finelli and M. Galaverni, “Rotation of Linear Polarization Plane
and Circular Polarization from Cosmological Pseudoscalar Fields,”
arXiv:0802.4210 [astro-ph], submitted.
• M. Galaverni, F. Finelli, “Systematics of Cosmic Microwave Background
Polarization,” Internal Report IASF-BO 454/2007.
• M. Galaverni and G. Sigl, “Lorentz Violation in the Photon Sector and
Ultra-High Energy Cosmic Rays,” Phys. Rev. Lett. 100, 021102 (2008)
[arXiv:0708.1737 [astro-ph]].
• M. Galaverni and G. Sigl, “Lorentz Violation and Ultrahigh-Energy
Photons,” Phys. Rev. D 78, 063003 (2008) [arXiv:0807.1210 [astroph]]
Rotation of Linear Polarization Plane and Circular Polarization from Cosmological Pseudoscalar Fields
No full textWe discuss the rotation of the linear polarization plane and the production of circular polarization generated by a cosmological pseudoscalar field. We compute analytically and numerically the propagation of the Stokes parameters from the last scattering surface for an oscillating and a monotonic decreasing pseudoscalar field. For the models studied in this paper, we show the comparison between the widely used approximation in which the linear polarization rotation angle is constant in time and the exact result. © 2009 The American Physical Society
Lorentz Violation in the Photon Sector and Ultra-High Energy Cosmic Rays
No full textLorentz symmetry breaking at very high energies may lead
to photon dispersion relations of the form
with new terms suppressed by a power of the Planck mass . We show
that first and second order terms of size
and ,
respectively, would lead to a photon component in cosmic rays above
eV that should already have been detected.
This suggests that LI breaking suppressed up to second order
in the Planck scale are unlikely to be phenomenologically viable
for photon
Lorentz Violation and Ultrahigh-Energy Photons.
No full textThe propagation of photons, electrons and positrons at ultra-high energies
above eV can be changed considerably if the dispersion relations
of these particles are modified by terms suppressed by powers of the Planck scale.
We recently pointed out that the current non-observation of photons in the
ultra-high energy cosmic ray flux at such energies can put strong constraints
on such modified dispersion relations. In the present work we generalize these
constraints to all three Lorentz invariance breaking parameters that can occur
in the dispersion relations for photons, electrons and positrons at first and second
order suppression with the Planck scale. We also show how the excluded regions in these three-dimensional
parameter ranges would be extended if ultra-high energy photons are detected in the future
Light Bending as a Probe of the Nature of Dark Energy
No full textWe study the bending of light for static spherically symmetric (SSS) space-times which include a dark energy contribution. Geometric dark energy models generically predict a correction to the Einstein angle written in terms of the distance to the closest approach, whereas a cosmological constant does not.
While dark energy is associated with a repulsive force in cosmological context, its effect on null geodesics in SSS space-times can be attractive as for the Newtonian term. This dark energy contribution may not be negligible with respect to the Einstein prediction in lensing involving clusters of galaxies. Strong lensing may therefore be useful to distinguish from other dark energy models
TUTELA DEL LAVORO E LIBERTA' D'IMPRESA NEI PROCESSI DI ESTERNALIZZAZIONE
No full textL’elaborato analizza le conseguenze lavoristiche della successione fra imprenditori, muovendo da una ricognizione delle varie tipologie di esternalizzazione con le relative esigenze e principali criticità.
L’indagine si concentra in primo luogo sul trasferimento d’azienda, esaminando la normativa e la giurisprudenza europee per passare poi alla disciplina di diritto interno, alle procedure sindacali e a uno specifico focus sul trasferimento delle aziende in crisi.
Successivamente l’autore si sofferma sull’appalto, prendendone in particolare considerazione gli indici di genuinità, i criteri di distinzione dalla somministrazione illecita di manodopera e la tutela delle maestranze in caso di avvicendamento fra imprese.
