arXiv subjects

C. -P. Liu

Publications and source records attributed to C. -P. Liu.

At least 37 records · Page 2Linked to original sources

arXiv2012

Near Threshold Proton-Proton Fusion in Effective Field Theory

The astrophysical S-factor for proton-proton fusion, S_11(E), is obtained with the nuclear matrix element analytically calculated in pionless effective field theory. To the third order, the zero-energy result S_11(0) and the first energy derivative S'_11(0) are found to be (3.99 \pm 0.14)* 10^-25 MeV b and S_11(0)*(11.3 \pm 0.1) MeV^-1, respectively; both consistent with the current adopted values. The second energy derivative is also calculated for the first time, and the result S"_11(0) = S_11(0)*(170 \pm 2) MeV^-2 contributes at the level of 0.5% to the fusion rate at the solar center, which is smaller than 1% as previously estimated.

nucl-th↗

arXiv2012

Deuteron Magnetic Quadrupole Moment From Chiral Effective Field Theory

We calculate the magnetic quadrupole moment (MQM) of the deuteron at leading order in the systematic expansion provided by chiral effective field theory. We take into account parity and time-reversal violation which, at the quark-gluon level, results from the QCD vacuum angle and dimension-six operators that originate from physics beyond the Standard Model. We show that the deuteron MQM can be expressed in terms of five low-energy constants that appear in the parity- and time-reversal-violating nuclear potential and electromagnetic current, four of which also contribute to the electric dipole moments of light nuclei. We conclude that the deuteron MQM has an enhanced sensitivity to the QCD vacuum angle and that its measurement would be complementary to the proposed measurements of light-nuclear EDMs.

hep-ph↗

arXiv2011

Electric Dipole Moments of Light Nuclei From Chiral Effective Field Theory

We set up the framework for the calculation of electric dipole moments (EDMs) of light nuclei using the systematic expansion provided by chiral effective field theory (EFT). We take into account parity (P) and time-reversal (T) violation which, at the quark-gluon level, originates from the QCD vacuum angle and dimension-six operators capturing physics beyond the Standard Model. We argue that EDMs of light nuclei can be expressed in terms of six low-energy constants that appear in the P- and T-violating nuclear potential and electric current. As examples, we calculate the EDMs of the deuteron, the triton, and 3He in leading order in the EFT expansion.

hep-ph↗

arXiv2010

On the Quark Mass Dependence of Two Nucleon Observables

We study the implications of lattice QCD determinations of the S-wave nucleon-nucleon scattering lengths at unphysical light quark masses. It is found that with the help of nuclear effective field theory (NEFT), not only the quark mass dependence of the effective range parameters, but also the leading quark mass dependence of all the low energy deuteron matrix elements can be obtained. The quark mass dependence of deuteron charge radius, magnetic moment, polarizability and the deuteron photodisintegration cross section are shown based on the NPLQCD lattice calculation of the scattering lengths at 354 MeV pion mass and the NEFT power counting scheme of Beane, Kaplan and Vuorinen. Further improvement can be obtained by performing the lattice calculation at smaller quark masses. Our result can be used to constrain the time variation of isoscalar combination of u and d quark mass m_q, to help the anthropic principle study to find the m_q range which allows the existence of life, and to provide a weak test of the multiverse conjecture.

nucl-th↗

arXiv2009

Surface optical phonon modes in ternary aligned crystalline InGaN-GaN multi-quantum well nanopillar arrays

The optical properties of focused ion beam-engraved perfectly aligned and spatially controlled multi-quantum-well InGaN-GaN nanopillars were investigated. Crystalline MQW nanopillars with a diameter of 30 to 95 nm and high aspect ratios showed a maximum of three-fold enhancement in emission intensity per unit active area. A light emitting contour map of Taiwan is drawn with a nanopillar structure to demonstrate the site control of the technique adopted in the present study. Raman scattering studies were used to characterize the newly created surfaces. Unknown peaks in GaN and InGaN nanostructures are identified for surface optical (SO) phonon modes with proper assignments of wave vectors using multiple excitations, and the SO mode for the ternary phase is reported for the first time.

