256 research outputs found
Diphoton production at hadron colliders: transverse-momentum resummation at next-to-next-to-leading logarithmic accuracy
We consider the transverse-momentum (qT) distribution of a diphoton pair
produced in hadron collisions. At small values of qT , we resum the
logarithmically-enhanced perturbative QCD contributions up to
next-to-next-to-leading logarithmic accuracy. At intermediate and large values
of qT, we consistently combine resummation with the known next-to-leading order
perturbative result. All perturbative terms up to order \alpha_S^2 are included
in our computation which, after integration over qT, reproduces the known
next-to-next-to-leading order result for the diphoton pair production total
cross section. We present a comparison with LHC data and an estimate of the
perturbative accuracy of the theoretical calculation by performing the
corresponding variation of scales. In general we observe that the effect of the
resummation is not only to recover the predictivity of the calculation at small
transverse momentum, but also to improve substantially the agreement with the
experimental data.Comment: 17 pages, 16 figures. arXiv admin note: text overlap with
arXiv:1007.235
Unified limiting form of graviton radiation at extreme energies
We derive the limiting form of graviton radiation in gravitational scattering
at transplanckian energies () and small deflection angles. We show
that --- owing to the graviton's spin 2 --- such limiting form unifies the
soft- and Regge- regimes of emission, by covering a broad angular range, from
forward fragmentation to deeply central region. The single-exchange emission
amplitudes have a nice expression in terms of the transformation phases of
helicity amplitudes under rotations. As a result, the multiple-exchange
emission amplitudes can be resummed via an impact parameter -space
factorization theorem that takes into account all coherence effects. We then
see the emergence of an energy spectrum of the emitted radiation which, being
tuned on , is reminiscent of Hawking's radiation.
Such a spectrum is much softer than the one na\"ively expected for increasing
input energies and neatly solves a potential energy crisis. Furthermore, by
including rescattering corrections in the (quantum) factorization formula, we
are able to recover the classical limit and to find the corresponding quantum
corrections. Perspectives for the extrapolation of such limiting radiation
towards the classical collapse regime (where is of the order of the
gravitational radius ) are also discussed.Comment: 45 pages, 15 figures, new result, some corrections and additional
comment
Indirect Sensitivity to Heavy Z' Bosons at a Multi-TeV e+e- Collider
We compare the phenomenology of two models, the so-called minimal Z' and an
effective model for a SM-like Higgs realised as a composite state of a new
strong interaction, at a multi-TeV linear collider in the hypothesis that the
new physics is at a scale beyond the direct reach of the machine.Comment: 6 pages, 5 figures, to appear in the Proceedings of the International
Workshop on Future Linear Colliders LCWS201
A linear moose model with pairs of degenerate gauge boson triplets
The possibility of the existence of a strongly interacting electroweak
symmetry breaking sector, as opposed to the weakly interacting light Higgs of
the Standard Model, is not yet ruled out by experiments. In this paper we make
an extensive study of a deconstructed model (or ``moose'' model) providing a
possible effective description of such a strong symmetry breaking sector, and
show its compatibility with experimental data for a wide portion of the model
parameters space. The model is a direct generalization of the previously
proposed D-BESS model.Comment: Latex file, 17 pages, 2 figures, published versio
A naturally light dilaton
Goldstone's theorem does not apply straightforwardly to the case of
spontaneously broken scale invariance. We elucidate under what conditions a
light scalar degree of freedom, identifiable with the dilaton, can naturally
arise. Our construction can be considered an explicit dynamical solution to the
cosmological constant problem in the scalar version of gravity.Comment: v2: published versio
L'insediamento dell' antica età del bronzo di Via Neruda a Sesto Fiorentino (FI): lo sfruttamento delle risorse arboree
Master Erasmus Mundus em Quaternário e Pré-HistóriaO sítio arqueológico de Via Neruda, localizado em Sesto Fiorentino (Florença, Itália), é datável entre o final da Antiga Idade do Bronze e o início da Média Idade do Bronze. Foi objeto de uma campanha de escavações no 1999, efetuada com a direção científica da secção de Pré-História da Universidade de Siena e de Florença, sendo estas encarregadas pela Soprintendenza per i Beni Archeologici della Toscana. Ó sítio arqueológico devolveu uma quantidade de macro restos vegetais, entre os quais muitos carvões e alguns lenhos, que são o objeto de estudo na presente dissertação. Entre os carvões, alguns são consideráveis pertencentes a estruturas relativas a frequentação humana. Objetivo da presente dissertação é de perceber as conhecenças e o uso do lenho desta comunidade humana da Idade do Bronze. As análises furam feitas no Laboratório da Soprintendenza per i Beni Archeologici della Toscana. A análise antracológica dos carvões das estruturas evidenciou o uso de: Ulmus cfr. minor, Quercus spp. caducifolia, Fraxinus excelsior L., Acer cfr. campestre, Sorbus sp., Prunus cfr. avium e Populus cfr. alba. A escolha de alguns destes taxa arbóreos parece indicar uma boa conhecença das características das várias madeiras fornecidas pelas diferentes árvores identificadas (Sorbus sp., Acer cfr. campestre, Prunus cfr. avium e Populus cfr. alba); enquanto, para as outras madeiras identificadas (Sorbus sp., Acer cfr. campestre, Prunus cfr. avium e Populus cfr. alba) parecem a por em relação, mais que a escolhas especificas, ao seu abastecimento no território, provavelmente fácil, explorando as árvores das quais furam obtidos.
Os resultados finais da análise xilo-antracológica de Via Neruda permitiram de identificar além das taxa já elencadas, também: Phyllirea cfr. latifolia, Cornus cfr. mas e Abies cfr. alba.
O conjunto dos taxa identificados parece representar o testemunho de uma floresta sub-humida de planície. A única evidência de Abies cfr. alba, por causa das diferentes exigências eco edáficas desta espécie, em respeito as outras reconhecidas, parece a por em relação a um provável abastecimento em diferentes ambientes, provavelmente os das colinas nos arredores
From hidden symmetry to extra dimensions: a five dimensional formulation of the Degenerate BESS model
We consider the continuum limit of a moose model corresponding to a
generalization to N sites of the Degenerate BESS model. The five dimensional
formulation emerging in this limit is a realization of a RS1 type model with
SU(2)_L x SU(2)_R in the bulk, broken by boundary conditions and a vacuum
expectation value on the infrared brane. A low energy effective Lagrangian is
derived by means of the holographic technique and corresponding bounds on the
model parameters are obtained.Comment: Latex file, 40 pages and 5 figure
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