Browsing by Subject "Supersymmetry"

Now showing 1 - 7 of 7
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    Beyond the Standard Model applications of holography
    (2020-07) Buyukdag, Yusuf
    In this thesis, we explore beyond the Standard Model of particle physics by taking advantage of the holography approach. First of all, we consider a supersymmetric model that uses partial compositeness to explain the fermion mass hierarchy and predict the sfermion mass spectrum. Linear mixing between elementary superfields and supersymmetric operators with large anomalous dimensions is responsible for simultaneously generating the fermion and sfermion mass hierarchies. After supersymmetry is broken by the strong dynamics, partial compositeness causes the first- and second-generation sfermions to be split from the much lighter gauginos and third-generation sfermions. The sfermion mass scale is constrained by the observed 125 GeV Higgs boson, leading to stop masses and gauginos around 10--100 TeV and the first two generation sfermion masses around 100--1000 TeV. This gives rise to a splitlike supersymmetric model that explains the fermion mass hierarchy while simultaneously predicting an inverted sfermion mass spectrum consistent with the Large Hadron Collider and flavor constraints. The lightest supersymmetric particle is a gravitino in the keV to TeV range, which can play the role of dark matter. This brings us to the second topic that we consider, a novel realization of the Dynamical Dark Matter (DDM) framework in which the ensemble of particles collectively constitute dark matter and they are the composite states of a strongly-coupled conformal field theory. Cosmological abundances for these states are then generated through mixing with an additional, elementary state. As a result, the physical fields of the DDM dark sector at low energies are partially composite. We calculate the masses, lifetimes, and abundances of these states --- along with the effective equation of state of the entire ensemble. Our results suggest the existence of a potentially rich cosmology associated with partially composite DDM.
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    Coupled quantum systems in inflationary cosmology.
    (2010-08) Gumrukcuoglu, Ahmet Emir
    The studies presented in this thesis describe applications of quantum field theory in a time dependent background. Two distinct problems are addressed in the framework of inflationary cosmology. The strict predictions of inflation are mostly in agreement with the Cosmic Microwave Background observations. In the recent years, large scale anomalies in the data motivated a series of analyses leading to a detection of broken statistical isotropy. Assuming that this effect is sourced by early time cosmology, I discuss the phenomenology of inflationary models extended to anisotropic backgrounds. Due to lack of rotational invariance, these models generically involve a system of coupled quantum fields. This leads to a tensor-scalar correlation function, which is a characteristic signature of these models. Another open question in cosmology involves the transition from inflation to the Hot Big Bang cosmology. In the presence of supersymmetric flat directions, the formation of the thermal radiation may undergo a dramatic delay, provided that these directions decay only perturbatively. In the scope of a toy model and a realistic example, both involving two flat directions, I discuss the nonperturbative decay that rapidly depletes the flat directions. If realized, this process can dramatically affect the previous assumptions on the thermalization scale. Due to the vast number of degrees of freedom, this problem generically involves coupled quantum fields. The decay of the flat directions gets contributions from both the diagonal (nonadiabatic evolution of frequency eigenvalues) and nondiagonal (nonadiabatic evolution of frequency eigenstates) effects. An additional characteristic effect of coupled quantization is the rotation of light eigenstates to heavy ones, which do not get produced in a diagonal system.
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    The evolution and decay of supersymmetric flat directions in the early universe and their role in thermalizing the universe
    (2008-12) Sexton, Matthew G.
    I study the post-inflation oscillation and decay of light coherent scalar field condensates that may develop during an inflationary phase of the universe. In particular, the light scalars studied are a composition of the scalar particles of a supersymmetric theory which correspond to the flat directions of the theory's scalar potential. Some toy models that possess supersymmetric flat directions are presented and numerical solutions for the evolution of the scalar fields are obtained. Both analytic and numeric results suggest that such condensates, if they existed in the early universe, can decay through a rapid and nonperturbative process long before these condensates could significantly affect the thermalization of the universe.
