RESUMEN La primera parte de la tesis está relacionada con modelos con dimensiones extra universales (todas las partículas se propagan en la dimensión extra). En estos modelos, a bajas energías, los primeros efectos aparecen al nivel de un loop. Como consecuencia, nuevas partículas relacionadas con las dimensiones extra pueden ser relativamente ligeras. En esta parte se analiza quan ligeras pueden ser y si pueden ser producidas en las actuales o inmediatamente futuras instalaciones experimentales. La tesis estudia las contribuciones a la desintegración del Z en quarks b, la cual muestra una fuerte dependencia con la masa del top y experimentalmente está bien medida . Este proceso proporciona el mejor límite en la masa de las nuevas partículas, junto con el obtenido del parámetro rho. De todos modos, solo es 300 GeV (95 % CL), lo que hace accesibles las nuevas partículas a las futuras instalaciones experimentales. En la segunda parte, se estudian las correcciones a las constantes gauge en forma de potencias en modelos con dimensiones extra. Lo cual es muy importante porque si estas correcciones pudiesen ser controladas podría ser posible comprobar modelos de Gran Unificación a bajas energías. Usando teorías efectivas, se concluye en la tesis que estas correcciones pueden ser calculadas sin ambigüedad solo cuando se conoce, aunque sea parcialmente, la teoría más completa que genera la teoría extra dimensional. Finalmente la tesis presenta las versiones latizadas de dos modelos diferentes con dimensiones extra y estudia su fenomenología. ____________________________________________________________________________________________________

This thesis can be framed into a more extense research project aimed to provide a practical post-graduate training that makes up for the lack of training in Clinical Psychology, at that moment. To that purpose, the Service of Psychological Assistance of the Personality, Assessment and Psychological treatment department of the University of Valencia is created. The sample for my study of different anxiety disorders was taken from this service. The main purpose was to refine a test, the R-3, that could discriminate aspects of rigidity between normal population and those people with any kind of anxiety disorder. To that purpose, this scale was applied to both normal population and population suffering from any anxiety disorder according to DSM-III-R, in four different phases: pre-test, post-test, and two follow-ups. The population with anxiety disorders was treated with different kinds of therapy that were never related to rigidity. Thus, this population was assessed before the treatment (pre-test), after the treatment during the 9th or 16th week (post-test) and during the two subsequent follow-ups a month and a half and three months later. Once the test had been refined, several psychometric analysis were performed with it. Among the main conclusions we find out that: 1. The personality variable rigidity has two sides: a positive and a negative one. 2. From the psychometric analysis carried out using the abbreviated scale, we can stand out the temporal stability of the scale. Consequently, rigidity measured with the abbreviated scale seems to be a stable dimension that is found in a prime level of personality, and therefore, difficult to modify. 3. Last, as concerns sensibility to change of the scale, important differences can be found when we compare rigidity before and after therapy. However, such difference is not found in any of the two follow-ups.