arXiv subjects

R. Rodrigues da Silva

Publications and source records attributed to R. Rodrigues da Silva.

14 recordsLinked to original sources

arXiv2016

The $ρ(1S,2S)$, $ψ(1S,2S)$, $Υ(1S,2S)$ and $ψ_t(1S,2S)$ mesons in a double pole QCD Sum Rule

We use the method of double pole QCD sum rule which is basically a fit with two exponentials of the correlation function, where we can extract the masses and decay constants of mesons as a function of the Borel mass. We apply this method to study the mesons: $ρ(1S,2S)$, $ψ(1S,2S)$, $Υ(1S,2S)$ and $ψ_t(1S,2S)$. We also present predictions for the toponiuns masses $ψ_t(1S,2S)$ of m(1S)=357 GeV and m(2S)=374 GeV.

hep-ph↗

arXiv2015

Kepler rapidly rotating giant stars

Rapidly rotating giant stars are relatively rare and may represent important stages of stellar evolution, resulting from stellar coalescence of close binary systems or accretion of sub-stellar companions by their hosting stars. In the present letter we report 17 giant stars observed in the scope of the Kepler space mission exhibiting rapid rotation behavior. For the first time the abnormal rotational behavior for this puzzling family of stars is revealed by direct measurements of rotation, namely from photometric rotation period, exhibiting very short rotation period with values ranging from 13 to 55 days. This finding points for remarkable surface rotation rates, up to 18 times the Sun rotation. These giants are combined with 6 other recently listed in the literature for mid-IR diagnostic based on WISE information, from which a trend for an infrared excess is revealed for at least a half of the stars, but at a level far lower than the dust excess emission shown by planet-bearing main-sequence stars.

astro-ph.SR↗

arXiv2012

Exotic Behavior of Heavy-Flavored Meson Matter

In this work, we study the thermodynamic behavior of heavy-flavored meson matter in the framework of $(σ,ω)$-meson-exchange model in relativistic mean field theory. We find a decreasing of the effective masses of $D$ and $B$ mesons as the temperature increases. By using the effective mass and maximum value of dissociation temperatures available from lattice QCD, the masses of the bound states $D \bar{D}$ and $B \bar{B}$ are estimated in 2 MeV for both molecules. For the $B$-meson matter, the pressure presents an exotic behavior, being negative for temperatures above 6.6 times the deconfinement transition temperature $T_c$. In addition, the ratio of pressure to energy density is similar to the value predicted for systems that behave as dark energy matter.

hep-ph↗

arXiv2012

The D-\bar{D} matter in Walecka's mean field theory

We study the mesons matter D-\bar{D} in the framework of sigma and omega meson exchange model using Walecka's mean field theory. We choose the equal number of D and anti-D meson then we get =0 and the field sigma exhibits a critical temperature around 1.2 GeV. We investigate effective mass, pressure, energy density and energy per pair. We conclude that this matter is a gas and these results are not favorable for the existence of D-\bar{D} bound state. Note: in arXiv:1211.5505 this interpretation has been updated where these results are favorable for the existence of $D-\bar{D}$ bound state.

hep-ph↗

arXiv2008

The meson $Z^+(4430)$ as a tetraquark state

We test the validity of the QCD sum rules applied to the meson $Z^+(4430)$, by considering a diquark-antidiquark type of current with $J^{P}=0^{-}$ and with $J^{P}=1^{-}$. We find that, with the studied currents, it is possible to find an acceptable Borel window. In such a Borel window we have simultaneously a good OPE convergence and a pole contribution which is bigger than the continuum contribution. We get $m_Z=(4.52\pm0.09)\GeV$ and $m_Z=(4.84\pm0.14)\GeV$ for the currents with $J^{P}=0^{-}$ and $J^{P}=1^{-}$ respectively. We conclude that the QCD sum rules results favors $J^{P}=0^{-}$ quantum numbers for the $Z^+(4430)$ meson.

hep-ph↗

arXiv2007

Do the QCD sum rules support four-quark states?

