649 research outputs found
Observing dynamical supersymmetry breaking with euclidean lattice simulations
A strict positivity of the ground-state energy is a necessary and sufficient
condition for spontaneous supersymmetry breaking. This ground-state energy may
be directly determined from the expectation value of the Hamiltonian in the
functional integral, defined with an \emph{antiperiodic} temporal boundary
condition for all fermionic variables. We propose to use this fact to observe
the dynamical spontaneous supersymmetry breaking in Euclidean lattice
simulations. If a lattice formulation possesses a manifestly preserved
fermionic symmetry, there exists a natural choice of a Hamiltonian operator
that is consistent with a topological nature of the Witten index. We
numerically confirm the validity of our idea in models of supersymmetric
quantum mechanics. We further examine the possibility of dynamical
supersymmetry breaking in the two-dimensional super
Yang-Mills theory with the gauge group SU(2), for which the Witten index is
unknown. Although statistical errors are still large, we do not observe
positive ground-state energy, at least within one standard deviation. This
prompts us to draw a different conclusion from a recent conjectural claim that
supersymmetry is dynamically broken in this system.Comment: 35 pages, 9 figures, the final version to appear in Prog. Theor. Phy
Sequentially Timed All-Optical Mapping Photography for Real- Time Monitoring of Laser Ablation: Breakdown and Filamentation in Picosecond and Femtosecond Regimes
To investigate ultrafast phenomena, a novel, ultrafast imaging technique was developed. Sequentially timed all-optical mapping photography (STAMP) performs single-shot image acquisition without the need for repetitive measurements and without sacrificing high-temporal resolution and image quality. The principle of this imaging method is based on the all-optical approach, and therefore it overcomes the temporal resolution in conventional high-speed cameras. Also, STAMP’s single-shot movie-shooting capability allows us to obtain sequential images of non-repetitive ultrafast dynamic phenomena. Here, we present the motion pictures of early stage dynamics during femtosecond laser ablation captured by two types of STAMP setup. Breakdown was induced by intense femtosecond laser pulse and monitored with a frame interval of 15.3 ps and a total of six frames. The movie clearly shows the plasma generation and expansion on glass surface. Also, filamentation was generated inside a glass and observed with a frame interval of 230 fs and total of 25 frames. These phenomena have previously only been observed by pump-probe imaging. STAMP is a powerful tool to understand precise processes of complex dynamics in ultrashort laser ablation
Practical purification scheme for decohered coherent-state superpositions via partial homodyne detection
We present a simple protocol to purify a coherent-state superposition that
has undergone a linear lossy channel. The scheme constitutes only a single beam
splitter and a homodyne detector, and thus is experimentally feasible. In
practice, a superposition of coherent states is transformed into a classical
mixture of coherent states by linear loss, which is usually the dominant
decoherence mechanism in optical systems. We also address the possibility of
producing a larger amplitude superposition state from decohered states, and
show that in most cases the decoherence of the states are amplified along with
the amplitude.Comment: 8 pages, 10 figure
Mechanistic species distribution modeling reveals a niche shift during invasion
Niche shifts of nonnative plants can occur when they colonize novel climatic conditions. However, the mechanistic basis for niche shifts during invasion is poorly understood and has rarely been captured within species distribution models. We quantified the consequence of between-population variation in phenology for invasion of common ragweed (Ambrosia artemisiifolia L.) across Europe. Ragweed is of serious concern because of its harmful effects as a crop weed and because of its impact on public health as a major aeroallergen. We developed a forward mechanistic species distribution model based on responses of ragweed development rates to temperature and photoperiod. The model was parameterized and validated from the literature and by reanalyzing data from a reciprocal common garden experiment in which native and invasive populations were grown within and beyond the current invaded range. It could therefore accommodate between-population variation in the physiological requirements for flowering, and predict the potentially invaded ranges of individual populations. Northern-origin populations that were established outside the generally accepted climate envelope of the species had lower thermal requirements for bud development, suggesting local adaptation of phenology had occurred during the invasion. The model predicts that this will extend the potentially invaded range northward and increase the average suitability across Europe by 90% in the current climate and 20% in the future climate. Therefore, trait variation observed at the population scale can trigger a climatic niche shift at the biogeographic scale. For ragweed, earlier flowering phenology in established northern populations could allow the species to spread beyond its current invasive range, substantially increasing its risk to agriculture and public health. Mechanistic species distribution models offer the possibility to represent niche shifts by varying the traits and niche responses of individual populations. Ignoring such effects could substantially underestimate the extent and impact of invasions
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