We calculate the strange quark content of the nucleon, <N|ss|N> − <0|ss|0> using a novel method with the MILC lattice QCD gauge ensembles. The strangeness of the nucleon is related to the interaction cross section between dark matter and ordinary nuclear matter (e.g. in detectors) in many models. Previous results for this quantity suffered from uncontrolled systematic errors and/or large statistical uncertainties. The first result using our methods was the first modern calculation of the strangeness of the nucleon[76] with good control of systematic errors and reasonably small statistical errors, greatly reducing the uncertainty in dark matter detection cross sections. A refinement of this method allows for further reduction of statistical error. On the MILC Asqtad data, we obtain <N|ss|N> = 0.637(55)(stat)(74)(sys). The results obtained from this method are consistent with those obtained from other commonly-used methods applied to the MILC data. We also calculate the disconnected part of the pion-nucleon sigma term and the intrinsic charm of the nucleon using this method. The intrinsic charm has large statistical errors but is consistent with a perturbative calculation.

O objetivo deste trabalho foi incluir o méson escalar $\\kappa$ na núvem de mésons estranhos do próton e verificar se, desta forma, a contribuição de estranheza para as suas propriedades eletromagnéticas poderia ser explicada pelo modelo da núvem mesônica. Os observáveis que quantificam tal contribuição são os fatores de forma estranhos elétrico ($G_E^s$) e magnético ($G_M^s$), que têm sido objeto de grande interesse experimental nos últimos 10 anos. Usando a versão da nuvem que inclui o méson $\\kappa$, nós calculamos $G_E^s$ e $G_M^s$ em função do momento transferido dentro do intervalo 0 $\\leq Q^2 \\leq$ 1,2 GeV$^2$, de modo a abranger toda a gama de dados disponíveis no momento. Comparamos nossos resultados com os dados existentes para $G_E^s$ e $G_M^s$ e encontramos um ótimo acordo entre experimento e modelo, demonstrando que a inclusão do $\\kappa$ na núvem de mésons do próton é fundamental para que o seu conteúdo de estranheza possa ser compreendido. / The goal of this work was to include the scalar $\\kappa$ meson on the meson cloud of the proton, and then to verify if the strangeness contribution to the electromagnetic properties of the proton could be explained by the meson cloud model. The observables that quantify such a contribution are the electric ($G_E^s$) and magnetic ($G_M^s$) strange form factors, which have been subject of great experimental interest in the last 10 years. Using the version of the cloud which includes the $\\kappa$ meson, we calculated $G_E^s$ and $G_M^s$ as a function of the transferred momentum in the interval 0 $\\leq Q^2 \\leq$ 1.2 GeV$^2$, to cover the full range of available data at the time. We compared our results with existing data for $G_E^s$ and $G_M^s$ and we found a good agreement between experiment and model, showing that including $\\kappa$ on the meson cloud of the proton is crucial to understand its strangeness content.

O objetivo deste trabalho foi incluir o méson escalar $\\kappa$ na núvem de mésons estranhos do próton e verificar se, desta forma, a contribuição de estranheza para as suas propriedades eletromagnéticas poderia ser explicada pelo modelo da núvem mesônica. Os observáveis que quantificam tal contribuição são os fatores de forma estranhos elétrico ($G_E^s$) e magnético ($G_M^s$), que têm sido objeto de grande interesse experimental nos últimos 10 anos. Usando a versão da nuvem que inclui o méson $\\kappa$, nós calculamos $G_E^s$ e $G_M^s$ em função do momento transferido dentro do intervalo 0 $\\leq Q^2 \\leq$ 1,2 GeV$^2$, de modo a abranger toda a gama de dados disponíveis no momento. Comparamos nossos resultados com os dados existentes para $G_E^s$ e $G_M^s$ e encontramos um ótimo acordo entre experimento e modelo, demonstrando que a inclusão do $\\kappa$ na núvem de mésons do próton é fundamental para que o seu conteúdo de estranheza possa ser compreendido. / The goal of this work was to include the scalar $\\kappa$ meson on the meson cloud of the proton, and then to verify if the strangeness contribution to the electromagnetic properties of the proton could be explained by the meson cloud model. The observables that quantify such a contribution are the electric ($G_E^s$) and magnetic ($G_M^s$) strange form factors, which have been subject of great experimental interest in the last 10 years. Using the version of the cloud which includes the $\\kappa$ meson, we calculated $G_E^s$ and $G_M^s$ as a function of the transferred momentum in the interval 0 $\\leq Q^2 \\leq$ 1.2 GeV$^2$, to cover the full range of available data at the time. We compared our results with existing data for $G_E^s$ and $G_M^s$ and we found a good agreement between experiment and model, showing that including $\\kappa$ on the meson cloud of the proton is crucial to understand its strangeness content.