Browsing by Author "Chang, Lay Nam"
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- Bell's Inequalities, Superquantum Correlations, and String TheoryChang, Lay Nam; Lewis, Zachary; Minic, Djordje; Takeuchi, Tatsu; Tze, Chia-Hsiung (Hindawi, 2011-01-01)We offer an interpretation of super-quantum correlations in terms of a “doubly” quantum theory. We argue that string theory, viewed as a quantum theory with two deformation parameters, the string tension a′ and the string coupling constant gs, is such a super-quantum theory, one that transgresses the usual quantum violations of Bell’s inequalities. We also discuss the ħ ⟶ ∞ limit of quantum mechanics in this context. As a super-quantum theory, string theory should display distinct experimentally observable super-correlations of entangled stringy states.
- Bell's Inequalities, Superquantum Correlations, and String TheoryChang, Lay Nam; Lewis, Zachary; Minic, Djordje; Takeuchi, Tatsu; Tze, Chia-Hsiung (Hindawi Publishing Corporation, 2011)We offer an interpretation of superquantum correlations in terms of a “doubly” quantum theory.We argue that string theory, viewed as a quantum theory with two deformation parameters, the string tension α', and the string coupling constant gs, is such a superquantum theory that transgresses the usual quantum violations of Bell's inequalities. We also discuss the ℏ→∞ limit of quantum mechanics in this context. As a superquantum theory, string theory should display distinct experimentally observable supercorrelations of entangled stringy states.
- Bhabha scattering in e⁺e⁻ collisions at TRISTANLai, Anzhi (Virginia Tech, 1992-05-05)Bhabha scattering, the process of e⁺e⁻ → e⁺e⁻, has been studied at center-of-mass energies from 50 to 58 GeV with the AMY detector at the KEK e⁺e⁻ storage ring TRISTAN. The study is based on a data sample of 79.7 pb⁻¹ integrated luminosity. The differential cross section of Bhabha scattering has been measured. The measured cross section is found to agree fairly well with the Standard Model of the electroweak theory. The measured cross section is also compared with various four-fermion contact interaction models, and confidence level lower limits on the composite scale, A, are determined. In addition, the limits on VV model are converted to SM-break-down scales, which indicate the validity of the SM down to the distance of order ~ 10⁻¹⁷ cm and the electron charge radius of ~ 10⁻¹⁶ cm. Attempts are made in searching for an additional boson Z'. No clear signal of the existence of a Z' boson is found up to energy of ~160 GeV/c². The effect of transverse beam polarization on Bhabha scattering is also studied. The ϕ dependence of Bhabha events are fitted to the QED prediction and found to agree with the theory. However, no quantitative conclusion on polarization effect can be drawn based on current data sample, which does not provide enough statistics. More data is being accumulated and further study should be carried out.
- Biorthogonal quantum mechanics: super-quantum correlations and expectation values without definite probabilitiesChang, Lay Nam; Lewis, Zachary; Minic, Djordje; Takeuchi, Tatsu (IOP, 2013-12-06)We propose mutant versions of quantum mechanics constructed on vector spaces over the finite Galois fields GF(3) and GF(9). The mutation we consider here is distinct from what we proposed in previous papers on Galois field quantum mechanics. In this new mutation, the canonical expression for expectation values is retained instead of that for probabilities. In fact, probabilities are indeterminate. Furthermore, it is shown that the mutant quantum mechanics over the finite field GF(9) exhibits super-quantum correlations (i.e. the Bell-Clauser-Horne-Shimony-Holt bound is 4). We comment on the fundamental physical importance of these results in the context of quantum gravity.
- Classical and quantum gravity with Ashtekar variablesSoo, Chopin (Virginia Tech, 1992)This thesis is a study of classical and quantum gravity with Ashtekar variables. The Ashtekar constraints are shown to capture the essence of the constraints and constraint algebra of General Relativity in four dimensions. A classification scheme of the solution space of the Ashtekar constraints is proposed and the corresponding physics is investigated. The manifestly covariant equations of motion for the Ashtekar variables are derived. Explicit examples are discussed and new classical solutions of General Relativity are constructed by exploiting the properties of the Ashtekar variables. Non-perturbative canonical quantization of the theory is performed. The ordering of the quantum constraints as well as the formal closure of the quantum constraint algebra are explored. A detailed Becchi-Rouet-Stora-Tyutin (BRST) analysis of the theory is given. The results demonstrate explicitly that in quantum gravity, fluctuations in topology can occur and there are strong evidences of phases in the theory. There is a phase which is described by a topological quantum field theory (TQFT) of the Donaldson-Witten type and an Abelian antiinstanton phase wherein self-interactions of the gravitational fields produce symmetry breaking from SO(3) to U(1). The full theory is much richer and includes fluctuations which bring the system out of the various restricted sectors while preserving diffeomorphism invariance. Invariants of the quantum theory with are constructed through BRST descents. They provide a clear and systematic characterization of non-local observables in quantum gravity, and can yield further differential invariants of four-manifolds.
