5,284 research outputs found
Trace anomalies and chiral Ward identities
In a simple abelian spinor field theory, the canonical trace identities for
certain axial-vector and axial-scalar operators are reexamined in dimensional
regularization, some disagreements with previous results are found and an
interesting new phenomenon is observed and briefly discussed.Comment: 4 pages, no figure, typos remove
Scale-free networks with an exponent less than two
We study scale free simple graphs with an exponent of the degree distribution
less than two. Generically one expects such extremely skewed networks
-- which occur very frequently in systems of virtually or logically connected
units -- to have different properties than those of scale free networks with
: The number of links grows faster than the number of nodes and they
naturally posses the small world property, because the diameter increases by
the logarithm of the size of the network and the clustering coefficient is
finite. We discuss a simple prototype model of such networks, inspired by real
world phenomena, which exhibits these properties and allows for a detailed
analytical investigation
Warped Phenomenology
We explore the phenomenology associated with the recently proposed localized
gravity model of Randall and Sundrum where gravity propagates in a
5-dimensional non-factorizable geometry and generates the 4-dimensional
weak-Planck scale hierarchy by an exponential function of the compactification
radius, called a warp factor. The Kaluza-Klein tower of gravitons which emerge
in this scenario have strikingly different properties than in the factorizable
case with large extra dimensions. We derive the form of the graviton tower
interactions with the Standard Model fields and examine their direct production
in Drell-Yan and dijet events at the Tevatron and LHC as well as the KK
spectrum line-shape at high-energy linear \epem colliders. In the case where
the first KK excitation is observed, we outline the procedure to uniquely
determine the parameters of this scenario. We also investigate the effect of KK
tower exchanges in contact interaction searches. We find that present
experiments can place meaningful constraints on the parameters of this model.Comment: 14 pages, LaTex, 3 fig
TeV-scale electron Compton scattering in the Randall-Sundrum scenario
The spin-2 graviton excitations in the Randall-Sundrum gravity model provides
a t-channel contribution to electron Compton scattering which competes
favourably with the standard QED contributions. The phenomenological
implications of these contributions to the unpolarized and polarized
cross-sections are evaluated.Comment: 11 pages, 5 figure
Amplitudes and Spinor-Helicity in Six Dimensions
The spinor-helicity formalism has become an invaluable tool for understanding
the S-matrix of massless particles in four dimensions. In this paper we
construct a spinor-helicity formalism in six dimensions, and apply it to derive
compact expressions for the three, four and five point tree amplitudes of
Yang-Mills theory. Using the KLT relations, it is a straightforward process to
obtain amplitudes in linearized gravity from these Yang-Mills amplitudes; we
demonstrate this by writing down the gravitational three and four point
amplitudes. Because there is no conserved helicity in six dimensions, these
amplitudes describe the scattering of all possible polarization states (as well
as Kaluza-Klein excitations) in four dimensions upon dimensional reduction. We
also briefly discuss a convenient formulation of the BCFW recursion relations
in higher dimensions.Comment: 26 pages, 2 figures. Minor improvements of the discussio
High Energy Photon-Photon Collisions at a Linear Collider
High intensity back-scattered laser beams will allow the efficient conversion
of a substantial fraction of the incident lepton energy into high energy
photons, thus significantly extending the physics capabilities of an
electron-electron or electron-positron linear collider. The annihilation of two
photons produces C=+ final states in virtually all angular momentum states. The
annihilation of polarized photons into the Higgs boson determines its
fundamental two-photon coupling as well as determining its parity. Other novel
two-photon processes include the two-photon production of charged lepton pairs,
vector boson pairs, as well as supersymmetric squark and slepton pairs and
Higgstrahlung. The one-loop box diagram leads to the production of pairs of
neutral particles. High energy photon-photon collisions can also provide a
remarkably background-free laboratory for studying possibly anomalous
collisions and annihilation. In the case of QCD, each photon can materialize as
a quark anti-quark pair which interact via multiple gluon exchange. The
diffractive channels in photon-photon collisions allow a novel look at the QCD
pomeron and odderon. Odderon exchange can be identified by looking at the heavy
quark asymmetry. In the case of electron-photon collisions, one can measure the
photon structure functions and its various components. Exclusive hadron
production processes in photon-photon collisions test QCD at the amplitude
level and measure the hadron distribution amplitudes which control exclusive
semi-leptonic and two-body hadronic B-decays.Comment: Invited talk, presented at the 5th International Workshop On
Electron-Electron Interactions At TeV Energies, Santa Cruz, California, 12-14
December 200
Preparación de nuevas nanoemulsiones a partir de aceite rico en omega-3