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    From heterotic supersymmetry to topological defects
    (2023-10) Kurianovych, Yevhen
    We study various applications of sigma models to heterotic supersymmetry and topological defects. We start with (0,1) minimal O(N) model where only left-moving fermions are present. Then we consider n connected copies of O(N) models in non-minimal model where both left-moving and right-moving fermions are present, but supersymmetry is broken for the right-movers. We study the non-minimal supersymmetric heterotically deformed (0, 2) sigma model with the Grassmannian target space. To develop the appropriate superfield formalism, we begin with a simplified model with flat target space, find its beta function up to two loops, and prove a non-renormalization theorem. Then we generalize the results to the full model with the Grassmannian target space. Using the geometric formulation, we calculate the beta functions and discuss the ’t Hooft and Veneziano limits. In the second part we study topological defects localized on other topological defects. We start with a simple model allowing the existence of domain walls with orientational moduli localized on them. We observe an O(3) sigma model on the wall world volume in the low-energy limit. We solve numerically classical static equations of motion and find the wall profile functions. We consider adding a spin-orbit interaction in the bulk, which gives rise to an entanglement between rotational and translational moduli, and calculate the corresponding low-energy Lagrangian. Within the O(3) sigma wall we obtain baby skyrmions localized on domain walls, and provide a solution for a skyrmion configuration, based on an analogy with instantons. We discuss the existence of one-dimensional domain walls localized on two-dimensional ones, and construct the corresponding effective action. We perform symmetry analysis of the initial model and of the low-energy theory on the domain wall world volume. In the end we give field-theoretic description of U(1) defects localized on the domain lines on thin films that were recently discovered experimentally. We describe topology of our model and solve this model in the adiabatic approximation. It turns out that such a model naturally provides periodic structure observed in experiment. The effective theory turns out to be the sine-Gordon model, but unlike the previous theoretical considerations we argue that in this case it is favorable for sine-Gordon kinks to merge into one defect with a uniform winding. We consider a system of adjacent domain lines and anti-lines and explain the experimental fact that the appearance of defects on a domain line prevents defect creation on the adjacent anti-lines. We also quantize the model and investigate possible effects of finite transverse dimension of the film.
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    No-Scale Inflation
    (2016-08) Garcia Garcia, Marcos
    Supersymmetry is the most natural framework for physics above the TeV scale, and the corresponding framework for early-Universe cosmology, including inflation, is supergravity. No-scale supergravity emerges from generic string compactifications and yields a non-negative potential, and is therefore a plausible framework for constructing models of inflation. No-scale inflation yields naturally predictions similar to those of the Starobinsky model based on $R + R^2$ gravity, with a tilted spectrum of scalar perturbations: $n_s∼0.96$, and small values of the tensor-to-scalar perturbation ratio $r < 0.1$, as favored by Planck and other data on the cosmic microwave background (CMB). In this thesis we introduce a novel no-scale inflationary model that averts the stabilization problem of supergravity models; to study it we develop a multi-field formalism applicable to supergravity models. We discuss the low-energy phenomenology of generic no-scale models and its connection to the lifetime of the inflaton. We use our results to analyze the constraints on these models imposed by CMB measurements, which through the calculation of the number of e-folds $N_*$ , we relate to constraints on the inflaton decay rate and other parameters of specific no-scale inflationary models. Finally, we revisit gravitino production following inflation, including thermal and non-thermal effects, and discuss the potential implications of upper limits on the gravitino abundance for no-scale models of inflation. Our results may provide insights into the embedding of inflation within string theory as well as its links to collider physics.
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    On extended supersymmetry in two and four dimensions.
    (2012-08) Koroteev, Peter A.
