68,001 research outputs found

    N-fold Parasupersymmetry

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    We find a new type of non-linear supersymmetries, called N-fold parasupersymmetry, which is a generalization of both N-fold supersymmetry and parasupersymmetry. We provide a general formulation of this new symmetry and then construct a second-order N-fold parasupersymmetric quantum system where all the components of N-fold parasupercharges are given by type A N-fold supercharges. We show that this system exactly reduces to the Rubakov-Spiridonov model when N=1 and admits a generalized type C 2N-fold superalgebra. We conjecture the existence of other `N-fold generalizations' such as N-fold fractional supersymmetry, N-fold orthosupersymmetry, and so on.Comment: 10 pages, no figures; Intro. expande

    Hands-on Physical Science Course at Radford University

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    Most students in our introductory physical science course are elementary education majors. We are faced with several obstacles in teaching basic science to these students. For example, they lack interest in science, logical thinking, and necessary data gathering and analysis skills, among others. Many of those obstacles could be traced back to the science courses they had taken in the past. Those courses put more emphasis on memorizing scientific facts than understanding natural phenomena or experiencing scientific methods. As a result, the students tend to have a negative attitude toward science in general. In order to reverse this attitude, We have been developing a hands-on, experience based physical science course. In each class students are asked to perform several experiments which require observation, data gathering, and analysis. The instructor provides necessary scientific background and explanation on the experiments as they go. One of the experiments the students enjoyed a lot is the measurement of average speeds of cars. They actually go out on the street and take data. Through this course students can experience how science works and learn that science could be more exciting than just memorizing

    DECIGO/BBO as a probe to constrain alternative theories of gravity

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    We calculate how strongly one can constrain the alternative theories of gravity with deci-Hz gravitational wave interferometers such as DECIGO and BBO. Here we discuss Brans-Dicke theory and massive graviton theories as typical examples. We consider the inspiral of compact binaries composed of a neutron star (NS) and an intermediate mass black hole (IMBH) for Brans-Dicke (BD) theory and those composed of a super massive black hole (SMBH) and a black hole (SMBH) for massive graviton theories. Using the restricted 2PN waveforms including spin effects and taking the spin precession into account, we perform the Monte Carlo simulations of 10410^4 binaries to estimate the determination accuracy of binary parameters including the Brans-Dicke parameter ωBD\omega_{\mathrm{BD}} and the graviton Compton length λg\lambda_g. Assuming a (1.4,10)M(1.4, 10)M_{\odot} NS/BH binary of SNR=200\sqrt{200}, the constraint on ωBD\omega_{\mathrm{BD}} is obtained as ωBD>2.32×106\omega_{\mathrm{BD}}>2.32\times 10^6, which is 300 times stronger than the estimated constraint from LISA observation. Furthermore, we find that, due to the expected large merger rate of NS/BH binaries of O(104)O(10^4) yr1^{-1}, a statistical analysis yields ωBD>3.77×108\omega_{\mathrm{BD}}>3.77\times10^8, which is 4 orders of magnitude stronger than the current strongest bound obtained from the solar system experiment. For massive graviton theories, assuming a (106,105)M(10^6, 10^5)M_{\odot} BH/BH binary at 3Gpc, one can put a constraint λg>3.35×1020\lambda_g>3.35\times10^{20}cm, on average. This is three orders of magnitude stronger than the one obtained from the solar system experiment. From these results, it is understood that DECIGO/BBO is a very powerful tool for constraining alternative theories of gravity, too.Comment: 4 pages, 3 figures; Accepted to Prog. Theor. Phys. Letters; Many interpretations and some references have been added; Some Coding errors being corrected and the final constraints came out stronge

    Particle production in models with helicity-0 graviton ghost in de Sitter spacetime

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    We revisit the problem of the helicity-0 ghost mode of massive graviton in the de Sitter background. In general, the presence of a ghost particle, which has negative energy, drives the vacuum to be unstable through pair production of ghost particles and ordinary particles. In the case that the vacuum state preserves the de Sitter invariance, the number density created by the pair production inevitably diverges due to unsuppressed ultra-violet(UV) contributions. In such cases one can immediately conclude that the model is not viable. However, in the massive gravity theory we cannot construct a vacuum state which respects the de Sitter invariance. Therefore the presence of a ghost does not immediately mean the breakdown of the model. Explicitly estimating the number density and the energy density of particles created by the pair production of two conformal scalar particles and one helicity-0 ghost graviton, we find that these densities both diverge. However, since models with helicity-0 ghost graviton have no de Sitter invariant vacuum state, it is rather natural to consider a UV cutoff scale in the three-dimensional momentum space. Then, even if we take the cutoff scale as large as the Planck scale, the created number density and energy density are well suppressed. In many models the cutoff scale is smaller than the Planck scale. In such models the created number density and the energy density are negligiblly small as long as only the physics below the cutoff scale is concerned.Comment: 7 pages, 1 figur

    Transport through a single Anderson impurity coupled to one normal and two superconducting leads

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    We study the interplay between the Kondo and Andreev-Josephson effects in a quantum dot coupled to one normal and two superconducting (SC) leads. In the large gap limit, the low-energy states of this system can be described exactly by a local Fermi liquid for the interacting Bogoliubov particles. The phase shift and the renormalized parameters for the Bogoliubov particles vary depending on the Josephson phase between the two SC leads. We explore the precise features of a crossover that occurs between the Kondo singlet and local Cooper-pairing states as the Josephson phase varies, using the numerical renormalization group approach.Comment: 4 pages, 4 figures, contribution to SCES 201
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