Generalized Cahn effect and parton 3D motion in a covariant approach

The Cahn effect and the unintegrated unpolarized parton distribution function $f_{1}^{q}(x,\mathbf{p}_{T})$ are studied in a covariant approach. The Cahn effect is compared with some other effects due to the parton intrinsic motion. The comparison suggests that the present understanding of parton transverse momenta and intrinsic motion in general is still rather incomplete. The new relation for $f_{1}^{q}(x,\mathbf{p}_{T})$ is obtained in the framework of the covariant parton model from which a prediction for this distribution function follows.Comment: 8 pages, 2 figures. Updated version is accepted for publication in Phys.Rev.

Singularity avoidance by collapsing shells in quantum gravity

We discuss a model describing exactly a thin spherically symmetric shell of matter with zero rest mass. We derive the reduced formulation of this system in which the variables are embeddings, their conjugate momenta, and Dirac observables. A non-perturbative quantum theory of this model is then constructed, leading to a unitary dynamics. As a consequence of unitarity, the classical singularity is fully avoided in the quantum theory.Comment: 5 pages, 1 figure, received honorable mention in the 2001 essay competititon, to appear in Int. J. Mod. Phys.

M-Theory Through the Looking Glass: Tachyon Condensation in the E_8 Heterotic String

We study the spacetime decay to nothing in string theory and M-theory. First we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles of nothing -- connecting the two E_8 boundaries by a throat -- are expected to be nucleated. We argue that the fate of this system should be addressed at weak string coupling, where the nonperturbative instanton instability is expected to turn into a perturbative tachyonic one. We identify the unique string theory that could describe this process: The heterotic model with one E_8 gauge group and a singlet tachyon. We then use worldsheet methods to study the tachyon condensation in the NSR formulation of this model, and show that it induces a worldsheet super-Higgs effect. The main theme of our analysis is the possibility of making meaningful alternative gauge choices for worldsheet supersymmetry, in place of the conventional superconformal gauge. We show in a version of unitary gauge how the worldsheet gravitino assimilates the goldstino and becomes dynamical. This picture clarifies recent results of Hellerman and Swanson. We also present analogs of R_\xi gauges, and note the importance of logarithmic CFT in the context of tachyon condensation.Comment: 36 pages, 1 figur

Economic optimization of component sizing for residential battery storage systems

Battery energy storage systems (BESS) coupled with rooftop-mounted residential photovoltaic (PV) generation, designated as PV-BESS, draw increasing attention and market penetration as more and more such systems become available. The manifold BESS deployed to date rely on a variety of different battery technologies, show a great variation of battery size, and power electronics dimensioning. However, given today's high investment costs of BESS, a well-matched design and adequate sizing of the storage systems are prerequisites to allow profitability for the end-user. The economic viability of a PV-BESS depends also on the battery operation, storage technology, and aging of the system. In this paper, a general method for comprehensive PV-BESS techno-economic analysis and optimization is presented and applied to the state-of-art PV-BESS to determine its optimal parameters. Using a linear optimization method, a cost-optimal sizing of the battery and power electronics is derived based on solar energy availability and local demand. At the same time, the power flow optimization reveals the best storage operation patterns considering a trade-off between energy purchase, feed-in remuneration, and battery aging. Using up to date technology-specific aging information and the investment cost of battery and inverter systems, three mature battery chemistries are compared; a lead-acid (PbA) system and two lithium-ion systems, one with lithium-iron-phosphate (LFP) and another with lithium-nickel-manganese-cobalt (NMC) cathode. The results show that different storage technology and component sizing provide the best economic performances, depending on the scenario of load demand and PV generation.Web of Science107art. no. 83

Coherent and Squeezed Vacuum Light Interferometry: Parity detection hits the Heisenberg limit

The interference between coherent and squeezed vacuum light can produce path entangled states with very high fidelities. We show that the phase sensitivity of the above interferometric scheme with parity detection saturates the quantum Cramer-Rao bound, which reaches the Heisenberg-limit when the coherent and squeezed vacuum light are mixed in roughly equal proportions. For the same interferometric scheme, we draw a detailed comparison between parity detection and a symmetric-logarithmic-derivative-based detection scheme suggested by Ono and Hofmann.Comment: Change in the format from aps to iop since we decided to submit it to NJP; Minor changes in tex

General Covariance in Quantum Gravity at a Lifshitz Point

In the minimal formulation of gravity with Lifshitz-type anisotropic scaling, the gauge symmetries of the system are foliation-preserving diffeomorphisms of spacetime. Consequently, compared to general relativity, the spectrum contains an extra scalar graviton polarization. Here we investigate the possibility of extending the gauge group by a local U(1) symmetry to "nonrelativistic general covariance." This extended gauge symmetry eliminates the scalar graviton, and forces the coupling constant $\lambda$ in the kinetic term of the minimal formulation to take its relativistic value, $\lambda=1$. The resulting theory exhibits anisotropic scaling at short distances, and reproduces many features of general relativity at long distances.Comment: 41 pages; v2: small clarifications, references adde

Resonant Activation Phenomenon for Non-Markovian Potential-Fluctuation Processes

We consider a generalization of the model by Doering and Gadoua to non-Markovian potential-switching generated by arbitrary renewal processes. For the Markovian switching process, we extend the original results by Doering and Gadoua by giving a complete description of the absorption process. For all non-Markovian processes having the first moment of the waiting time distributions, we get qualitatively the same results as in the Markovian case. However, for distributions without the first moment, the mean first passage time curves do not exhibit the resonant activation minimum. We thus come to the conjecture that the generic mechanism of the resonant activation fails for fluctuating processes widely deviating from Markovian.Comment: RevTeX 4, 5 pages, 4 figures; considerably shortened version accepted as a brief report to Phys. Rev.

Ab initio many-body calculations of nucleon scattering on 4He, 7Li, 7Be, 12C and 16O

We combine a recently developed ab initio many-body approach capable of describing simultaneously both bound and scattering states, the ab initio NCSM/RGM, with an importance truncation scheme for the cluster eigenstate basis and demostrate its applicability to nuclei with mass numbers as high as 17. Using soft similarity renormalization group evolved chiral nucleon-nucleon interactions, we first calculate nucleon-4He phase shifts, cross sections and analyzing power. Next, we investigate nucleon scattering on 7Li, 7Be, 12C and 16O in coupled-channel NCSM/RGM calculations that include low-lying excited states of these nuclei. We check the convergence of phase shifts with the basis size and study A=8, 13, and 17 bound and unbound states. Our calculations predict low-lying resonances in 8Li and 8B that have not been experimentally clearly identified yet. We are able to reproduce reasonably well the structure of the A=13 low lying states. However, we find that A=17 states cannot be described without an improved treatment of 16O one-particle-one-hole excitations and alpha clustering.Comment: 18 pages, 20 figure