cond-mat.mtrl-sci↗

arXiv2008

Nuclear Electric Dipole Moment of 3He

A permanent electric dipole moment (EDM) of a physical system requires time-reversal (T) and parity (P) violation. Experimental programs are currently pushing the limits on EDMs in atoms, nuclei, and the neutron to regimes of fundamental theoretical interest. Here we calculate the magnitude of the PT-violating EDM of 3He and the expected sensitivity of such a measurement to the underlying PT-violating interactions. Assuming that the coupling constants are of comparable magnitude for pi-, rho-, and omega-exchanges, we find that the pion-exchange contribution dominates. Our results suggest that a measurement of the 3He EDM is complementary to the planned neutron and deuteron experiments, and could provide a powerful constraint for the theoretical models of the pion-nucleon PT-violating interaction.

nucl-th↗

arXiv2008

Parity-violating nucleon-nucleon interaction from different approaches

Two-pion exchange parity-violating nucleon-nucleon interactions from recent effective field theories and earlier fully covariant approaches are investigated. The potentials are compared with the idea to obtain better insight on the role of low-energy constants appearing in the effective field theory approach and the convergence of this one in terms of a perturbative series. The results are illustrated by considering the longitudinal asymmetry of polarized protons scattering off protons, $\vec{p}+p -> p+p$, and the asymmetry of the photon emission in radiative capture of polarized neutrons by protons, $\vec{n}+p -> d+γ$.

nucl-th↗

arXiv2008

The old and the new of parity-violating two-pion-exchange $NN$ potential

We consider the parity-violating two-pion-exchange potential obtained from the covariant formalism in the past and the state-of-the-art effective field theory approach. We discuss the behavior of the potential in coordinate space and its application to the parity-violating asymmetry in $\vec{n} p \to d γ$ at threshold.

nucl-th↗

arXiv2007

Schiff Screening of Relativistic Nucleon Electric-Dipole Moments by Electrons

We show, at leading-order in the multipole expansion of the electron-nucleus interaction, that nucleon electric-dipole moments are completely shielded by electrons so that they contribute nothing to atomic electric-dipole moments, even when relativity in the nucleus is taken into account. It is well known that relativistic electron motion, by contrast, leads to dipole moments that are not screened; we discuss the reasons for the difference.

nucl-th↗

arXiv2007

Atomic Electric Dipole Moments: The Schiff Theorem and Its Corrections

Searches for the permanent electric dipole moments (EDMs) of diamagnetic atoms provide powerful probes of CP-violating hadronic and semileptonic interactions. The theoretical interpretation of such experiments, however, requires careful implementation of a well-known theorem by Schiff that implies a vanishing net EDM for an atom built entirely from point-like, nonrelativistic constituents that interact only electrostatically. Any experimental observation of a nonzero atomic EDM would result from corrections to the point-like, nonrelativistic, electrostatic assumption. We reformulate Schiff's theorem at the operator level and delineate the electronic and nuclear operators whose atomic matrix elements generate corrections to "Schiff screening". We obtain a form for the operator responsible for the leading correction associated with finite nuclear size -- the so-called "Schiff moment" operator -- and observe that it differs from the corresponding operator used in previous Schiff moment computations. We show that the more general Schiff moment operator reduces to the previously employed operator only under certain approximations that are not generally justified. We also identify other corrections to Schiff screening that may not be included properly in previous theoretical treatments. We discuss practical considerations for obtaining a complete computation of corrections to Schiff screening in atomic EDM calculations.

nucl-th↗

arXiv2007

Strangeness-Conserving Hadronic Parity Violation at Low Energies

The parity-violating nucleon-nucleon interaction is the key to understanding the strangeness-conserving hadronic weak interaction at low energies. In this brief talk, I review the past accomplishments in and current status of this subject, and outline a new joint effort between experiment and theory that tries to address the potential problems in the past by focusing on parity violation in few-nucleon systems and using the language of effective field theory.

nucl-th↗

arXiv2006

Parity-Violating Observables of Two-Nucleon Systems in Effective Field Theory

A newly-proposed parity-violating nucleon-nucleon interaction based on effective field theory is studied in this work. It is found that at low energy, i.e., E_lab less than 90 MeV for 1S0-3P0 transitions and E_lab less than 40 MeV for 3S1-1P1 and 3S1-3P1 transitions, the parity-violating observables can be completely specified by a minimal set of six parameters. It contains five low-energy constants, which are equivalent to the Danilov parameters, and an additional parameter that characterizes the long-range one-pion exchange and is proportional to the parity-violating pion-nucleon coupling constant. Selected observables in two-nucleons systems are analyzed in this framework with their dependence on these parameters being expressed in a nearly model-independent way.

