THREE ESSAYS ON MODEL SELECTION, MODULATION ESTIMATORS AND HERD BEHAVIOR UNDER ASYMMETRIC BELIEFS

This thesis is organized in three chapters. In the first two chapters, an econometric model selection procedure and a method to improve some existing estimators are proposed. In the third chapter, a theoretical microeconomic analysis of herd behavior is performed under a fairly new set of assumptions. In chapter one, a model selection procedure based on the Penalized Empirical Likelihood(PEL) technique is developed, and guidelines are provided for the extensionof the procedure to the setting of Generalized Empirical Likelihood (GEL). The procedurewas initially applied to linear models and was called "Least Absolute Shrinkage and Selection Operator" (LASSO). It was subsequently extended to Generalized Method of Moments models in, and we now extend it to Empirical Likelihood (EL)models. Its main advantage over classical methods is in the combination of model selection and model estimation into a single step, while improving the post-selection properties of the resulting estimators. This procedure is easy to implement, and it remains computationally feasible even in models with a large number of parameters. A simulation study is performed to compare the newly proposed procedure to someclassical methods such as AIC, BIC, and DT. The simulation results show a better performance of the new procedure. In chapter two, we define the modulation technique for the EL estimator modulation technique pertains to the class of methods generally known as "shrinkage methods".Shrinkage methods are frequently used to improve the properties, in particular smallsampleproperties, of existing estimators. In this paper, a general theoretical analysisof modulation estimators is developed for EL models, along with a discussion of howthey can be implemented in special cases.In chapter three, a theoretical model of imitation and herd behavior is considered.It is assumed in that some participating agents have specific abilities to affect otherpeoples behavior. Results are provided on how "stars" or celebrity players can impactherd formation. In the particular setting of a financial market with a single traded asset,results are provided on the consequences of this celebrity effect on bubble formationin the financial market

Weyl-Cartan-Weitzenb\"{o}ck gravity as a generalization of teleparallel gravity

We consider a gravitational model in a Weyl-Cartan space-time, in which the Weitzenb\"{o}ck condition of the vanishing of the sum of the curvature and torsion scalar is also imposed. Moreover, a kinetic term for the torsion is also included in the gravitational action. The field equations of the model are obtained from a Hilbert-Einstein type variational principle, and they lead to a complete description of the gravitational field in terms of two fields, the Weyl vector and the torsion, respectively, defined in a curved background. The cosmological applications of the model are investigated for a particular choice of the free parameters in which the torsion vector is proportional to the Weyl vector. Depending on the numerical values of the parameters of the cosmological model, a large variety of dynamic evolutions can be obtained, ranging from inflationary/accelerated expansions to non-inflationary behaviors. In particular we show that a de Sitter type late time evolution can be naturally obtained from the field equations of the model. Therefore the present model leads to the possibility of a purely geometrical description of the dark energy, in which the late time acceleration of the Universe is determined by the intrinsic geometry of the space-time.Comment: 15 pages, 5 figures; title changed, major modifications; accepted for publication in JCA

Brane worlds and dark matter

Two problems related to dark matter is considered in the context of a brane world model in which the confinement of gauge fields on the brane is achieved by invoking a confining potential. First, we show that the virial mass discrepancy can be addressed if the conserved geometrical term appearing in this model is considered as an energy momentum tensor of an unknown type of matter, the so-called X-matter whose equation of state is also obtained. Second, the galaxy rotation curves are explained by assuming an anisotropic energy momentum tensor for the X-matter.Comment: 13 pages, 1 figure, to appear in IJMP

INVESTIGATING AGE–BASED COMPLIMENTS IN PERSIAN

The present study was an attempt to investigate differences in the use of compliments in Persian across age as a social variable. Data was gathered through a Discourse Completion Task (DCT) with imaginary situations in which 200 native Persian speakers were asked to put themselves in those situations and give compliments. The results indicated that the most frequently used compliment strategies by Persian native speakers were explicit unbound semantic formula and non-compliment strategies. However, the participants used 'other' strategies, future reference, contrast, and request strategies the least. The results also suggested the effect of age on the distribution of compliments. While the younger participants preferred non-compliment strategies the most, the older participants preferred explicit unbound semantic formula strategies the most. However, despite minor differences, all age-groups rarely tended to use future reference, contrast, request, and 'other' strategies. The results cashed light on the cultural and socio-cultural factors affecting the way people offer compliments.Keywords: Pragmatic competence, Speech acts, Compliments, Discourse Completion Task (DCT), Social variable