SUSY breaking in $S^1/Z_2$ orbifold models
We consider the problem of supersymmetry breaking in 5 dimensional N=1 supersymmetric models with $S^1/Z_2$ compactification.
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arXiv subjects
M. Chaichian
Publications and source records attributed to M. Chaichian.
Renormalization Constant of the Color Gauge Field as a Probe of Confinement
The mechanism of color confinement as a consequence of an unbroken non-abelian gauge symmetry and asymptotic freedom is elucidated and compared with that of other models based on an analogy with the type II superconductor. It is demonstrated that a sufficient condition for color confinement is given by $Z_3^{-1}=0$ where $Z_3$ denotes the renormalization constant of the color gauge field. It is shown that this condition is actually satisfied in quantum chromodynamics and that some of the characteristic features of other models follow from it.
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Single sneutrino production in $γγ$ collisions
We study the single production of sneutrinos with two leptons (or jets) via $γγ$ collision in an R-parity ($R_{p}$) violating supersymmetric model. The subsequent decays of the sneutrino are also considered. The single production of sneutrinos may provide a significant test of supersymmetry and $R_p$-violation with flavour conserving and flavour changing final states. If such processes coming from $R_p$ violation are not detected, the parameter space of the model will be strongly constrained at the future Linear Collider.
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Composite quarks and leptons in higher space-time dimensions
A new approach towards the composite structure of quarks and leptons in the context of the higher dimensional unified theories is proposed. Owing to the certain strong dynamics, much like an ordinary QCD, every possible vectorlike multiplets of composites appear in higher dimensional bulk space-time, however, through a proper Sherk-Schwarz compactification only chiral set of composite quarks and leptons survive as the massless states in four dimensions. In this scenario restrictions related with the 't Hooft's anomaly matching condition are turned out to be avoided and, as a result, the composite models look rather simple and economic. We demonstrate our approach by an explicit construction of model of preons and their composites unified in the supersymmetric SU(5) GUT in five space-time dimensions. The model predicts exactly three families of the composite quarks and leptons being the triplets of the chiral horizontal symmetry SU(3)_h which automatically appears in the composite spectrum when going to ordinary four dimensions.
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Vanishing of cosmological constant and fully localized gravity in a Brane World with extra time(s)
We construct an intersecting brane configuration in six-dimensional space with one extra space-like and one extra time-like dimensions. With a certain additional symmetry imposed on the extra space-time we have found that effective four-dimensional cosmological constant vanishes automatically, providing the static solution with gravity fully localized at the intersection region as there are no propagating massive modes of graviton. In this way, the same symmetry allows us to eliminate tachyonic states of graviton from the spectrum of the effective four-dimensional theory, thus avoiding phenomenological difficulties comming from the matter instability usually induced in theories with extra time-like dimensions.
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Quantum Theories on Noncommutative Spaces with Nontrivial Topology: Aharonov-Bohm and Casimir Effects
After discussing the peculiarities of quantum systems on noncommutative (NC) spaces with non-trivial topology and the operator representation of the $\star$-product on them, we consider the Aharonov-Bohm and Casimir effects for such spaces. For the case of the Aharonov-Bohm effect, we have obtained an explicit expression for the shift of the phase, which is gauge invariant in the NC sense. The Casimir energy of a field theory on a NC cylinder is divergent, while it becomes finite on a torus, when the dimensionless parameter of noncommutativity is a rational number. The latter corresponds to a well-defined physical picture. Certain distinctions from other treatments based on a different way of taking the noncommutativity into account are also discussed.
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Noncommutative Gauge Field Theories: A No-Go Theorem
Studying the general structure of the noncommutative (NC) local groups, we prove a no-go theorem for NC gauge theories. According to this theorem, the closure condition of the gauge algebra implies that: 1) the local NC $u(n)$ {\it algebra} only admits the irreducible n by n matrix-representation. Hence the gauge fields are in n by n matrix form, while the matter fields {\it can only be} in fundamental, adjoint or singlet states; 2) for any gauge group consisting of several simple-group factors, the matter fields can transform nontrivially under {\it at most two} NC group factors. In other words, the matter fields cannot carry more than two NC gauge group charges. This no-go theorem imposes strong restrictions on the NC version of the Standard Model and in resolving the standing problem of charge quantization in noncommutative QED.
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Radions in a $γγ$ collider
We study the resonance production of radions via $γγ$ fusion in the Randall-Sundrum model. We find that the cross section of the process in the $γγ$ mode of a linear collider (LC) can be of similar size as in the $e^+e^-$ collision mode, if the radion is heavy. We consider the possible curvature-Higgs mixing in the model, and we find that the mixing should be constrained in order to avoid an unphysical state. The process $γγ\to ϕ$ is the main source of radions at LC near the conformal limit. We consider both the decay modes of radion with curvature-Higgs mixing and without. Our results show that the radion with mass below 800 GeV could be detected at LC with any mixing parameter and vacuum expectation value of the radion around 1 TeV.
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Aharonov-Bohm Effect in Noncommutative Spaces
The Aharonov-Bohm effect on the noncommutative plane is considered. Developing the path integral formulation of quantum mechanics, we find the propagation amplitude for a particle in a noncommutative space. We show that the corresponding shift in the phase of the particle propagator due to the magnetic field of a thin solenoid receives certain gauge invariant corrections because of the noncommutativity. Evaluating the numerical value for this correction, an upper bound for the noncommutativity parameter is obtained.
