W-Y. Pauchy Hwang

Understanding the Core-Halo Relation of Quantum Wave Dark Matter from 3D Simulations

We examine the nonlinear structure of gravitationally collapsed objects that form in our simulations of wavelike cold dark matter, described by the Schrödinger-Poisson (SP) equation with a particle mass ∼10(-22)  eV. A distinct gravitationally self-bound solitonic core is found at the center of every halo, with a profile quite different from cores modeled in the warm or self-interacting dark matter scenarios. Furthermore, we show that each solitonic core is surrounded by an extended halo composed of large fluctuating dark matter granules which modulate the halo density on a scale comparable to the diameter of the solitonic core. The scaling symmetry of the SP equation and the uncertainty principle tightly relate the core mass to the halo specific energy, which, in the context of cosmological structure formation, leads to a simple scaling between core mass (Mc) and halo mass (Mh), Mc∝a(-1/2)Mh(1/3), where a is the cosmic scale factor. We verify this scaling relation by (i) examining the internal structure of a statistical sample of virialized halos that form in our 3D cosmological simulations and by (ii) merging multiple solitons to create individual virialized objects. Sufficient simulation resolution is achieved by adaptive mesh refinement and graphic processing units acceleration. From this scaling relation, present dwarf satellite galaxies are predicted to have kiloparsec-sized cores and a minimum mass of ∼10(8)M⊙, capable of solving the small-scale controversies in the cold dark matter model. Moreover, galaxies of 2×10(12)M⊙ at z=8 should have massive solitonic cores of ∼2×10(9)M⊙ within ∼60  pc. Such cores can provide a favorable local environment for funneling the gas that leads to the prompt formation of early stellar spheroids and quasars.

Inhomogeneity-induced cosmic acceleration in a dust universe

It is the common consensus that the expansion of a universe always slows down if the gravity provided by the energy sources therein is attractive and accordingly one needs to invoke dark energy as a source of anti-gravity for understanding the cosmic acceleration. To examine this point we find counterexamples for a spherically symmetric dust fluid described by the Lemaitre–Tolman–Bondi solution without singularity. Thus, the validity of this naive consensus is indeed doubtful and the effects of inhomogeneities should be restudied. These counter-intuitive examples open a new perspective on the understanding of the evolution of our universe.

Can the quintessence be a complex scalar field

Abstract In light of the recent observations of type Ia supernovae suggesting an accelerating expansion of the Universe, we wish in this Letter to point out the possibility of using a complex scalar field as the quintessence to account for the acceleration. In particular, we extend the idea of Huterer and Turner in deriving the reconstruction equations for the complex quintessence, showing the feasibility of making use of a complex scalar field (instead of a real scalar field) while maintaining the uniqueness feature of the reconstruction for two possible situations, respectively. We discuss very briefly how future observations may help to distinguish the different quintessence scenarios, including the scenario with a positive cosmological constant.

Measurement of Pressure Dependent Fluorescence Yield of Air: Calibration Factor for UHECR Detectors

In a test experiment at the Final Focus Test Beam of the Stanford Linear Accelerator Center, the fluorescence yield of 28.5 GeV electrons in air and nitrogen was measured. The measured photon yields between 300 and 400 nm at 1 atm and 29 deg C are Y(760 Torr, air) = 4.42 +/- 0.73 and Y(760 Torr, nitrogen) = 29.2 +/- 4.8 photons per electron per meter. Assuming that the fluorescence yield is proportional to the energy deposition of a charged particle traveling through air, good agreement with measurements at lower particle energies is observed.

The weak parity-violating pion-nucleon coupling

Abstract We use QCD sum rules to obtain the weak parity-violating pion-nucleon coupling constant f πNN . We find that f πNN ≈ 2 × 10 −8 , about an order of magnitude smaller than the “best estimates” based on quark models. This result follows from the cancellation between pertubative and nonperturbative QCD processes not found in quark models, but explicit in the QCD sum rule method. Our result is consistent with the experimental upper limit found from 18 F parity-violating measurements.