Da ultimo, la ricerca approfondisce le c.d. “clausole sociali”, sia di prima che di seconda generazione, valutandone la compatibilità con il diritto eurounitario e con la costituzione nonché riflettendo sui possibili rimedi in caso di loro violazione.The author analyzes the labour consequences of the succession between entrepreneurs, starting from a recognition of the various types of outsourcing with the related needs and main critical issues.
The survey focuses primarily on the transfer of businesses, examining European legislation and case-law and then moving on to internal legislation, trade union procedures and a specific focus on the transfer of companies in crisis.
The author then dwells on the contract, taking into account in particular the indications of authenticity, the criteria of distinction from the illicit administration of labour and the protection of workers in the event of turnover between companies.
Finally, the research deepens the "social clauses", both first and second generation, assessing their compatibility with European law and with the constitution and reflecting on possible remedies in case of their violation
Ultra Low Carbon Vehicles: New Parameters for Automotive Design
No full textAs the influence of vehicle emissions on our environment has become better understood, the UK government has recently placed urgent emphasis on the implementation of low carbon
technologies in the automotive industry through: the UK Low Carbon Industrial Strategy. The overall objective is to offer big incentives to consumers and support for the development of infrastructure and engineering solutions. This scheme however does not consider how the development of functional and experiential user value might drive consumer demand, contributing to the adoption of low carbon vehicles (LCVs) in the mass market.
With the emergence of the North East of England as the UK’s first specialised region for the development of ultra-low carbon vehicles (ULCVs), ONE North East, as a development agency for the region's economic and business development, and Northumbria University Ideas-lab have supported a project to facilitate innovation through the collaboration of technology, research and development (R&D) and business. The High Value Low Carbon (HVLC) project aims to envisage
new user value made possible by the integration of low carbon vehicle platforms with new process and network technologies. The HVLC consortium represents vehicle manufacturers and their suppliers as well as technology based companies and through an ongoing process of design concept generation the project offers a hub for innovation led enterprise.
Whilst new technological developments in areas such as power generation, nano materials, hydrogen fuel cells, printed electronics and networked communications will all impact on future automotive design, the mass adoption of low carbon technologies represents a paradigm shift for the motorist. This paper aims to describe how the mapping of new parameters will lead to new transport scenarios that will create the space for new collaborative research on user experiences supported by innovative technologies and related services
Recommended from our members
Matteo Maria Boiardo (1441-1494)
No full textMatteo Maria Boiardo – contemporary of Sir Thomas Malory and forerunner of Shakespeare, Spenser, Milton, Cervantes, Tolkien, and C.S. Lewis – is best known as the author of the Orlando Innamorato [Orlando in Love], a poem in ottava rima organically merging Carolingian epic and Arthurian romance. He was also a lyric and pastoral poet, playwright, and translator of classical texts into the Italian vernacular. Matteo was active in Italy during the years of 1463 throughout 1494, the year of his death
Uno sguardo all'Est. Lavoro e diritti fondamentali in Russia e negli altri Paesi della Comunità di Stati indipendenti
No full textNel contributo l'autore, dopo aver esaminato i diritti fondamentali del lavoro presenti nelle Costituzioni dei Paesi della Comunità di Stati indipendenti, si sofferma sul diritto del lavoro russo. La trattazione, a carattere diacronico, abbraccia i rami principali del diritto del lavoro: il rapporto individuale, le relazioni collettive, il mercato del lavoro. L'autore rileva una sorprendente continuità nelle linee essenziali del diritto del lavoro russo, pur nel susseguirsi di sistemi socioeconomici completamente diversi. Egli conclude che il diritto del lavoro russo appartiene saldamente alla matrice europea della materia.The contribution of the author starts by examining fundamental labour rights recognised by the Constitutions of the Countries of the Community of Independent States. Then the author focuses upon Russian Labour Law, going through the history of the main branches of the discipline: the individual relationship, industrial relations, the labour market. The article finds a surprising continuity in the essential lines of Russian Labour Law, in spite of the completely different socio-economic systems that were experimented in Russia during the twentieth century. The author concludes that Russian Labour Law clearly belongs to the European matrix of the discipline
- …
