Experiments with polarized "ultracold neutrons" (UCN) offer a new way to measure the decay correlations of neutron beta decay; these correlations can be used to test the completeness of the Standard Model and predict physics beyond it. Ultracold neutrons are very low energy neutrons that can be trapped inside of material and magnetic bottles. The decay correlations in combination with the neutron and muon lifetimes experimentally find the first element (Vud) of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. The CKM matrix is a unitary transform between the mass and weak eigenstates of the d, s and b quarks; if the matrix is not unitary this would imply that the Standard Model is not complete. Currently the first row of the CKM matrix is over 2 sigma from unitarity and Vud is the largest component of the row. The UCNA experiment looks at the correlation between the polarization of the neutron and the momentum of the electron resulting from the beta decay of the neutron (the A-correlation). The keys to making a high precision measurement of A-correlation are a near 100% polarization of the neutrons that decay, low"backscatter electron detectors, and small, well characterized backgrounds. UCN can be 100% polarized by passing them through a seven Telsa magnetic field. The key to the UCNA experiment is keeping them polarized until they decay or are lost. This dissertation covers the development of guides that are minimally depolarizing and efficient transporters of UCN and their use in the UCNA experiment. The entire guide development process is covered from conception to manufacturing and testing. This process includes development of a pulsed laser deposition, diamond-like carbon coating system and materials studies of the resulting coatings. After the initial studies of the guide coating, meter"long sections of guide are tested with UCN to determine their depolarization and transport properties. The guide technology developed in this dissertation has been used in the entire UCNA experiment. Also, this technology is currently the state of the art for polarized and non-polarized UCN guide systems and it is being implemented in several new UCN experiments. / Ph. D.

Das Standardmodell der Teilchenphysik kann als die Niedrigenergielimit einer allgemeineren effektiven Feldtheorie des Standardmodells (SMEFT) betrachtet werden, die die Dynamik möglicher ultraviolette Vervollständigung in Form von höherdimensionalen Operatoren erfasst. Der zugehörige Parameterbereich ist groß und beinhaltet komplexe Mischungsmuster unter dem Renormierungsgruppenfluss (RG fluss). Dies erfordert eine gute Kontrolle über die Theorie und die Entwicklung effizienter Rechenwerkzeuge. In dieser Arbeit untersuchen wir allgemeiner effektive Feldtheorien. Wir haben dieses Vorhaben in zwei zentrale Themen unterteilt. Im ersten Teil untersuchen wir die Renormierung skalarer effektiver Feldtheorien auf Mehrschleifenordnung und bis zu hohen Massendimensionen. Neben der Generierung vieler neuer perturbativen Daten analysieren wir die wiederkehrenden Muster in der RG-Mischung und den Operatorenbasen, die diese aufzeigen. Die von uns entwickelten Werkzeuge und getroffenen Schlussfolgerungen lassen sich auch auf andere Theorien, wie die SMEFT, übertragen. Im zweiten Teil untersuchen wir die Erweiterung des Doppelkopierens (\emph{double copy}) auf effektive Feldtheorien auf Baum-Niveau. Das Doppelkopieren ist ursprünglich eine Beziehung zwischen den Amplituden der Yang--Mills-Theorie und der Gravitation und beruht auf einer nicht-trivialen Eigenschaft von Yang--Mills-Amplituden namens Farb-Kinematik-Dualität (\emph{color-kinematics duality}). Wir bewerten ihre Einschränkungen für höherdimensionale Operatoren und nutzen sie für die effiziente Erzeugung von Amplituden. Eines unserer Hauptergebnisse ist eine Reihe von Amplitudenrelationen, die höherdimensionale Korrekturen zur Yang--Mills-Theorie in Form von Bausteinen niedrigster Ordnung effizient codieren. / The Standard Model of particle physics can be seen as the low energy limit of a more general Standard Model effective field theory (SMEFT), which captures the dynamics of possible ultraviolet completions in terms of higher-dimensional operators. The associated parameter space is large and involves intricate mixing patterns under the renormalization group (RG) flow. This demands good control over the theory and the development of efficient computational tools. In this thesis we study effective field theories more generally. We have split this endeavor into two central themes. In Part I, we study the renormalization of scalar effective field theories at multi-loop order and up to high mass dimensions. Besides generating a lot of new perturbative data, we analyze the reoccurring patterns in the RG mixing and the operator bases that expose these. The tools we develop and conclusions we make extend to other theories, such as the SMEFT. In Part II, we study the extension of the double copy to effective field theories at tree level. The double copy is originally a relation between the amplitudes of Yang--Mills theory and gravity, and it relies on a non-trivial property of Yang--Mills amplitudes called the color-kinematics duality. We assess its restrictiveness for higher-dimensional operators, and we employ it for efficient amplitude generation. One of our main results is a set of amplitude relations which efficiently encode higher-derivative corrections to Yang--Mills theory in terms of lowest-order building blocks.