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Single superparticle production via $γγ$ collision with explicit R-parity violation
We study the single production of scalar neutrinos or charginos via $γγ$ collision in an R-parity ($R_{p}$) violating supersymmetric model. It may be possible to detect a sneutrino or a chargino at a Linear Collider (LC) in $γγ$ operation mode, as a test of supersymmetry and $R_p$-violation. Because of the clean background in LC, stringent constraints on $R_p$ violating parameters can be obtained even if the process cannot be observed at the future Linear Collider.
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Radiatively Induced Lorentz and CPT Violation in Schwinger Constant Field Approximation
The Schwinger proper-time method is an effective calculation method, explicitly gauge invariant and nonperturbative. We make use of this method to investigate the radiatively induced Lorentz and CPT-violating effects in quantum electrodynamics when an axial vector interaction term is introduced in the fermionic sector. The induced Lorentz and CPT-violating Chern-Simons term coincides with the one obtained using a covariant derivative expansion but differs from the result usually obtained in other regularization schemes. A possible ambiguity in the approach is also discussed.
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Hydrogen Atom Spectrum and the Lamb Shift in Noncommutative QED
We have calculated the energy levels of the hydrogen atom and as well the Lamb shift within the noncommutative quantum electrodynamics theory. The results show deviations from the usual QED both on the classical and on the quantum levels. On both levels, the deviations depend on the parameter of space/space noncommutativity.
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New Superconformal Field Theories in Four Dimensions and N=1 Duality
Recently, developments in the understanding of low-energy N=1 supersymmetric gauge theory have revealed two important phenomena: the appearance of new four-dimensional superconformal field theories and a non-Abelian generalization of electric-magnetic duality at the IR fixed point. This report is a pedagogical introduction to these phenomena. After presenting some necessary background material, a detailed introduction to the low-energy non-perturbative dynamics of N=1 supersymmetric $SU(N_c)$ QCD is given. The emergence of new four-dimensional superconformal field theories and non-Abelian duality is explained. New non-perturbative phenomena in supersymmetric $SO(N_c)$ and $Sp(N_c=2n_c)$ gauge theories, such as the two inequivalent branches, oblique confinement and electric-magnetic-dyonic triality, are presented. Finally, some new features of these four-dimensional superconformal field theories are exhibited: the universal operator product expansion, evidence for a possible $c$-theorem in four dimensions and the critical behaviour of anomalous currents. The concluding remarks contain a brief history of electric-magnetic duality and a discussion on the possible applications of duality to ordinary QCD.
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R-parity violation in $(t+\bar t)\tilde g$ production at LHC and Tevatron
We study the production of $(t+\bar{t}) \tilde{g}$ at the hadron colliders in an R-parity ($R_{p}$) violating supersymmetric model. This process provides us with information not only about $R_{p}$ violation, but may also help us in detecting the supersymmetry itself. It is possible to detect an $R_{p}$ violating signal (with single gluino production) at the future hadron colliders, such as Fermilab Tevatron Run II or CERN Large Hadron Collider (LHC), if the parameters in the supersymmetric $\rlap/ R_{p}$ interactions are not too small, e.g. for $m_{\tilde{g}}=1$ TeV, $λ^{''}=0.1$, still hundreds of events are produced at LHC with luminosity $30 fb^{-1}$. Even if we could not detect a signal of $ \rlap/R_{p}$ in the experiment, we get stringent constraints on the heavy flavour $\rlap/R_{p}$ couplings. In addition to the minimal supersymmetric standard model we have also considered some models with a heavy gluino as the lightest supersymmetric particle.
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Space-Time Noncommutativity, Discreteness of Time and Unitarity
Violation of unitarity for noncommutative field theory on compact space-times is considered. Although such theories are free of ultraviolet divergences, they still violate unitarity while in a usual field theory such a violation occurs when the theory is nonrenormalizable. The compactness of space-like coordinates implies discreteness of the time variable which leads to appearance of unphysical modes and violation of unitarity even in the absence of a star-product in the interaction terms. Thus, this conclusion holds also for other quantum field theories with discrete time. Violation of causality, among others, occurs also as the nonvanishing of the commutation relations between observables at space-like distances with a typical scale of noncommutativity. While this feature allows for a possible violation of the spin-statistics theorem, such a violation does not rescue the situation but makes the scale of causality violation as the inverse of the mass appearing in the considered model, i.e., even more severe. We also stress the role of smearing over the noncommutative coordinates entering the field operator symbols.
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High-dimensional sources for the four-dimensional gravity
We argue that a certain distribution of matter in higher dimensions can provide the correct behaviour of gravity in four dimensions. Some explicit examples illustrating the idea are considered.
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Field Theory on Noncommutative Space-Time and the Deformed Virasoro Algebra
We consider a field theoretical model on the noncommutative cylinder which leads to a discrete-time evolution. Its Euclidean version is shown to be equivalent to a model on the complex $q$-plane. We reveal a direct link between the model on a noncommutative cylinder and the deformed Virasoro algebra constructed earlier on an abstract mathematical background. As it was shown, the deformed Virasoro generators necessarily carry a second index (in addition to the usual one), whose meaning, however, remained unknown. The present field theoretical approach allows one to ascribe a clear meaning to this second index: its origin is related to the noncommutativity of the underlying space-time. The problems with the supersymmetric extension of the model on a noncommutative super-space are briefly discussed.
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Quantum Magnetic Collapse
We study the thermodynamics of degenerate electron and charged vector boson gases in very intense magnetic fields. In degenerate conditions of the electron gas, the pressure transverse to the magnetic field $B$ may vanish, leading to a transverse collapse. For W-bosons an instability arises because the magnetization diverges at the critical field B_c = M_W^2/e. If the magnetic field is self-consistently maintained, the maximum value it can take is of the order of $2B_c/3$, but in any case the system becomes unstable and collapses.
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