- Classical Implications of the Minimal Length Uncertainty RelationBenczik, S. Z.; Chang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Rayyan, S.; Takeuchi, Tatsu (2002-09-12)We study the phenomenological implications of the classical limit of the "stringy" commutation relations [x_i,p_j]=i hbar[(1+beta p^2) delta_{ij} + beta' p_i p_j]. In particular, we investigate the "deformation" of Kepler's third law and apply our result to the rotation curves of gas and stars in spiral galaxies.
- College of Science Annual Report 2005-2006Chang, Lay Nam (College of Science, 2006)
- College of Science Annual Report 2006-2007Chang, Lay Nam (College of Science, 2007)
- College of Science Annual Report 2007-2008Chang, Lay Nam (College of Science, 2008)
- College of Science Annual Report 2008-2009Chang, Lay Nam (College of Science, 2009)
- College of Science Annual Report 2009-2010Chang, Lay Nam (College of Science, 2010)
- Composite models of quarks and leptonsGeng, Chaqiang (Virginia Polytechnic Institute and State University, 1987)We review the various constraints on composite models of quarks and leptons. Some dynamical mechanisms for chiral symmetry breaking in chiral preon models are discussed. We have constructed several "realistic candidate" chiral preon models satisfying complementarity between the Higgs and confining phases. The models predict three to four generations of ordinary quarks and leptons.
- Constraints on gauged B-3L(tau) and related theoriesChang, Lay Nam; Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2001-04-01)
- Constraints on gauged B-3L(tau) and related theoriesChang, Lay Nam; Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2001-04-01)We consider extensions of the standard model with an extra U(1) gauge boson that couples to B- (alphaL(e), + betaL(mu) + gammaL(tau)) with alpha + beta + gamma =3. We show that the extra gauge boson necessarily mixes with the Z, leading to potentially significant corrections to the Zf(f) over bar vertex. The constraints on the size of this correction imposed by the Z-pole data from CERN LEP and SLD are derived.
- Correlations in the one-dimensional Hubbard modelQue, Wei-ming (Virginia Polytechnic Institute and State University, 1986)Correlation effects in the one-dimensional Hubbard model are studied by application of the L-resolvent method. The calculations are well beyond one-particle mean field approximation. All correlations involving two neighboring sites are included exactly and higher order correlations are approximated. The effects of varying temperature, band filling, Coulomb repulsion and external magnetic field are investigated. Two-site correlations for non-half-filled band fillings are calculated for the first time. Some exact relations between correlation functions are derived by electron-hole symmetry. Results indicate that short-range spin correlations always favor antiferromagnetic order. Large Coulomb repulsion induces a gap in the excitation spectrum and a metal-insulator transition is predicted as the Coulomb repulsion parameter is changed.
- Effect of the minimal length uncertainty relation on the density of states and the cosmological constant problemChang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Takeuchi, Tatsu (American Physical Society, 2002-06-15)We investigate the effect of the minimal length uncertainty relation, motivated by perturbative string theory, on the density of states in momentum space. The relation is implemented through the modified commutation relation [(x) over cap (i),(p) over cap (j)]=i (h) over bar[(1+beta(p) over cap (2))delta(ij)+beta(')(p) over cap (i)(p) over cap (j)]. We point out that this relation, which is an example of a UV/IR relation, implies the finiteness of the cosmological constant. While our result does not solve the cosmological constant problem, it does shed new light on the relation between this outstanding problem and UV/IR correspondence. We also point out that the blackbody radiation spectrum will be modified at higher frequencies, but the effect is too small to be observed in the cosmic microwave background spectrum.
