Browsing by Author "Ostrovskiy, Igor"

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    Experimental Search for Magnetic Monopoles via the Schwinger Effect At the LHC and Beyond
    (University of Alabama Libraries, 2024) Upreti, Aditya; Ostrovskiy, Igor
    Magnetic monopoles (MMs) naturally arise from Grand Unified Theories and are predicted by several beyond Standard Model (BSM) theories, some with masses detectable at the LHC. Previous collider searches, focused on elementary particle collisions, faced limitations that could have prevented MMs and complicated result interpretation. Most theoretical models predict MMs with internal structure, making their production in elementary particle collisions exponentially suppressed. Additionally, previous searches relied on tree-level diagrams to compute production rates, which are unreliable due to the MM's strong coupling. This thesis presents the first collider search for MMs that overcomes these limitations. The MoEDAL experiment at the LHC pioneered MM production searches in heavy-ion collisions via the Schwinger effect, which describes the generation of particle-antiparticle pairs in strong electromagnetic fields. Ultra-peripheral heavy-ion collisions at the LHC fleetingly generate the strongest magnetic fields known. The Schwinger cross section is calculable nonperturbatively, providing a reliable link between observed production rates and MM mass. The MM finite size enhances the production rate, allowing for the first reliable study of both elementary and composite monopoles at colliders. The author led the first MoEDAL analysis, published in Nature, which excluded MMs with 1 to 3 Dirac charges and masses up to 75 GeV/c^2 at 95% C.L., setting the first reliable limits on composite MMs. This thesis also extends the sensitivity to unprecedentedly high magnetic charges. The author led an analysis using data from the CMS beam pipe, donated to the MoEDAL collaboration. The beam pipe, exposed to heavy-ion collisions during LHC Run-1, was searched for MM signatures. This work, accepted to the Physical Review Letters, provides the strongest limits on MMs in the range of 2-45_gD and masses of up to 80 GeV/_c^2 at 95% C.L. Beyond collider searches, this thesis lays the groundwork for the next generation of MM searches in cosmic rays, which could either discover these elusive particles or refute the underlying theoretical models.
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    Magnetic Interactions and Transport in Periodically Driven Electronic Systems
    (University of Alabama Libraries, 2024) Ke, Modi; Tse, Wang-Kong
    The time-periodic driving field has traditionally been a standard tool for controlling small quantum systems, especially for atoms and molecules in laser fields. Its role in the solid state many-body systems has attracted increasingly more attention in recent years. This dissertation is focused on the study of magnetic interactions and transport in periodically driven electronic systems, leveraging the versatility of light to probe and control these phenomena. This thesis explores the non-equilibrium behaviors induced by external periodic driving fields and their effects on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions and interlayer tunneling current. The Keldysh-Floquet Green's function formalism together with the high frequency expansion is used to calculate the exchange interaction energy of two impurity lines on topological insulator surfaces. The first part of the thesis demonstrates how external driving fields can strongly influence the indirect exchange interaction by dynamically modifying the electronic band structure. In irradiated graphene, it is found that typical antiferromagnetic and ferromagnetic couplings in sublattices can be controlled by light. On the surface of a topological insulator, our findings show that an external driving field can be used to modify the spatial period of indirect exchange interactions between two parallel lines of magnetic impurities, including Heisenberg, Ising, and Dzyaloshinsky-Moriya(DM) interaction components of exchange interaction. Our work thus provides insights into how Floquet engineering can be used to control the indirect exchange interaction between magnetic impurities on graphene and the topological insulator surface. The second part of the thesis examines the tunneling charge and spin current in a double-layer heterostructure with the top layer's electron spins driven by a precessing magnetization due to exchange coupling to a microwave-driven magnetic layer under resonance. Calculations are conducted to demonstrate the dependence of charge and spin current on the precession angle, coupling strength, and driving frequency of the system. These results elucidate the spin pumping effects in van der Waals tunneling heterostructures and provide guidelines for further theoretical and experimental studies.
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    Measuring the neutrino mixing angle theta-13 with the double chooz far detector
    (University of Alabama Libraries, 2012) Ostrovskiy, Igor; Busenitz, Jerome K.; University of Alabama Tuscaloosa
    The neutrino mixing angle theta-13 is the last one which value is still unknown. This dissertation presents an analysis suggesting a non-zero value of the theta-13. The analysis is based on four months of data taken with the far Double Chooz reactor anti-neutrino detector. Using only rate information yields a best fit value of sin2(2theta-13) equal to 0.0934±0.0785 (1 sigma). Incorporating information on the shape of the signal energy spectrum in the analysis results in a best fit value of 0.0849±0.0509 (1 sigma). Based on frequentist studies, sin2(2theta-13)=0 is excluded at the 92.6% confidence level. The frequentist construction using delta chi-square as an ordering rule gives [0.0098, 0.1825] interval for sin2(2theta-13) at 90% C.L.