This work aimed to produce stabilized omega-3-rich oil in a water nanoemulsion using a high-pressure homogenizer (HPH). Studies were carried out on the effects of the type of the emulsifier and its conÂcentration, HPH conditions (pressure and number of passes inside the homogenization chamber) as well as continuous phase viscosity on the polydispersity index (PDI) and mean droplet size of the nanoemulsion were carried out. The impact of rosemary extract on the oxidative stability of the emulsion was also monitored. Results showed that small molecular weight emulsifiers gave small droplet size and vice versa. In addition, the results revealed that a parallel decrease in mean droplet diameter was observed with increases in emulsifier concentraÂtion, homogenization cycles (passes) and homogenization pressure. Furthermore, when the viscosity of the aqueÂous phase increased, a slight non-significant and irregular fluctuation in the droplet size was detected. The results demonstrated that rosemary extract enhanced the oxidative stability of this nanoemulsion. Our results could help in formulating stabilized omega-3-enriched nanoemulsions that could be applied in different food stuffs.Este trabajo tuvo como objetivo producir nanoemulsiones de aceite rico en omega-3 estabilizado en agua usando un homogeneizador de alta presión (HPH). Estudiando los efectos del tipo de emulsionante y su concentración, se llevaron a cabo las condiciones de HPH (presión y número de pasadas dentro de la cámara de homogeneización), asà como la viscosidad de fase continua en el Ãndice de polidispersidad (PDI) y el tamaño medio de gota de la nanoemulsión. También se siguió el impacto de la adición de extracto de romero sobre la estabilidad oxidativa de la emulsión. Los resultados mostraron que los emulsionantes de peso molecular pequeño dieron un tamaño de gota pequeño y viceversa. Los resultados también revelaron que hay una disminución paralela en el diámetro medio de las gotitas con el aumento de la concentración de emulsionante, los ciclos de homogeneización (pases) y la presión de homogeneización. Además, cuando aumentó la viscosidad de la fase acuosa, se observó una ligera fluctuaÂción no significativa e irregular en el tamaño de la gota. Además, los resultados demostraron que el extracto de romero mejoró la estabilidad oxidativa de esta nanoemulsión. Nuestros resultados podrÃan ayudar a formular nanoemulsiones enriquecidas con omega-3 estabilizadas que podrÃan aplicarse en diferentes alimentos
Pseudo-axions in Little Higgs models
Little Higgs models have an enlarged global symmetry which makes the Higgs
boson a pseudo-Goldstone boson. This symmetry typically contains spontaneously
broken U(1) subgroups which provide light electroweak-singlet pseudoscalars.
Unless such particles are absorbed as the longitudinal component of
states, they appear as pseudoscalars in the physical spectrum at the
electroweak scale. We outline their significant impact on Little Higgs
phenomenology and analyze a few possible signatures at the LHC and other future
colliders in detail. In particular, their presence significantly affects the
physics of the new heavy quark states predicted in Little Higgs models, and
inclusive production at LHC may yield impressive diphoton resonances.Comment: 28 pages, 9 figs., accepted to PRD; footnote added, typos correcte
A heavy Higgs boson from flavor and electroweak symmetry breaking unification
We present a unified picture of flavor and electroweak symmetry breaking
based on a nonlinear sigma model spontaneously broken at the TeV scale. Flavor
and Higgs bosons arise as pseudo-Goldstone modes. Explicit collective symmetry
breaking yields stable vacuum expectation values and masses protected at one
loop by the little-Higgs mechanism. The coupling to the fermions generates
well-definite mass textures--according to a U(1) global flavor symmetry--that
correctly reproduce the mass hierarchies and mixings of quarks and leptons. The
model is more constrained than usual little-Higgs models because of bounds on
weak and flavor physics. The main experimental signatures testable at the LHC
are a rather large mass m_{h^0} = 317\pm 80 GeV for the (lightest) Higgs boson
and a characteristic spectrum of new bosons and fermions at the TeV scale.Comment: 5 page
Momentum Amplituhedron meets Kinematic Associahedron
© The Author(s) 2021.This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited (https://creativecommons.org/licenses/by/4.0/).In this paper we study a relation between two positive geometries: the momen- tum amplituhedron, relevant for tree-level scattering amplitudes in N = 4 super Yang-Mills theory, and the kinematic associahedron, encoding tree-level amplitudes in bi-adjoint scalar φ 3 theory. We study the implications of restricting the latter to four spacetime dimensions and give a direct link between its canonical form and the canonical form for the momentum amplituhedron. After removing the little group scaling dependence of the gauge theory, we find that we can compare the resulting reduced forms with the pull-back of the associahedron form. In particular, the associahedron form is the sum over all helicity sectors of the reduced momentum amplituhedron forms. This relation highlights the common sin- gularity structure of the respective amplitudes; in particular, the factorization channels, corresponding to vanishing planar Mandelstam variables, are the same. Additionally, we also find a relation between these canonical forms directly on the kinematic space of the scalar theory when reduced to four spacetime dimensions by Gram determinant constraints. As a by-product of our work we provide a detailed analysis of the kinematic spaces relevant for the four-dimensional gauge and scalar theories, and provide direct links between them.Peer reviewe
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