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Rogerio Rosenfeld

Publications and source records attributed to Rogerio Rosenfeld.

50 records · Page 3Linked to original sources
arXiv2004

Variable-Mass Dark Matter and the Age of the Universe

Models with variable-mass particles, called VAMPs, have been proposed as a solution to the cosmic coincidence problem that plagues dark energy models. In this contribution we make a short description of this class of models and explore some of its observational consequences. In particular, we show that fine tuning is still required in this scenario and that the age of the Universe is considerably larger than in the standard Lambda-CDM model.

astro-ph↗
arXiv2004

Age constraints and fine tuning in variable-mass particle models

VAMP (variable-mass particles) scenarios, in which the mass of the cold dark matter particles is a function of the scalar field responsible for the present acceleration of the Universe, have been proposed as a solution to the cosmic coincidence problem, since in the attractor regime both dark energy and dark matter scale in the same way. We find that only a narrow region in parameter space leads to models with viable values for the Hubble constant and dark energy density today. In the allowed region, the dark energy density starts to dominate around the present epoch and consequently such models cannot solve the coincidence problem. We show that the age of the Universe in this scenario is considerably higher than the age for noncoupled dark energy models, and conclude that more precise independent measurements of the age of the Universe would be useful in distinguishing between coupled and noncoupled dark energy models.

astro-ph↗
arXiv2004

Testing Option Pricing with the Edgeworth Expansion

There is a well developed framework, the Black-Scholes theory, for the pricing of contracts based on the future prices of certain assets, called options. This theory assumes that the probability distribution of the returns of the underlying asset is a gaussian distribution. However, it is observed in the market that this hypothesis is flawed, leading to the introduction of a fudge factor, the so-called volatility smile. Therefore, it would be interesting to explore extensions of the Black-Scholes theory to non-gaussian distributions. In this contribution we provide an explicit formula for the price of an option when the distributions of the returns of the underlying asset is parametrized by an Edgeworth expansion, which allows for the introduction of higher independent moments of the probability distribution, namely skewness and kurtosis. We test our formula with options in the brazilian and american markets, showing that the volatility smile can be reduced. We also check whether our approach leads to more efficient hedging strategies of these instruments.

cond-mat↗
arXiv2003

gg-->H-->tau tau at the Upgraded Fermilab Tevatron

We study the neutral Higgs boson production via the gluon fusion process with the $\tautau$ final state at the upgraded Fermilab Tevatron, including a complete simulation of signal channels and leading background processes. For the SM Higgs boson, this $h\to \tautau$ channel may provide important addition for the Higgs boson discovery in the mass range 120-140 GeV. In minimal supersymmetric models, natural enhancement for the signal rate over the SM expectation makes the $h,H,A\to \tautau$ signal observable for large $\tanβ$ and low $M_A$, which may lead to full coverage for SUSY Higgs parameters at the Tevatron with a moderate integrated luminosity.

hep-ph↗
arXiv2002

Fine Tuning in Quintessence Models with Exponential Potentials

We explore regions of parameter space in a simple exponential model of the form $V = V_0 e^{- λ\frac{Q}{M_p}}$ that are allowed by observational constraints. We find that the level of fine tuning in these models is not different from more sophisticated models of dark energy. We study a transient regime where the parameter $λ$ has to be less than $\sqrt{3}$ and the fixed point $Ω_Q = 1$ has not been reached. All values of the parameter $λ$ that lead to this transient regime are permitted. We also point out that this model can accelerate the universe today even for $λ> \sqrt{2}$, leading to a halt of the present acceleration of the universe in the future thus avoiding the horizon problem. We conclude that this model can not be discarded by current observations.

astro-ph↗
arXiv2001

Hierarchy and Anarchy in Quark Mass Matrices, or Can Hierarchy Tolerate Anarchy?

