Neutrino-nucleus elastic scattering provides a unique laboratory to study the quantum mechanical ... more Neutrino-nucleus elastic scattering provides a unique laboratory to study the quantum mechanical coherency effects in electroweak interactions, towards which several experimental programs are being actively pursued. We report results of our quantitative studies on the transitions towards decoherency. A parameter (α) is identified to describe the degree of coherency, and its variations with incoming neutrino energy, detector threshold and target nucleus are studied. The ranges of α which can be probed with realistic neutrino experiments are derived, indicating complementarity between projects with different sources and targets. Uncertainties in nuclear physics and in α would constrain sensitivities in probing physics beyond the standard model. The maximum neutrino energies corresponding to α>0.95 are derived.
We calculate isospin 2 pion-pion scattering in chiral perturbation theory for a partially quenche... more We calculate isospin 2 pion-pion scattering in chiral perturbation theory for a partially quenched, mixed action theory with Ginsparg-Wilson valence quarks and staggered sea quarks. We point out that for some scattering channels, the power-law volume dependence of two-pion states in nonunitary theories such as partially quenched or mixed action QCD is identical to that of QCD. Thus one can extract infinite-volume scattering parameters from mixed action simulations. We then determine the scattering length for both 2 and 2 1 sea quarks in the isospin limit. The scattering length, when expressed in terms of the pion mass and the decay constant measured on the lattice, has no contributions from mixed valence-sea mesons, thus it does not depend upon the parameter, C Mix , that appears in the chiral Lagrangian of the mixed theory. In addition, the contributions which nominally arise from operators appearing in the mixed action Oa 2 m q Lagrangian exactly cancel when the scattering length is written in this form. This is in contrast to the scattering length expressed in terms of the bare parameters of the chiral Lagrangian, which explicitly exhibits all the sicknesses and lattice spacing dependence allowed by a partially quenched mixed action theory. These results hold for both 2 and 2 1 flavors of sea quarks.
The ratio η/s, shear viscosity (η) to entropy density (s), reaches its local minimum at the (seco... more The ratio η/s, shear viscosity (η) to entropy density (s), reaches its local minimum at the (second order) phase transition temperature in a wide class of systems. It was suspected that this behavior might be universal. However, a counterexample is found in a system of two weakly self-interacting real scalar fields with one of them condensing at low temperatures while the other remains in the symmetric phase. There is no interaction between the two fields. The resulting η/s is monotonically decreasing in temperature despite the phase transition.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2013
From ultracold atoms to quantum chromodynamics, reliable ab initio studies of strongly interactin... more From ultracold atoms to quantum chromodynamics, reliable ab initio studies of strongly interacting fermions require numerical methods, typically in some form of quantum Monte Carlo. Unfortunately, (non-)relativistic systems at finite density (spin polarization) generally have a sign problem, such that those ab initio calculations are impractical. It is well known, however, that in the relativistic case imaginary chemical potentials solve this problem, assuming the data can be analytically continued to the real axis. Is this feasible for non-relativistic systems? Are the interesting features of the phase diagram accessible in this manner? Introducing complex chemical potentials, for real total particle number and imaginary polarization, the sign problem is avoided in the non-relativistic case. To give a first answer to the above questions, we perform a mean-field study of the finite-temperature phase diagram of spin-1/2 fermions with imaginary polarization.
The scalar and tensor polarizabilities of the deuteron are calculated using the recently develope... more The scalar and tensor polarizabilities of the deuteron are calculated using the recently developed effective field theory that describes nucleon-nucleon interactions. Leading and next-to-leading order contributions in the perturbative expansion predict a scalar electric polarizability of α E0 = 0.595 fm 3. The tensor electric polarizability receives contributions starting at next-toleading order from the exchange of a single potential pion and is found to be α E2 = −0.062 fm 3. We compute the leading contributions to the scalar and tensor magnetic polarizabilities, finding β M 0 = 0.067 fm 3 and β M 2 = 0.195 fm 3 .
The cross section for np → dγ is calculated at energies relevant to bigbang nucleosynthesis using... more The cross section for np → dγ is calculated at energies relevant to bigbang nucleosynthesis using the recently developed effective field theory that describes the two-nucleon sector. The E1 amplitude is computed up to N 3 LO and depends only upon nucleon-nucleon phase shift data. In contrast, the M1 contribution is computed up to NLO, and the four-nucleon-one-magneticphoton counterterm that enters is determined by the cross section for cold neutron capture. The uncertainty in the calculation for nucleon energies up to E ∼ 1 MeV is estimated to be < ∼ 4%.
Deuteron Compton scattering is calculated to O(Q 2) in pionless effective field theory using a di... more Deuteron Compton scattering is calculated to O(Q 2) in pionless effective field theory using a dibaryon approach. The vector amplitude, which was not included in the previous pionless calculations, contributes to the cross section at O(Q 2) and influences significantly the extracted values of nucleon electric polarizability at incident photon energy 49 MeV. We recommend future high precision deuteron compton scattering experiments being performed at 25-35 MeV photon energy where the nucleon polarizability effects are appreciable and the pionless effective field theory is most reliable. For example, a measurement at 30 MeV with a 3% error will constrain the isoscalar nucleon electric polarizability α 0 with a ∼ 30% error.