We test the validity of the QCD sum rules applied to the light scalar mesons, the charmed mesons $D_{s0}(2317)$ and $D_{s1} (2460)$, and the X(3872) axial meson, considered as tetraquark states. We find that, with the studied currents, it is possible to find an acceptable Borel window only for the X(3872) meson. In such a Borel window we have simultaneouly a good OPE convergence and a pole contribution which is bigger than the continuum contribution. We interpret these results as a strong argument against the assignment of a tetraquark structure for the light scalars and the $D_{s0}(2317)$ and $D_{s1} (2460)$ mesons.

hep-ph↗

arXiv2005

Pentaquark Decay in QCD Sum Rules

In a diquark-diquark-antiquark picture of the pentaquark we study the decay $Θ\to K^{+} n$ within the framework of QCD sum rules. After evaluation of the relevant three-point function, we extract the coupling $g_{ΘnK}$ which is directly related to the pentaquark width. Restricting the decay diagrams to those with color exchange between the meson-like and baryon-like clusters reduces the coupling constant by a factor of four. Whereas a small decay width might be possible for a positive parity pentaquark, it seems difficult to explain the measured width for a pentaquark with negative parity.

hep-ph↗

arXiv2005

Pentaquark Decay Width in QCD Sum Rules

In a diquark-diquark-antiquark picture of the pentaquark we study the decay $Θ\rightarrow K^{+} n$ within the framework of QCD sum rules. After evaluation of the relevant three-point function, we extract the coupling $g_{ΘnK}$ which is directly related to the pentaquark width. Restricting the decay diagrams to those with color exchange between the meson-like and baryon-like clusters reduces the coupling constant by a factor of four. Whereas a small decay width might be possible for a positive parity pentaquark, it seems difficult to explain the measured width for a pentaquark with negative parity.

hep-ph↗

arXiv2004

A Comparative Study of Pentaquark Interpolating Currents

In a diquark-diquark-antiquark picture of pentaquarks, we use two interpolating currents to calculate the mass of the recently measured $Ξ^{--}$ state in the framework of QCD sum rules. We show that, even though yielding similar values for $m_{Ξ^{--}}$ (and close to the experimental value), these currents differ from each other in what concerns the strength of the pole, convergence of the OPE and sensitivity to the continuum threshold parameter.

hep-ph↗

arXiv2004

$J/ψ$ couplings to open charm mesons from QCD sum rules

We employ QCD sum rules to calculate the $J/ψ$ form factors and coupling constants with charmed mesons, by studying three-point correlation functions. In particular we consider the $J/ψD^*D$ and $J/ψDD$ vertices. We determine the momentum dependence of the form factors for kinematical conditions where J/ψ, D or D^* are off-shell. Extrapolating to the pole of each one of the so obtained form factors, we determine the coupling constants. For both couplings our results (within the errors) are compatible with estimates based on constituent quark model.

hep-ph↗

arXiv2003

Are $Θ^+$ and the Roper resonance diquark-diquark-antiquark states?

We consider a $[ud]^2\bar{s}$ current in the QCD sum rule framework to study the mass of the recently observed pentaquark state $Θ^+(1540)$, obtaining good agreement with the experimental value. We also study the mass of the pentaquark $[ud]^2\bar{d}$. Our results are compatible with the interpretation of the $[ud]^2\bar{d}$ state as being the Roper resonance N(1440), as suggested by Jaffe and Wilczek.

hep-ph↗

arXiv2003

The $J/ψDD^*$ vertex

We employ QCD sum rules to calculate the $J/ψDD^*$ form factors and coupling constant by studying the three-point $J/ψD^*D$ correlation function. We find that the momentum dependence of the form factor depends on the off-shell meson. We get a value for the coupling which is in agreement with estimates based on constituent quark model.

hep-ph↗

arXiv2002

The $J/ψD D$ Vertex in QCD Sum Rules

The $J/ψD D$ form factor is evaluated in a QCD sum rule calculation for both $D$ and $J/ψ$ off-shell mesons. We study the double Borel sum rule for the three point function of two pseudoscalar and one vector meson current. We find that the momentum dependence of the form factors is different if the $D$ or the $J/ψ$ meson is off-shell, but they lead to the same coupling constant in the $J/ψD D$ vertex.

hep-ph↗

arXiv2000

Generalized Field Theoretical Approach to General Relativity and Conserved Quantities in Anti-de Sitter Spacetimes

A new prescription to calculate the total energies and angular momenta of asymptotically $(d+1)$-dimensional anti-de Sitter spacetimes is proposed. The method is based on an extension of the field theoretical approach to General Relativity to the case where there is an effective cosmological constant. A $(d-1)$-form $Ω$ is exhibited which, when integrated on asymptotic $(d-1)$-dimensional boundary surfaces, yields the values of those conserved quantities. The calculations are gauge independent once asymptotic conditions are not violated . Total energies and angular momenta of some known solutions in four and five dimensions are calculated agreeing with standard results.

gr-qc↗