3,595 research outputs found
A Simple-Minded Unitarity Constraint and an Application to Unparticles
Unitarity, a powerful constraint on new physics, has not always been properly
accounted for in the context of hidden sectors. Feng, Rajaraman and Tu have
suggested that large (pb to nb) multi-photon or multi-lepton sugnals could be
generated at the LHC through the three-point functions of a
conformally-invariant hidden sector (an "unparticle" sector.) Because of the
conformal invariance, the kinematic distributions are calculable. However, the
cross-sections for many such processes grow rapidly with energy, and at some
high scale, to preserve unitarity, conformal invariance must break down.
Requiring that conformal invariance not be broken, and that no signals be
already observed at the Tevatron, we obtain a strong unitarity bound on
multi-photon events at the (10 TeV) LHC. For the model of Feng et al., even
with extremely conservative assumptions, cross-sections must be below 25 fb,
and for operator dimension near 2, well below 1 fb. In more general models,
four-photon signals could still reach cross-sections of a few pb, though bounds
below 200 fb are more typical. Our methods apply to a wide variety of other
processes and settings
Analysis of the stellar population in the central area of the HII region Sh 2-284
There is a lack of state-of-the-art information on very young open clusters,
with implications for determining the structure of the Galaxy. Our main
objective is to study the timing and location of the star formation processes
which yielded the generation of the giant HII region Sh 2-284. The analysis is
based on UBVRcIc CCD measurements and JHKs photometry in the central part of
the HII region, where the cluster Dolidze 25 is located.The determination of
cluster distance, reddening and age is carried out through comparison with
ZAMS, post-MS and PMS isochrones. Reference lines for metallicity Z=0.004 are
used, in agreement with spectroscopic metallicity determination published for
several cluster members. The results are: E(B-V)=0.78+-0.02, M=12.8+-0.2,
LogAge(yr)=6.51+-0.07. A PMS member sequence is proposed, coeval within the
errors with the post-MS cluster age (LogAge(yr)=6.7+-0.2). The mass function
for this PMS population in the mass range above 1.3-3.5 Msun is well fitted by
a Salpeter mass function.The presence of a different star generation in the
cluster with a distinctly older age, around 40 Myr, is suggested. The NIR
results indicate a large number of sources with H-Ks excess, practically
distinct from the optical PMS candidate members.
The distance determined for the cluster is distinctly lower than previously
published values. This result originates in the consistent use of low
metallicity models for ZAMS fitting, applying published metallicity values for
the cluster.Comment: gzipped tar file: 1 aa.cls, 1 tex file, 1 bbl file, 13 figures.
Accepted in Astronomy & Astrophysics (9.11.2009
Harmonic mappings and conformal minimal immersions of Riemann surfaces into RN
We prove that for any open Riemann surface N, natural number N ≥ 3, non-constant harmonic map h:N→R N−2 and holomorphic 2-form H on N , there exists a weakly complete harmonic map X=(Xj)j=1,…,\scN:N→R\scN with Hopf differential H and (Xj)j=3,…,\scN=h. In particular, there exists a complete conformal minimal immersion Y=(Yj)j=1,…,\scN:N→R\scN such that (Yj)j=3,…,\scN=h . As some consequences of these results (1) there exist complete full non-decomposable minimal surfaces with arbitrary conformal structure and whose generalized Gauss map is non-degenerate and fails to intersect N hyperplanes of CP\scN−1 in general position. (2) There exist complete non-proper embedded minimal surfaces in R\scN, ∀\scN>3.Ministerio de Ciencia y TecnologÃa MTM2007-61775Ministerio de Ciencia y TecnologÃa MTM2007-64504Junta de AndalucÃa P09-FQM-508
Complete minimal surfaces and harmonic functions
We prove that for any open Riemann surface N and any non constant harmonic function
h : N → R, there exists a complete conformal minimal immersion X : N → R3 whose third
coordinate function coincides with h.
As a consequence, completeminimal surfaceswith arbitrary conformal structure andwhose Gauss
map misses two points are constructed.Ministerio de Educación y Ciencia MTM2007-61775Ministerio de Educación y Ciencia MTM2007-64504Junta de AndalucÃa P06-FQM-01642
Unitarity, analyticity, dispersion relations and resonances in strongly interacting , and scattering
If the Electroweak Symmetry Breaking Sector turns out to be strongly
interacting, the actively investigated effective theory for longitudinal gauge
bosons plus Higgs can be efficiently extended to cover the regime of saturation
of unitarity (where the perturbative expansion breaks down). This is achieved
by dispersion relations, whose subtraction constants and left cut contribution
can be approximately obtained in different ways giving rise to different
unitarization procedures. We illustrate the ideas with the Inverse Amplitude
Method, one version of the N/D method and another improved version of the
K-matrix. In the three cases we get partial waves which are unitary, analytical
with the proper left and right cuts and in some cases poles in the second
Riemann sheet that can be understood as dynamically generated resonances. In
addition they reproduce at Next to Leading Order (NLO) the perturbative
expansion for the five partial waves not vanishing (up to J=2) and they are
renormalization scale () independent. Also the unitarization formalisms
are extended to the coupled channel case. Then we apply the results to the
elastic scattering amplitude for the longitudinal components of the gauge
bosons at high energy. We also compute and the
inelastic process which are coupled to the elastic
channel for custodial isospin . We numerically compare the three methods
for various values of the low-energy couplings and explain the reasons for the
differences found in the partial wave. Then we study the resonances
appearing in the different elastic and coupled channels in terms of the
effective Lagrangian parameters.Comment: 45 pages, 28 figure
One-loop and scattering from the Electroweak Chiral Lagrangian with a light Higgs-like scalar
By including the recently discovered Higgs-like scalar in the
Electroweak Chiral Lagrangian, and using the Equivalence Theorem, we carry out
the complete one-loop computation of the elastic scattering amplitude for the
longitudinal components of the gauge bosons at high energy. We also
compute and the inelastic process
, and identify the counterterms needed to cancel
the divergences, namely the well known and chiral parameters plus
three additional ones only superficially treated in the literature because of
their dimension 8. Finally we compute all the partial waves and discuss the
limitations of the one-loop computation due to only approximate unitarity.Comment: 28 pages, 19 plots, 9 Feynman-diagram sets This version revised and
accepted in JHE
Possible new resonance from - interchannel coupling
We propose and theoretically study a possible new resonance caused by strong
coupling between the Higgs-Higgs and the W_L W_L (Z_L Z_L) scattering channels,
without regard to the intensity of the elastic interaction in either channel at
low energy (that could be weak as in the Standard Model). We expose this
channel-coupling resonance from unitarity and dispersion relations encoded in
the Inverse Amplitude Method, applied to the Electroweak Chiral Lagrangian with
a scalar Higgs.Comment: 4 pages, 7 figure
Coupling WW, ZZ unitarized amplitudes to in the TeV region
We define and calculate helicity partial-wave amplitudes for processes
linking the Electroweak Symmetry Breaking Sector (EWSBS) to ,
employing (to NLO) the Higgs-EFT (HEFT) extension of the Standard Model and the
Equivalence Theorem, while neglecting all particle masses. The resulting
amplitudes can be useful in the energy regime ().
We also deal with their unitarization so that resonances of the EWSBS can
simultaneously be described in the initial or final states. Our
resulting amplitudes satisfy unitarity, perturbatively in , but for all
values. In this way we improve on the HEFT that fails as interactions
become stronger with growing and provide a natural framework for the decay
of dynamically generated resonances into , and pairs.Comment: 23 pages, 9 figure
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