Parton convolution models have been used extensively in describing the sea quarks in the nucleon ... more Parton convolution models have been used extensively in describing the sea quarks in the nucleon and explaining quark distributions in nuclei (the EMC effect). From effective field theory point of view, we construct the parton convolution formalism which has been the underlying conception of all convolution models. We explain the significance of scheme and scale dependence of the auxiliary quantities such as the pion distributions in a nucleon. As an application, we calculate the complete leading nonanalytic chiral contribution to the isovector component of the nucleon sea.
Using chiral perturbation theory we investigate the QCD shear viscosity (η) to entropy density (s... more Using chiral perturbation theory we investigate the QCD shear viscosity (η) to entropy density (s) ratio below the deconfinement temperature (∼ 170 MeV) with zero baryon number density. It is found that η/s of QCD is monotonically decreasing in temperature (T) and reaches 0.6 with estimated ∼ 50% uncertainty at T = 120 MeV. A naive extrapolation of the leading order result shows that η/s reaches the 1/4π minimum bound proposed by Kovtun, Son, and Starinets using string theory methods at T ∼ 200 MeV. This suggests a phase transition or cross over might occur at T 200 MeV in order for the bound to remain valid. Also, it is natural for η/s to stay close to the minimum bound around the phase transition temperature as was recently found in heavy ion collisions.
I summarize the motivation for the effective field theory approach to nuclear physics, and some o... more I summarize the motivation for the effective field theory approach to nuclear physics, and some of its recent accomplishments.
The UV-Cutoff Effects on the Chiral Critical Surface in Hot and Dense QCD
Nucleation and Atmospheric Aerosols, 2011
ABSTRACT The search of the QCD critical point is one of the interesting issues both in theoretica... more ABSTRACT The search of the QCD critical point is one of the interesting issues both in theoretical and experimental particle physics. In this article, we use the Nambu Jona-Lasinio model to study the UV-cutoff effects on the critical surface which may play a crucial role to the possible existence/non-existence of the critical point. Then we compare the indications between the results obtained through our effective approach and the lattice QCD simulations.
We study the Bell inequality in a holographic model of the casually disconnected Einstein-Podolsk... more We study the Bell inequality in a holographic model of the casually disconnected Einstein-Podolsky-Rosen (EPR) pair. The Clauser-Horne-Shimony-Holt(CHSH) form of Bell inequality is constructed using holographic Schwinger-Keldysh (SK) correlators. We show that the manifestation of quantum correlation in Bell inequality can be holographically reproduced from the classical fluctuations of dual accelerating string in the bulk gravity. The violation of this holographic Bell inequality supports the essential quantum property of this holographic model of an EPR pair.
We investigate the renormalon ambiguity from bubble-chain diagrams in the isovector unpolarized q... more We investigate the renormalon ambiguity from bubble-chain diagrams in the isovector unpolarized quasi-parton distribution function (PDF) of a hadron. We confirm the assertion by Braun, Vladimirov and Zhang [1] that the leading IR renormalon ambiguity is an O(Λ 2 QCD /x 2 P 2 z) effect, with x the parton momentum fraction and Pz the hadron momentum, together with a new O(δ(x)Λ 2 QCD /P 2 z) contribution such that the quark number is conserved. This implies the convergence of the perturbative matching kernel between a quasi-PDF and a PDF would eventually fail for small x. However, in both the R-scheme designed to cancel the leading IR renormalon and the typically used RI/MOM scheme in lattice QCD for the same quasi-PDF, we find good convergence in the kernel based on three-loop bubble-chain diagram analyses. These results are encouraging for the quasi-PDF program. However, firm conclusions can only be drawn after the complete higher loop QCD calculations are carried out.
We construct a 3+1 dimensional holographic model dual to a parity violating hydrodynamic system i... more We construct a 3+1 dimensional holographic model dual to a parity violating hydrodynamic system in 2+1 dimensions. Our model contains gravitational and electrodynamic Chern-Simons terms coupled to a neutral pseudo scalar θ, and a potential composed of quadratic and quartic terms in θ. The background is a charged black brane. We study the hydrodynamics to first order in spacetime derivatives near the probe limit of the pseudo scalar, by extracting the transport coefficients from the scalar, vector, and tensor modes of bulk perturbations. We study two mechanisms for breaking the parity of the boundary fluid: the parity is either spontaneously broken by the nonzero vev of the dual pseudo scalar operator, or by the pseudo scalar source on the boundary. We discover some novel temperaturedependent behaviors of the transport coefficients. It would be interesting to find these behaviors being realized in the real world materials..
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Papers by Jiunn-Wei Chen