Supersymmetry, Naturalness, and Signatures at the LHC

Weak scale supersymmetry is often said to be fine-tuned, especially if the matter content is minimal. This is not true if there is a large A term for the top squarks. We present a systematic study on fine-tuning in minimal supersymmetric theories and identify low energy spectra that do not lead to severe fine-tuning. Characteristic features of these spectra are: a large A term for the top squarks, small top squark masses, moderately large tan\beta, and a small \mu parameter. There are classes of theories leading to these features, which are discussed. In one class, which allows a complete elimination of fine-tuning, the Higgsinos are the lightest among all the superpartners of the standard model particles, leading to three nearly degenerate neutralino/chargino states. This gives interesting signals at the LHC -- the dilepton invariant mass distribution has a very small endpoint and shows a particular shape determined by the Higgsino nature of the two lightest neutralinos. We demonstrate that these signals are indeed useful in realistic analyses by performing Monte Carlo simulations, including detector simulations and background estimations. We also present a method that allows the determination of all the relevant superparticle masses without using input from particular models, despite the limited kinematical information due to short cascades. This allows us to test various possible models, which is demonstrated in the case of a model with mixed moduli-anomaly mediation. We also give a simple derivation of special renormalization group properties associated with moduli mediated supersymmetry breaking, which are relevant in a model without fine-tuning.Comment: 56 pages, 24 figure

Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures

We investigated macroscopic quantum tunneling (MQT) of Bi$_2$Sr$_2$CaCu$_2$O$_y$ intrinsic Josephson junctions (IJJs) with two device structures. One is a nanometer-thick small mesa structure with only two or three IJJs and the other is a stack of a few hundreds of IJJs on a narrow bridge structure. Experimental results of switching current distribution for the first switching events from zero-voltage state showed a good agreement with the conventional theory for a single Josephson junction, indicating that a crossover temperature from thermal activation to MQT regime for the former device structure was as high as that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high-$T_c$ cuprates, independent of device structures. The switching current distribution for the second switching events from the first resistive state, which were carefully distinguished from the first switchings, was also compared between two device structures. In spite of the difference in the heat transfer environment, the second switching events for both devices were found to show a similar temperature-independent behavior up to a much higher temperature than the crossover temperature for the first switching. We argue that it cannot be explained in terms of the self-heating owing to dissipative currents after the first switching. As possible candidates, the MQT process for the second switching and the effective increase of electronic temperature due to quasiparticle injection are discussed.Comment: 10pages, 7figures, submitted to Phys. Rev.

Stability of Intercelular Exchange of Biochemical Substances Affected by Variability of Environmental Parameters

Communication between cells is realized by exchange of biochemical substances. Due to internal organization of living systems and variability of external parameters, the exchange is heavily influenced by perturbations of various parameters at almost all stages of the process. Since communication is one of essential processes for functioning of living systems it is of interest to investigate conditions for its stability. Using previously developed simplified model of bacterial communication in a form of coupled difference logistic equations we investigate stability of exchange of signaling molecules under variability of internal and external parameters.Comment: 11 pages, 3 figure

Geometrical parameter analysis of the high sensitivity fiber optic angular displacement sensor

In this work, we present an analysis of the influence of the geometrical parameters on the sensitivity and linear range of the fiber optic angular displacement sensor, through computational simulations and experiments. The geometrical parameters analyzed were the lens focal length, the gap between fibers, the fibers cladding radii, the emitting fiber critical angle (or, equivalently, the emitting fiber numerical aperture), and the standoff distance (distance between the lens and the reflective surface). Besides, we analyzed the sensor sensitivity regarding any spurious linear displacement. The simulation and experimental results showed that the parameters which play the most important roles are the emitting fiber core radius, the lens focal length, and the light coupling efficiency, while the remaining parameters have little influence on sensor characteristics. This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-53-36-8436. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Comment: 10 pages, 12 figure

Naturalized and simplified gauge mediation

Following recent developments in model building we construct a simple, natural and controllable model of gauge-mediated supersymmetry breaking.Comment: 8 pages, minor change

Geometry of One-Dimensional Wave Propagation

We investigate the geometrical features of one-dimensional wave propagation, whose dynamics is described by the (2+1)-dimensional Lorentz group. We find many interesting geometrical ingredients such as spinorlike behavior of wave amplitudes, gauge transformations, Bloch-type equations, and Lorentz-group Berry phases. We also propose an optical experiment to verify these effects.Comment: RevTeX, 16 pages, 6 postscript figure

Dynamic fluctuations in the superconductivity of NbN films from microwave conductivity measurements

We have measured the frequency and temperature dependences of complex ac conductivity, \sigma(\omega)=\sigma_1(\omega)-i\sigma_2(\omega), of NbN films in zero magnetic field between 0.1 to 10 GHz using a microwave broadband technique. In the vicinity of superconducting critical temperature, Tc, both \sigma_1(\omega) and \sigma_2(\omega) showed a rapid increase in the low frequency limit owing to the fluctuation effect of superconductivity. For the films thinner than 300 nm, frequency and temperature dependences of fluctuation conductivity, \sigma(\omega,T), were successfully scaled onto one scaling function, which was consistent with the Aslamazov and Larkin model for two dimensional (2D) cases. For thicker films, \sigma(\omega,T) data could not be scaled, but indicated that the dimensional crossover from three dimensions (3D) to 2D occurred as the temperature approached Tc from above. This provides a good reference of ac fluctuation conductivity for more exotic superconductors of current interest.Comment: 8 pages, 7 Figures, 1 Table, Accepted for publication in PR