    We study the relationship between gauge theories in two and four dimensions with N = 2 supersymmetry. This includes the duality between their moduli spaces, comparison of Bogomolny-Prassad-Somerfield (BPS) spectra, study of instanton configurations, and other aspects. On they way we use various methods of integrability, conformal filed theories and string theory to achieve our goals. We start with describing physics of two dimensional N = 2 sigma models, geometry of their target spaces, their BPS spectra, and how they can de derived from four dimensional theories via BPS vortex construction. Two different approaches { gauge and geometric, as tools to study 2d theories, are compared in the light of perturbative as well as nonperturbative aspects of the theories in question. Then we discuss four dimensional supersymmetric gauge theories in presence of an Omega background { a special deformation used in localization of path integrals of supersymmetric theories. Instead of performing the localization we treat the Omega background physically and study BPS solitons for such theories, albeit the latter already possess less supersymmetry. Theories with N = 2 SUSY in Omega background are conjectured (and proven in special cases) to be dual to nonsupersymmetric conformal field theories in two dimensions by Alday, Gaiotto and Tachikawa (AGT duality). Employing the machinery of the 4d/2d duality combined with powerful methods of integrability we provide a proof of the AGT relation (in the limit where the 2d model in question exists). In the end we regard heterotic N = (0; 1) and N = (0; 2) sigma models in two dimensions. With fewer supersymmetry one has less control on the nonperturbative dynamics of the theory, however, we get some nice physical understanding of these models at strong coupling by means of the large number of colors approximation.
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    Topics in Two-dimensional Heterotic and Minimal Supersymmetric Sigma Models
    (2016-05) Chen, Jin
    Two-dimensional N=(0, 1) and (0, 2) supersymmetric sigma models can be mainly obtained in two ways: non-minimal heterotic deformation of N=(1, 1) and (2, 2) sigma models, and minimal construction which contains only (0, 1) and (0, 2) supermultiplets. The former deformed models with N=(0, 2) supersymmetries emerge as low-energy world sheet theories on non-Abelian strings supported in some N=1 four-dimensional Yang-Mills theories. The latter, on the other hand, can be regarded as the elementary building blocks to construct generic N=(0, 1) and (0, 2) chiral models. In the thesis, we will study both types of sigma models. We start with the deformed heterotic sigma models with N=(0, 2) supersymmetries. Our investigation is around the calculation of NSVZ exact beta-function of the heterotic models through instanton technique, and also verifies it by straightforward two-loop calculation and the ``Konishi anomaly'' of the hypercurrent. Finally, we also consider isometries on their target spaces, and show that the heterotic deformation is free of isometry and holonomy anomalies. Then we turn to analysis of a more fundamental minimal construction of chiral sigma models with N=(0, 1) and (0, 2) supersymmetries. These minimal models with only (left) chiral fermions may intrinsically suffer from chiral anomalies that will render the theories mathematically inconsistent. We focus on two important examples, the minimal O(N) and CP(N-1) models, and calculate their isometry anomalies. We show that the CP(N-1) models with N>2 has non-removable chiral anomalies, while the O(N) models are anomaly free and thus exist quantum mechanically. We also disclose a relation between isometry anomalies in these non-linear sigma models (NLSM) and gauge anomalies in gauged linear sigma models (GLSM). Finally, we reveal a relation on anomaly correspondence between NLSM and GLSM to minimal models on homogeneous spaces. We interpret these anomalies more from geometric perspectives and relate them to the characteristic classes of the target spaces. Through explicit calculation of anomalous fermionic effective action, we show how to add a series of local counterterms to remove the anomalies. We eventually reach a result that the remedy procedure is equivalent to require the target spaces of theories with trivial first Pontryagin class, and thus demonstrate Moore and Nelson's consistency condition in the case of homogeneous spaces. More importantly, we find that local counterterms further constrain ``curable'' models and make some of them flow to non-trivial infrared superconformal fixed point. We also discuss a interesting relation between N=(0, 1) and (0, 2) supersymmetric sigma model and gauge theories in the spirit of 't Hooft anomaly matching condition.