Hard form factors for meson-baryon strong couplings as derived from deep inelastic lepton scattering

As stimulated by earlier attempts for obtaining theπNN andπNδ form factors from the deep inelastic lepton scattering data, we extend the analysis by taking into account effects of additional mesons includingρ, Ω, σ,K, andK*, with the coupling constants fixed by the lowenergy nucleon-nucleon and hyperon-nucleon scattering data. Contrary to an earlier claim that theπ NN andπNδ form factor must be very soft (e.g., with the cutoff mass less than 500 MeV in the monopole form), we find, for example, that with all form factors parametrized in the dipole form, a universal cutoff mass of 1150 MeV in theδ/N sector and 1400 MeV in theλ/σ sector yields predictions in excellent agreement with recently published neutrino data on the momentum fractions carried by thes, Ū, and¯d quarks, as well as consistent with the sea-to-valence ratio extracted from the CDHS data and the Femilab E615 experiment. Similar results can also be obtained by using exponential cutoffs for all couplings, or by using monopole forms for some vertices while retaining dipole forms for the rest. The success of the mesonexchange picture in generating the strangeness content in a proton suggests an alternative understanding of the origin of sea quarks in the proton.

Parity violation in electron-deuteron scattering I. Methodology and elastic scattering

Abstract In this paper, we present methodology for investigating theoretically parity violation in both the elastic and break-up channels of electron-deuteron scattering, restricting ourselves to energies in which non-relativistic expansions are allowed for nucleons. The deficiency in the standard impulse approximation related to gauge invariance is remedied by relating it to the “elementary-particle” treatment. Results for parity violation in elastic electrondeuteron scattering are presented and discussed.

Signatures of noncommutative QED at photon colliders

In this paper we study non-commutative (NC) QED signatures at photon colliders through pair production of charged leptons(l + l ) and charged scalars(H + H ). The NC corrections for the fermion pair production can be easily obtained since NC QED with fermions has been extensively studied in the literature. NC QED with scalars is less studied. To obtain the cross section for H + H productions, we first investigate the structure of NC QED with scalars, and then study the corrections due to the NC geometry to the ordinary QED cross sections. Finally by folding in the photon spectra for a γγ collider with laser back-scattered photons from the e + e machine, we obtain 95% CL lower bound on the NC scale using the above two processes. We find that, with √ s = 0.5, 1.0, and 1.5 TeV and integrated luminosity L = 500(fb 1 ), the NC scale up to 0.7, 1.2, and 1.6 TeV can be probed, respectively, while, for monochromatic photon beams, these numbers become 1.1, 1.7, 2.6 TeV, respectively.

Accelerating universe as from the evolution of extra dimensions

In this paper we propose that the accelerating expansion of the present matter-dominated universe, as suggested by the recent distance measurements of type Ia supernovae, is generated along with the evolution of space in extra dimensions. The Einstein equations are first analyzed qualitatively and then solved numerically, so as to exhibit explicitly these patterns of the accelerating expansion in this scenario. A fine-tuning problem associated with such a scenario is also described and discussed.

QCD sum rules: Delta - N and Sigma0 - Lambda mass splittings

We use the method of QCD sum rules to investigate both the [Delta]-[ital N] and [Sigma][sup 0-][Lambda] mass splittings. In the case of the [Delta]-[ital N] mass splitting, our numerical results indicate that the mass splitting is dominated primarily by the quark-gluon condensate [l angle]0[vert bar][ital g][sub [ital c][bar q]][sigma][sub [mu][nu]]([lambda][sup [ital a]]/2)[ital G][sub [ital a]][sup [mu][nu]][ital q][vert bar]0[r angle] and the observed mass splitting may be understood. In the case of [Sigma][sup 0-][Lambda] mass splitting, we obtain a value of about 66 MeV, which is slightly smaller than the observed value of 77 MeV.