The Standard Model of particle physics attempts to unify the fundamental forces in the Universe (except gravity). Over the years it has been tested in numerous experiments. While these experimental results strengthen our understanding of the SM, they also point out directions for physics beyond the SM. In this thesis we assume supersymmetry (SUSY) to be the new physics beyond the SM. We have tried to analyze the present status of low energy SUSY after the recent results from direct (collider) and indirect (flavor, dark matter) searches .We have tried to see the complementarity between these apparently different experimental results and search strategies from the context of low energy SUSY. We show that such complementarity does exist in well-defined models of SUSY breaking like mSUGRA, NUHM etc. The first chapter outlines the present status of the SM and discusses about the unanswered questions in SM. Keeping SUSY as the new physics beyond the SM, we also detail about its present experimental status. Chapter1 ends with the motivation and comprehensive description about each chapter of the thesis. In chapter2, we present an introduction to formal structure of SUSY algebra and the structure of MSSM. One of the such complementarities we have studied is between flavor and dark matter. In general flavor violation effects are not considered when studying DM regions in minimal SUSY models like mSUGRA. If however flavor violation does get generated through non-minimal SUSY breaking sector, one of the most susceptible regions would be the co-annihilation region for neutralino DM. In chapter 3 we consider flavor violation in the sleptonic sector and study its implications on the stau co-annihilation region. In this work we have taken flavor violation between the right-handed smuon (˜µR) and stau (˜τR). Due to this flavor mixing the lightest slepton (ĺ1) is a flavor mixed state. We have studied the effect of such ĺ11’s in the ‘stau co-annihilation’ region of the parameter space, where the relic density of the neutralinos gets depleted due to efficient co-annihilation with the staus. Limits on the flavor violating insertion in the right-handed sleptonic sector mainly comes from BR(τ → µγ). These limits are weak in some regions of the Parameter space where cancellations happen with in the amplitudes. We look for overlaps in parameter space where both the co-annihilation condition as well as the cancellations with in the amplitudes occur. We have shown that in models with non-universal Higgs boundary conditions (NUHM) overlap between these two regions is possible. The effect of flavor violation is two fold: (a) It shifts the co-annihilation regions towards lighter neutralino masses and (b) the co-annihilation cross sections would be modified with the inclusion of flavor violating diagrams which can contribute significantly. In the overlap regions, the flavor violating cross sections become comparable and in some cases even dominant to the flavor conserving ones. A comparison among the different flavor conserving and flavor violating channels, which contribute to the neutralino annihilation cross-section, is presented. One of the challenges of addressing quantitatively the complementarity problems is the lack of proper spectrum generator (numerical tools which computes SUSY sparticle spectrum in the presence of flavor violation in the sfermionic sector). For the lack of a publicly available code which considers general flavor violating terms in the renormalization group equations (RGE) we have developed a SUSY spectrum calculator, named as SuSeFLAV .It is a code written in FORTRAN language and calculates SUSY particle spectrum (with in the context of gravity mediation) in type I seesaw, in the presence of heavy right handed neutrinos (RHN). SuSeFLAV also calculates the SUSY spectrum in other type of SUSY breaking mechanisms (e.g. gauge mediation). The renormalization group (RG) flow of soft-SUSY breaking terms will generate large off-diagonal terms in the slepton sector in the presence of this RHNs, which will give rise to sizable amount of flavor violating (LFV) decays at the weak scale. Hence, in this code we also calculate the different rare LFV decays like, µ → eγ, τ → µγ etc. In SuSeFLAV the user has the freedom to choose the scale of the RHNs as well as the mixing matrix in neutrino sector. It is also possible to choose the values of the SUSY breaking input parameters at the user defined scale. The details of this package is discussed in chapter 4. Many of the present studies of complementarity between the direct and indirect searches are inadequate to address realistic scenarios, where SUSY breaking could be much more general compared to the minimal models. The work in this thesis is a step to wards this direction. Having said that, in the present thesis we have considered modifications of popular models with either explicit flavor violating terms (in some sectors) or sources of flavor violation through new particles and new couplings motivated by strong phenomenological reasons like neutrino masses. It should be noted however, the numerical tool which has been developed during the thesis can be used to address more complicated problems like with complete flavor violation in models of SUSY breaking. One of the popular mechanisms of neutrino mass generation is the so called Seesaw Mechanism. Depending on the extra matter sector present in the theory there are three basic types of them. The type I seesaw, which has singlet bright-handed neutrinos, the type II seesaw contains scalar triplets and type III seesaw has additional fermionic triplets. One of the implications of the seesaw mechanism is flavor violation in the sfermionic sector even in the presence of flavor universal SUSY breaking. This leads to a complementarity between flavor experiments and direct SUSY searches at LHC. With the announcement of the results from the reactor neutrino oscillation experiments, the reactor mixing angle (θ13) in the neutrino mixing matrix (PMNS matrix) gets fixed to a rather large non-zero value. In SO (10) GUT theories neutrino Yukawa couplings