28 research outputs found
Vacuum Effects and Compressional Properties of Nuclear Matter in Cutoff Field Theory
Including the vacuum effects, the compressional properties of nuclear matter
are studied in the cutoff field theory. Under the Hartree approximation, the
low-energy effective Lagrangian is derived in the framework of the
renormalization group methods. The coefficients are determined in a way where
the physical results hardly depend on the value of the cutoff which is
conveniently introduced into the theory. It is shown that, to reproduce the
empirical data of the nucleus incompressibility, the compressibility of the
nuclear matter is favorable to be 250350MeV.Comment: PACS numbers, 21.65.+
Prompt High-Energy Emission from Proton-Dominated Gamma-Ray Bursts
The prompt emission of gamma-ray bursts (GRBs) is widely thought to be
radiation from accelerated electrons, but an appreciably larger amount of
energy could be carried by accelerated protons, particularly if GRBs are the
sources of ultra-high-energy cosmic rays (UHECRs). We model the expected photon
spectra for such "proton-dominated" GRBs in the internal shock scenario through
Monte Carlo simulations, accounting for various processes related to
high-energy electrons and protons. Besides proton and muon synchrotron
components, emission from photomeson-induced secondary pair cascades becomes
crucial, generally enhancing the GeV-TeV and/or eV-keV photons and offering a
signature of UHE protons. In some cases, it can overwhelm the primary electron
component and result in GRBs peaking in the 10 MeV - 1 GeV range, which may be
relevant to some bursts discussed in a recent re-analysis of EGRET TASC data.
The dependence of the spectra on key quantities such as the bulk Lorentz
factor, magnetic field and proton-to-electron ratio is nontrivial due to the
nonlinear nature of cascading and the interplay of electron- and proton-induced
components. Observations by {\it Fermi}, ground-based telescopes and other
facilities should test these expectations and provide critical constraints on
the proton acceleration efficiency.Comment: 16 pages, 6 figure
Near-Unity Singlet Fission on a Quantum Dot Initiated by Resonant Energy Transfer
The conversion of a high-energy photon into two excitons using singlet fission (SF) has stimulated a variety of studies in fields from fundamental physics to device applications. However, efficient SF has only been achieved in limited systems, such as solid crystals and covalent dimers. Here, we established a novel system by assembling 4-(6,13-bis(2-(triisopropylsilyl)ethynyl)pentacen-2-yl)benzoic acid (Pc) chromophores on nanosized CdTe quantum dots (QDs). A near-unity SF (198 ± 5.7%) initiated by interfacial resonant energy transfer from CdTe to surface Pc was obtained. The unique arrangement of Pc determined by the surface atomic configuration of QDs is the key factor realizing unity SF. The triplet-triplet annihilation was remarkably suppressed due to the rapid dissociation of triplet pairs, leading to long-lived free triplets. In addition, the low light-harvesting ability of Pc in the visible region was promoted by the efficient energy transfer (99 ± 5.8%) from the QDs to Pc. The synergistically enhanced light-harvesting ability, high triplet yield, and long-lived triplet lifetime of the SF system on nanointerfaces could pave the way for an unmatched advantage of SF.acceptedVersionPeer reviewe
Spectral Lag Relations in GRB Pulses Detected with HETE-2
Using a pulse-fit method, we investigate the spectral lags between the
traditional gamma-ray band (50-400 keV) and the X-ray band (6-25 keV) for 8
GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB
030528, GRB 040924, GRB 041006, GRB 050408) detected with the WXM and FREGATE
instruments aboard the HETE-2 satellite. We find several relations for the
individual GRB pulses between the spectral lag and other observables, such as
the luminosity, pulse duration, and peak energy (Epeak). The obtained results
are consistent with those for BATSE, indicating that the BATSE correlations are
still valid at lower energies (6-25 keV). Furthermore, we find that the photon
energy dependence for the spectral lags can reconcile the simple curvature
effect model. We discuss the implication of these results from various points
of view.Comment: 13 pages, 9 figures, accepted for the publication in PASJ (minor
corrections