The interference effects are studied and compared with for data sets from TEXONO, GEMMA, BOREXINO, LSND as well as CHARM II experiments. Our results provide more stringent bounds to some regions of parameter space.
Colladay and Kostelecký have proposed a framework for studying Lorentz and CPT violation in a natural extension of the standard model. Although numerous bounds exist on the Lorentz and CPT violating parameters in the gauge boson and fermion sectors, there are no published bounds on the parameters in the Higgs sector. We determine these bounds. The bounds on the CPT-even asymmetric coefficients arise from the one-loop contributions to the photon propagator, those from the CPT-even symmetric coefficients arise from the equivalent c coefficients in the fermion sector, and those from the CPT-odd coefficient arise from bounds on the vacuum expectation value of the Z boson.
We discuss and compare the effects of one extra dimension in the Randall Sundrum models on the evaluation of the Casimir force between two parallel plates. We impose the condition that the result reproduce the experimental measurements within the known uncertainties in the force and the plate separation, and get an upper bound kR 20 if the curvature parameter k of AdS 5 is equal to the Planck scale. Although the upper bound decreases as k decreases, kR ∼ 12, which is the required value for solving the hierarchy problem, is consistent with the Casimir force measurements.For the case where the 5 th dimension is infinite, the correction to the Casimir force is very small and negligible.
We analyse top quark flavor violating decays into a charm quark and a gluon, photon or Z boson in a supersymmetric model incorporating left-right symmetry. We include loop calculations involving contributions from scalar quarks, gluinos, charginos and neutralinos. We perform the calculations first assuming the minimal (flavor diagonal) scalar quark scenario, and then allowing for arbitrary mixing between the second and third generation of scalar quarks, in both the up and down sectors. In each case we present separately the contributions from gluino, chargino and neutralino loops and compare their respective strengths. In the flavor-diagonal case, the branching ratio cannot exceed 10 −5 (10 −6 ) for the gluon (photon/Z boson); while for the unconstrained (flavor non-diagonal) case the same branching ratios can reach almost 10 −4 for the gluon, 10 −6 for the photon and 10 −5 for the Z boson, all of which are slightly below the expected reach of LHC.
We systematically calculate various flavor-changing neutral-current top-quark processes induced by supersymmetry at the Large Hadron Collider, which include five decay modes and six production channels. To reveal the characteristics of these processes, we first compare the dependence of the rates for these channels on the relevant supersymmetric parameters, then we scan the whole parameter space to find their maximal rates, including all the direct and indirect current experimental constraints on the scharm-stop flavor mixings. We find that, under all these constraints, only a few channels, through cg → t at parton-level and t → ch, may be observable at the Large Hadron Collider.
We calculate the one-loop flavor changing neutral current top quark decay t → cgg in the Standard Model. We demonstrate that the rate for t → cgg exceeds the rate for a single gluon emission t → cg by about two orders of magnitude, while the rate for t → cqq, q = u is slightly smaller than for t → cg.
We study the effects of the minimal extension of the standard model including Lorentz violation on the Casimir force between two parallel conducting plates in vacuum. We provide explicit solutions for the electromagnetic field using scalar field analogy, for both the cases in which the Lorentz violating terms come from the CPT-even or CPT-odd terms. We also calculate the effects of the Lorentz violating terms for a fermion field between two parallel conducting plates and analyze the modifications of the Casimir force due to the modifications of the Dirac equation. In all cases under consideration, the standard formulas for the Casimir force are modified by either multiplicative or additive correction factors, the latter case exhibiting different dependence on the distance between the plates.The search for a theory beyond the minimal SU(3) C × SU(2) L × U(1) Y standard model (SM) is motivated by the fact that, although phenomenologically successful, the SM suffers from some theoretical inconsistencies, and from some long standing unresolved problems.More general scenarios exist, in which SM is viewed as a low-energy limit of more fundamental theory, which should be able to provide a quantum description of gravitation. An interesting alternative at the Planck scale is the possibility that the new physics scenario involves a violation of Lorentz symmetry. In particular, in the context of string theories, it has been shown that spontaneous breaking of Lorentz symmetry may occur with Lorentz-covariant dynamics [1]. In these theories, interactions are triggered by nonzero expectation values for Lorentz tensors, because spontaneous breaking of the higher-dimensional Lorentz invariance is expected in any realistic Lorentz-covariant fundamental theory involving more than four space-time dimensions. If the breaking extends into the four macroscopic spacetime dimensions, the Lorentz symmetry violation could appear at the level of the SM. Because the breaking is spontaneous, Lorentz symmetry remains a property of the underlying fundamental theory. Another important property of the spontaneous breaking is that the theory remains invariant under observer Lorentz transformations, i.e., under rotationsand boosts of an observer's inertial frame. In addition to that, conventional quantization, hermiticity, gauge invariance, power-counting renormalizability, and the expected microcausality and positivity of the energy are also maintained. Note also that there are other ways to break Lorentz symmetry. It can, for example, occur dynamically in quantum field theories [2], or via a CPT anomaly in compact spaces [3].Such a framework for examining the effects of spontaneous Lorentz breaking in the context of a low-energy effective theory, known as the Standard-Model Extension (SME), has been developed explicitly by Colladay and Kostelecký first without gravity [4] and later by Kostelecky with gravity [5]. Gravitationally coupled SME is described in non-Minkowski spacetimes and leads to spacetime-dependent coefficients; and recently, the ...
We evaluate the Casimir force between two parallel plates in Randall Sundrum (RS) scenarios extended by q compact dimensions. After giving exact expressions for one extra compact dimension (6D RS model), we generalize to an arbitrary number of compact dimensions. We present the complete calculation for both two brane scenario (RSI model) and one brane scenario (RSII model) using the method of summing over the modes. We investigate the effects of extra dimensions on the magnitude and sign of the force, and comment on limits for the size and number of the extra dimensions.
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