- Effect of the minimal length uncertainty relation on the density of states and the cosmological constant problemChang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Takeuchi, Tatsu (American Physical Society, 2002-06-15)
- Effects of gravity on equilibrium crystal shapesGittis, Apostolos Georgios (Virginia Polytechnic Institute and State University, 1988)The effects of gravity on the two-dimensional equilibrium shapes (ES) of crystals and menisci are investigated for different geometries (positions) of the substrate. In the gravity-free case, the equilibrium crystal shape (ECS) is characterized by a scale invariance. The presence of gravity breaks the scale invariance and the resulting ECS changes as the volume of the crystal V is changed. Moreover, the presence of gravity breaks the translational invariance along the direction it acts. Physically realized by the necessity of a support, this is manifested by the existence of an inhomogeneous effective pressure Peff, which divides the space into two regions, with Peff either negative or positive. The ECS changes as the crystal passes from one region to another, being concave where Peff < 0, and convex where Peff > 0. In all cases it was possible to express the corresponding ECS in terms of the gravity-free one. For the hung crystal, i.e., a crystal pinned to a vertical wall at the top, it is shown that some orientations are missing from the ECS that otherwise will be present in the gravity-free ECS, adsorbed on the same substrate. Thus, facets could disappear from the crystal shape as the volume V or the gravitational acceleration g is increased. A critical volume Vc is found, so that if the crystal volume V exceeds Vc, the crystal cannot be pinned. The ECS can exhibit both concave and convex portions. For a crystal, pinned to a vertical wall at its lower end, we find that it will never develop a concave part. On the other hand, new orientations, absent from the gravity-free crystal, will be present on its ECS. The ES of a free and pinned crystal meniscus is also solved and an expression for the excess (depleted) volume AV is derived. The solution for the crystal meniscus between two walls is also presented. For the pendant crystal, i.e., a crystal hanging from a horizontal support, we find that it can exhibit both concave and convex portions on its ECS. When it develops a concave part, new orientations will appear, compared to the gravity-free case. An intuitive stability criterion is introduced, according to which only crystals wetting the substrate can develop a concave portion before they break. The treatment of a crystal on an inclined substrate shows the complications that arise in determining the ES for a general position of the support as a result of the conflict between the directions associated with gravity and support. An expression for the facet length in the presence of gravity is obtained that is valid for all types of support. For crystal shapes that display a concave portion it offers a very convenient way to experimentally measure step free energies. Thus, by breaking scale invariance, the presence of gravity allows absolute measures of surface energy in contrast to the gravity-free case, where the facet length is proportional to the step free energy by an unknown scale.
- Electrical, Thermal, and EMI Designs of High-Density, Low-Profile Power SuppliesZhang, Michael Tao (Virginia Tech, 1998-02-17)This work presents the analyses and designs of high-density, low-profile power supplies, including the electrical, thermal, and EMI aspects. Emphasis is placed on forward and flyback converters. The efficiency improvements of employing synchronous rectification are theoretically derived and experimentally verified in forward and flyback converters. The performances of synchronous rectifiers in forward converters are analyzed with regards to transformer reset and SR driven method. The effectiveness of synchronous rectification in flyback converters is evaluated in various operation modes and control schemes. The paralleling techniques utilized to realize high-density, low-profile power conversion are presented. Current sharing in transformer paralleling is addressed and evaluated in forward topology. The performance and the operation principles of one-choke and two-choke interleaved forward converters are analyzed. The thermal management of high-density power supplies in sealed enclosures is optimized using computational fluid dynamics simulations. The theoretical limit of power density due to thermal constraint is determined. In addition, the thermal-design optimization guidelines are given and verified experimentally. A systematic methodology is developed to facilitate the analysis and design of conducted EMI problems in high-density power supplies. Partial element equivalent circuit method is employed for parasitic parameter extraction. Layout and packaging are optimized to minimize conducted EMI noises. Noise predictions by Saber simulations are confirmed by experimental measurements.
- Electron-positron annihilation into photons at √s = 50 to 64 GeVSterner, Kevin L. (Virginia Tech, 1993)We present a study of e⁺e⁻ collisions where only photons are visible in the final state in data taken with the AMY detector at TRISTAN. Data are presented at CM energies from 50 to 64 GeV, with a total integrated luminosity of 189.1 pb⁻¹. Differential cross sections for e⁺e⁻ → γγ, γγγ are measured and compared to 𝛰(α³) QED. A search for electron compositeness through an e⁺e⁻ γγ contact interaction is conducted, and limits are presented. A search for the pair production of unstable photinos is also presented with limits. Finally, the result of a search for anomalous γγ production is presented, based upon energy scan data taken in December, 1992.