of type I seesaw gets related to the up-type fermion sector of the SM. In chapter 5 we update the status of SUSY type I seesaw assuming SO (10)- like relations for neutrino Dirac Yukawa couplings and two cases of mixing, one large, PMNS-like, and another small, CKM-like, are considered. It is shown that for the large mixing case, only a small range of parameter space with moderate tan β is still allowed. It is shown that the renormalization group induced flavor violating slepton mass terms are highly sensitive to the Higgs boundary conditions. Depending on the choice of the parameters, they can either lead to strong enhancements or cancellations with in the flavor violating terms. We have shown that in NUHM scenario there could be possible cancellations which relaxes the severe constraints imposed by lepton flavor violation compared to mSUGRA. We further updated the flavor consequences for the type II seesaw in SUSY theories. As mentioned previously in type II seesaw neutrino mass gets generated due to exchange of heavy SU (2) L triplet Higgs field. The ratio of lepton flavor violating branching ratios (e.g. BR(τ → µγ) /BR (µ → eγ) etc.) are functions of low energy neutrino masses ans mixing angles. In chapter 6 we have analyzed how much these ratios become, after the experimental measurement of θ13, in the whole SUSY parameter space or in other words how much these ratios help to constrain the SUSY parameter space. We compute different factors which can affect this ratios. We have shown that the cMSSM-like scenarios, in which slepton masses are taken to be universal at the high scale, predict 3.5 BR(τ → µγ) / BR(µ → eγ) 30 for normal hierarchical neutrino masses. We Show that the current MEG limit puts severe constraints on the light sparticle spectrum in cMSSM-like model for seesaw scale with in1013 - 1015 GeV. These constraints can be relaxed and relatively light sparticle spectrum can be still allowed by MEG result in a class of models in which the soft mass of triplet scalar is taken to be non-universal at the GUT scale. In chapter 7 we have analyzed the effect of largen eutrino Yukawa couplings on the supersymmetric lightest Higgs mass. In July 2012, ATLAS and CMS collaboration have updated the Higgs search in LHC and found an evidence of a scalar particle having mass around 125 GeV. The one-loop contribution to Higgs mass mainly depends on the top trilinear couplings (At), the SUSY scale and the top Yukawa (Yt). Thus in models with extra large Yukawa couplings at the high scale like the seesaw mechanism ,the renormalization scaling of the At parameter can get significantly affected. This in turn can modify the light Higgs mass at the weak scale for the same set of SUSY parameters. We have shown in type I seesaw with (Yν ~ 3Yu) the light Higgs mass gets reduced by 2 - 3 GeV in most of the parameter rspace. In other words the SUSY scale must be pushed high enough to achieve similar Higgs mass compared to the cMSSM scenario. We have got similar effect in SUSY type III seesaw scenario with (Yν ~Yu) at the GUT scale. In chapter 8 we summarize the results of the thesis and discuss the possible future directions.

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In this doctoral thesis, we study both low- and high-energy observables related to massive neutrinos. Neutrino oscillations have provided indisputable evidence in favour of non-zero neutrino masses and mixings. However, the original formulation of the Standard Model cannot account for these observations, which calls for the introduction of new Physics. Among many possibilities, we focus here on the inverse seesaw, a neutrino mass generation mechanism in which the Standard Model is extended with fermionic gauge singlets. This model offers an attractive alternative to the usual seesaw realisations since it can potentially have natural Yukawa couplings (O(1)) while keeping the new Physics scale at energies within reach of the LHC. Among the many possible effects, this scenario can lead to deviations from lepton flavour universality. We have investigated these signatures and found that the ratios R_K and R_π provide new, additional constraints on the inverse seesaw. We have also considered the embedding of the inverse seesaw in supersymmetric models. This leads to increased rates for various lepton flavour violating processes, due to enhanced contributions from penguin diagrams mediated by the Higgs and Z bosons. Finally, we also found that the new invisible decay channels associated with the sterile neutrinos present in the supersymmetric inverse seesaw could significantly weaken the constraints on the mass and couplings of a light CP-odd Higgs boson.

Bakalauro baigiamajame darbe nagrinėjamos lanksčios darbo organizavimo formos bei jų taikymo galimybės. Tema analizuojama dviem aspektais: teoriniu ir praktiniu. Teorinėje dalyje aptarti pokyčiai darbo rinkoje, lanksčių darbo formų įvairovė, pateikti argumentai „už“ ir „prieš“ nestandartinių formų taikymą bei atlikta situacijos Lietuvoje analizė užimtumo aspektu. Praktinėje dalyje pateikiami trijų tikslinių grupių – dirbančių, nedirbančių bei studentų, tyrimo rezultatai. Nustatyta, kad nedirbantys asmenys sutiktų dirbti pagal lanksčias darbo organizavimo formas, o dirbantys nėra linkę keisti esamo darbo modelio. Studentai studijų metu pageidauja dirbti 4 valandas per dieną 5 dienas per savaitę. / Undergraduate thesis examined flexible forms of work organization and their application possibilities. Topic is analyzed in two aspects: theoretical and practical. In the theoretical part there are discussed changes in the labour market, flexible forms of employment diversity, the arguments for and against non-standard forms practise, and situation analysis of Lithuania. In the practical part there are proposed the examination results of three target groups - employed, unemployed and students. It was found that the unemployed are linked to accept work under flexible forms, and employed workers are reluctant to change the current working model. Analysed that students want to work 4 hours per day 5 days per week during the studies.