nucl-th↗

arXiv2006

Time-Reversal Violation in Threshold $\vec{n}$ $\vec{p}$ Scattering

We investigate parity and time-reversal violation in neutron-proton scattering in the optical regime. We calculate the neutron spin rotation and analyzing power in scattering on polarized protons. This allows us to quantify the sensitivity that such experiments should aim for in order to be competitive to present-day measurements of the neutron electric dipole moment in constraining the $P$- and $T$-odd two-nucleon interaction. While state-of-the-art techniques fall short by some three orders of magnitude for the neutron-proton case, specific neutron-nucleus experiments look promising, provided certain experimental and theoretical challenges are met.

nucl-th↗

arXiv2006

Schiff Theorem and the Electric Dipole Moments of Hydrogen-Like Atoms

The Schiff theorem is revisited in this work and the residual $P$- and $T$-odd electron--nucleus interaction, after the shielding takes effect, is completely specified. An application is made to the electric dipole moments of hydrogen-like atoms, whose qualitative features and systematics have important implication for realistic paramagnetic atoms.

nucl-th↗

arXiv2005

Parity Nonconservation in Elastic $\vec{p} p$ Scattering

By looking at the parity-nonconserving (PNC) asymmetries at different energies in $\vec{p} p$ scattering, it is in principle possible to determine the PNC $ρNN$ and $ωNN$ couplings of a single-meson-exchange model of the PNC $NN$ force. The analysis of the experimental data at 13.6, 45 and 221 MeV simultaneously has been performed by Carlson \textit{et al.}, who concluded to an agreement with the original DDH estimates for the PNC meson-nucleon couplings. In this work, it is shown first that the comparison with updated hadronic predictions of these couplings rather suggests the existence of some discrepancy for the PNC $ωNN$ coupling. The effect of variations on the strong coupling constants and introduction of cutoffs in the one-boson-exchange weak potential is then investigated. As expected, it turns out that the resulting asymmetry is quite sensitive to these parameters regardless of the energy. However the above discrepancy persists. The dependence of this conclusion on various ingredients entering an improved description of the PNC $NN$ force is also examined. These include the two-pion resonance nature of the rho meson and some momentum dependence of the isoscalar PNC $ρNN$ vertex. It is found that none of these corrections is able to remove or even alleviate the above discrepancy. Their impacts on the theoretical determination of the vector meson-nucleon couplings, the description of the PNC force in terms of single-meson exchanges, or the interpretation of measurements, are finally examined.

nucl-th↗

arXiv2005

Parity violation in $pp$ scattering and vector-meson weak-coupling constants

We calculate the parity-nonconserving longitudinal asymmetry in the elastic $\vec{p} p$ scattering at the energies where experimental data are available. In addition to the standard one-meson exchange weak potential, the variation of the strong-coupling constants and the non-standard effects such as form factors and $2 π$-exchange description of the $ρ$-exchange potential are taken into account. With the extra effects, we investigate the compatibility of the experimental data and the presently-known range of the vector-meson weak-coupling constants.

nucl-th↗

arXiv2004

$P$- and $T$-odd two-nucleon interaction and the deuteron electric dipole moment

The nuclear physics relevant to the electric dipole moment (EDM) of the deuteron is addressed. The general operator structure of the $P$- and $T$-odd nucleon-nucleon interaction is discussed and applied to the two-body contributions of the deuteron EDM, which can be calculated in terms of $P$- and $T$-odd meson-nucleon coupling constants with only small model dependence. The one-body contributions, the EDMs of the proton and the neutron, are evaluated within the same framework. Although the total theoretical uncertainties are sizable, we conclude that, compared to the neutron, the deuteron EDM is competitive in terms of sensitivity to $C P$ violation, and complementary with respect to the microscopic sources of $C P$ violation that can be probed.

nucl-th↗

arXiv2004

Parity Nonconservation in the Photodisintegration of the Deuteron at Low Energy

The parity-nonconserving asymmetry in the deuteron photodisintegration, $\vecγ+d\to n+p$, is considered with the photon energy ranged up to 10 MeV above the threshold. The aim is to improve upon a schematic estimate assuming the absence of tensor as well as spin-orbit forces in the nucleon-nucleon interaction. The major contributions are due to the vector-meson exchanges, and the strong suppression of the pion-exchange contribution is confirmed. A simple argument, going beyond the observation of an algebraic cancellation, is presented. Contributions of meson-exchange currents are also considered, but found to be less significant.

nucl-th↗