Search results for "Dark"
showing 10 items of 978 documents
Topics in Physics Beyond the Standard Model
2020
El Modelo Estándar (SM) de partículas es una teoría hermosa y extensamente contrastada. De hecho, sus éxitos son innumerables y algunas de sus predicciones, como el momento magnético anómalo de los electrones, se han confirmado con una precisión de una parte en 1010 (!). Sin embargo, y por suerte para mi doctorado, todavía hay preguntas abiertas que no se explican dentro del SM y requieren probablemente una dinámica subyacente o nueva física más allá del SM (BSM). Esta tesis explora, desde un punto de vista fenomenológico, algunas de las posibles extensiones del SM que permiten las preguntas abiertas en física fundamental: • El origen de las masas de los neutrinos • El origen de la asimetrí…
Dark Matter Phenomenology: Sterile Neutrino Portal and Gravitational Portal in Extra-Dimensions
2021
El Modelo Estándar de las Interacciones Fundamentales (SM) representa una de las teorías más precisas de la física. Entre las predicciones del SM encontramos, por ejemplo, el momento magnético anómalo del electrón a_e = 0,001159652181643 (764). Esta predicción coincide con los resultados experimentales en más de diez dígitos significativos, la predicción más precisa en la historia de la física. Sin embargo, hoy en día tenemos varias evidencias de que el SM solo explica el 5% del contenido de materia del Universo. El otro 95% está compuesto por las denominadas Energía Oscura y Materia Oscura. Como sugieren sus nombres, la naturaleza de estos dos componentes del contenido de energía / materia…
Composite scalars and dark matter from four-fermion interactions
2022
Parte I: Emergencia de masas en el Modelo Estándar El bosón de Higgs es un campo escalar del Modelo Estándar (SM, por sus siglas en inglés) de partı́culas elementales que cumple dos funciones muy importantes. Por un lado permite construir una teorı́a renormalizable. El potencial escalar contiene un término de masa y un término cuadrático en el campo de Higgs, los cuales son ajus- tados en base a mediciones experimentales y haciéndolos compatible con la aparición de una ruptura espontánea de la simetrı́a SU (2) L × U (1) Y del SM. Y por otra parte ayuda a explicar la masa de todos los fermiones en el esquema de la teorı́a cuántica de campos, al poseer interacciones de tipo Yukawa que son aju…
Search for a Stable Six-Quark State at BABAR
2019
Recent investigations have suggested that the six-quark combination uuddss could be a deeply bound state (S) that has eluded detection so far, and a potential dark matter candidate. We report the first search for a stable, doubly strange six-quark state in Upsilon -> S anti-Lambda anti-Lambda decays based on a sample of 90 million Upsilon(2S) and 110 million Upsilon(3S) decays collected by the BABAR experiment. No signal is observed, and 90% confidence level limits on the combined Upsilon(2S,3S) -> S anti-Lambda anti-Lambda branching fraction in the range (1.2-1.4)x10^-7 are derived for m_S < 2.05 GeV. These bounds set stringent limits on the existence of such exotic particles.
Polarization-Dependent Disappearance of a Resonance Signal -- Indication for Optical Pumping in a Storage Ring?
2021
We report on laser spectroscopic measurements on Li$^+$ ions in the experimental storage ring ESR at the GSI Helmholtz Centre for Heavy Ion Research. Driving the $2s\,^3\!{S}_1\;(F=\frac{3}{2}) \,\leftrightarrow\,2p\,^3\!P_2\;(F=\frac{5}{2}) \leftrightarrow 2s\,^3\!{S}_1\;(F=\frac{5}{2})$ $\Lambda$-transition in $^7$Li$^+$ with two superimposed laser beams it was found that the use of circularly polarized light leads to a disappearance of the resonance structure in the fluorescence signal. This can be explained by optical pumping into a dark state of polarized ions. We present a detailed theoretical analysis of this process that supports the interpretation of optical pumping and demonstrate…
The pineal complex in Roman high avoidance and Roman low avoidance rats.
1990
Previous studies have shown that the pineal gland of Roman high avoidance (RHA/Verh) rats is larger than that of Roman low avoidance rats (RLA/Verh). In the present study measurement of enzyme activities (serotonin-N-acetyl-transferase, hydroxyindole-O-methyltransferase) revealed that pineals of RHA/Verh rats are twice as active in melatonin production than pineals of RLA/Verh rats. Indoleamine content was also higher in RHA/Verh rats, whereas noradrenaline content was the same in both lines. When values were expressed per mg protein, these differences disappeared except for N-acetyl-serotonin and noradrenaline which were higher or lower in RHA/Verh rats, respectively. Both lines had higher…
Response of pineal serotonin N-acetyltransferase activity in male guinea pigs exposed to light pulses at night.
1988
Serotonin N-acetyltransferase (NAT), which is crucial for the formation of melatonin, undergoes a typical day/night rhythm in the pineal gland with low levels during daytime and high levels at night. Short pulses of light given at night have been shown to rapidly depress NAT activity in some species, but not in others, the reasons for this difference being unclear. As diurnality and nocturnality of the experimental animals may play a role and since diurnally active animals have been little investigated in this respect, in the present study the diurnally active guinea pig was investigated. Male guinea pigs kept under a lighting regimen of LD 12:12 (lights off at 1700 hrs) were killed between…
Some physiological and psychological characteristics of myopic and non-myopic young men.
2009
As a part of a research project on the health and functional capacity of men at different ages a comparison of selected physiological and psychological characteristics of myopic and non-myopic 31–35 year-old men was made. The random sample studied consisted of 31 myopic and 100 non-myopic men. It was found that the body mass index and fat content were lower among the myopic than among the non-myopic. No significant differences were found in the elastic properties of skin, in blood pressure or in haematological assays studied between the groups. With respect to physical performance it was observed that the myopic had a higher aerobic capacity whereas there were no significant differences in …
Methodological Aspects of the Application of the Naka-Rushton Equation to Clinical Electroretinogram
1993
The nonlinear relation between stimulus intensity and response amplitude of the electroretinogram (ERG) scotopic b wave can be described by a curve based on the Naka-Rushton (NR) equation. Up to now, the NR equation has been used to assess the features of the normal and pathological ERG, but the best approach for a correct evaluation of the parameters is still debatable. The parameters are thought to be related to the different conditions of retinal activities. The method is well known in experimental laboratories but is quite unusual at the clinical level. In the present paper the derivative analysis of the NR function is proposed as an easier approach to understand the variations of the N…
Asymmetric modulation of human visual cortex activity during 10 degrees lateral gaze (fMRI study).
2005
We used BOLD fMRI to study the differential effects of the direction of gaze on the visual and the ocular motor systems. Fixation of a target straight ahead was compared to fixation of a target 10 degrees to the right and 10 degrees to the left from gaze straight ahead, and to eyes open in complete darkness in thirteen healthy volunteers. While retinotopic coordinates remained the same in all fixation conditions, the fixation target shifted with respect to a head-centered frame of reference. During lateral fixation, deactivations in higher-order visual areas (one ventral cluster in the lingual and fusiform gyri and one dorsal cluster in the postero-superior cuneus) and, as a trend, activati…