The consequences of adding random perturbations (anarchy) to a baseline hierarchical model of quark masses and mixings are explored. Even small perturbations of the order of 5% of the smallest non-zero element can already give deviations significantly affecting parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, so any process generating the anarchy should in general be limited to this order of magnitude. The regularities of quark masses and mixings thus appear to be far from a generic feature of randomness in the mass matrices, and more likely indicate an underlying order.

hep-ph↗
arXiv2001

Gauge Invariance, Color-Octet Vector Resonances and Double Technieta Production at the Tevatron

We show that the usual vector meson dominance method does not apply directly to the mixing of a color-octet vector boson (color-octet technirho) with the gluon because of gauge invariance. We propose a gauge invariant method where one works in a physical basis with mass eigenstate fields. As a result, we show that the physical technirho does not couple to two gluons, contrary to the general belief. Consequences for the production of a pair of color-octet, isosinglet technipions (technietas) at Fermilab is analysed by means of a simulation of the signal and background, including kinematical cuts. We find that the signal is too small to be observed.

hep-ph↗
arXiv1999

Tevatron Potential for Technicolor Search with Prompt Photons

We perform a detailed study of the process of single color octet isoscalar $η_T$ production at the Tevatron with $η_T \to γ+ g$ decay signature, including a complete simulation of signal and background processes. We determined a set of optimal cuts from an analysis of the various kinematical distributions for the signal and backgrounds. As a result we show the exclusion and discovery limits on the $η_T$ mass which could be established at the Tevatron for some technicolor models.

hep-ph↗
arXiv1998

Limits on a Strong Electroweak Sector from e^+ e^- -> 2gamma + missing E at LEP2

We study the process $e^+ e^- \to γγν\barν$ in the context of a strong electroweak symmetry breaking model, which can be a source of events with two photons and missing energy at LEP2. We investigate bounds on the model assuming that no deviation is observed from the Standard Model within a given experimental error.

hep-ph↗
arXiv1995

Strongly Coupled Electroweak Symmetry Breaking: Implications of Models

We discuss the phenomenology of models of dynamical electroweak symmetry breaking which attempt to generate the observed fermion mass spectrum. After briefly describing the variety of and constraints on proposed models, we concentrate on the signatures of colored pseudo-Nambu-Goldstone bosons and resonances at existing and proposed colliders. These particles provide a possibly unique signature: strongly produced resonances associated with electroweak symmetry breaking. (This is the subgroup report for the ``Electroweak Symmetry Breaking and Beyond the Standard Model" working group of the DPF Long Range Planning Study. This report will appear as a chapter in ``Electroweak Symmetry Breaking and Beyond the Standard Model", edited by T. Barklow, S. Dawson, H.E. Haber, and J. Siegrist, to be published by World Scientific.)

hep-ph↗
arXiv1994

An alternative model for the electroweak symmetry breaking sector and its signature in future e-gamma colliders

We perform a preliminary study of the deviations from the Standard Model prediction for the cross section for the process $e γ\rightarrow ν_e W γ$. We work in the context of a higgsless chiral lagrangian model that includes an extra vector resonance $V$ and an anomalous $γW V$ coupling. We find that this cross section can provide interesting constraints on the free parameters of the model once it is measured in future $e γ$ colliders.

hep-ph↗
arXiv1993

Large Multiplicity Gluon Production in QCD

We compute the approximate cross section $σ_n^{(0)}$ for producing $n-2$ {\it resolved} gluons in a gluon-gluon collision, using the Parke-Taylor formula regularized in a Lorentz invariant manner. We find, in double leading logarithm approximation, that \[ σ_{n}^{(0)} \approx \frac{1}{s} \left( \frac{N_cα_s}{2 π\sqrt{12}} \ \ln^{2} (s/s_{cut})\right)^{n-2}\ \ , \] where $\sqrt{s_{cut}}$ is the minimum invariant mass for a resolved gluon pair. There is no factor of $1/(n-2)!$ multiplying the expression. We present additional numerical results, and comment on their implications for perturbative calculations of $n$-jet cross sections at colliders.

hep-ph↗