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Peng Chen

Publications and source records attributed to Peng Chen.

At least 451 records · Page 25Linked to original sources
arXiv2015

Warped flavor symmetry predictions for neutrino physics

A realistic five-dimensional warped scenario with all standard model fields propagating in the bulk is proposed. Mass hierarchies would in principle be accounted for by judicious choices of the bulk mass parameters, while fermion mixing angles are restricted by a $Δ(27)$ flavor symmetry broken on the branes by flavon fields. The latter gives stringent predictions for the neutrino mixing parameters, and the Dirac CP violation phase, all described in terms of only two independent parameters at leading order. The scheme also gives an adequate CKM fit and should be testable within upcoming oscillation experiments.

hep-ph↗
arXiv2015

Neutrino Mixing from CP Symmetry

The neutrino mass matrix has remnant CP symmetry expressed in terms of the lepton mixing matrix, and vice versa the remnant CP transformations allow us to reconstruct the mixing matrix. We study the scenario that all the four remnant CP transformations are preserved by the neutrino mass matrix. The most general parameterization of remnant CP transformations is presented. The lepton mixing matrix is completely fixed by the remnant CP, and its explicit form is derived. The necessary and sufficient condition for conserved Dirac CP violating phase is found. If the Klein four flavor symmetry generated by the postulated remnant CP transformations arises from a finite flavor symmetry group, the phenomenologically viable lepton flavor mixing would be the trimaximal pattern, both Dirac CP phase $δ_{CP}$ and Majorana phase $α_{31}$ are either $0$ or $π$ while another Majorana phase $α_{21}$ is a rational multiple of $π$. These general results are confirmed to be true in the case that the finite flavor symmetry group is $Δ(6n^2)$.

hep-ph↗
arXiv2015

Frequency-Bin Entanglement with Tunable Phase

We describe a technique to produce narrow-band photon pairs with frequency-bin entanglement, whose relative phase can be tuned using linear polarization optics. We show that, making use of the polarization-frequency coupling effect, the phase of a complex polarizer can be transferred into the frequency entanglement.

quant-ph↗
arXiv2014

Lepton Flavor Mixing and CP Symmetry

The strategy of constraining the lepton flavor mixing from remnant CP symmetry is investigated in a rather general way. The neutrino mass matrix generally admits four remnant CP transformations which can be derived from the measured lepton mixing matrix in the charged lepton diagonal basis. Conversely, the lepton mixing matrix can be reconstructed from the postulated remnant CP transformations. All mixing angles and CP violating phases can be completely determined by the full set of remnant CP transformations or three of them. When one or two remnant CP transformations are preserved, the resulting lepton mixing matrix would depend on three real parameters or one real parameter respectively in addition to the parameters characterizing the remnant CP, and the concrete form of the mixing matrix is presented. The phenomenological predictions for the mixing parameters are discussed. The conditions leading to vanishing or maximal Dirac CP violation are studied.

hep-ph↗
arXiv2014

Narrowband Biphotons with Polarization-Frequency Coupled Hyperentanglement

We demonstrate the generation of narrowband biphotons with polarization-frequency coupled hy- perentanglement from spontaneous four-wave mixing in cold atoms. The coupling between polariza- tion and frequency is realized through a frequency shifter and linear optics. When the polarization- frequency degrees of freedom are decoupled, it is robust to create polarization and frequency Bell states, confirmed by the polarization quantum-state tomography and the two-photon temporal quan- tum beating. Making use of the polarization-frequency coupling to transfer polarization phase retard to the entangled frequency modes, we produce a frequency Bell state with tunable phase difference between its two bases.

quant-ph↗
arXiv2014

Riesz transforms on non-compact manifolds

Let $M$ be a complete non-compact Riemannian manifold satisfying the doubling volume property as well as a Gaussian upper bound for the corresponding heat kernel. We study the boundedness of the Riesz transform $dΔ^{-\frac{1}{2}}$ on both Hardy spaces $H^p$ and Lebesgue spaces $L^p$ under two different conditions on the negative part of the Ricci curvature $R^-$. First we prove that if $R^-$ is $α$-subcritical for some $α\in [0,1)$, then the Riesz transform $d^*Δ^{-\frac{1}{2}}$ on differential $1$-forms is bounded from the associated Hardy space $H^p_{\overrightarrowΔ}(Λ^1T^*M)$ to $L^p(M)$ for all $p\in [1,2]$. As a consequence, the Riesz transform (on functions) is bounded on $ L^p$ for all $p\in (1,p_0)$ where $p_0>2$ depends on $α$ and the constant appearing in the doubling property. Second, we prove that if $$\int_0^1 \left\|\frac{|R^-|^{\frac{1}{2}}}{v(\cdot,\ \sqrt{t})^{\frac{1}{p_1}}}\right\|_{p_1}\frac{dt}{\sqrt{t}}+\int_1^\infty \left\|\frac{|R^-|^{\frac{1}{2}}}{v(\cdot,\ \sqrt{t})^{\frac{1}{p_2}}}\right\|_{p_2}\frac{dt}{\sqrt{t}}<\infty,$$ for some $p_1>2$ and $p_2>3$, then the Riesz transform $dΔ^{-\frac{1}{2}}$ is bounded on $L^p$ for all $1 0$, then $dΔ^{-\frac{1}{2}}$ is bounded on $L^p$ for all $1 2$ under conditions on $R^-$ and the potential $V$. We prove both positive and negative results on the boundedness of $dA^{-\frac{1}{2}}$ on $L^p$

math.AP↗
arXiv2014

High-Curie-temperature ferrimagnetism and ferroelectricity in Bi2FeMoO6

BiFeO3 is the most famous multiferroic material, but its G-type antiferromagnetism is highly desirable to be replaced by strong macroscopic magnetism beyond room temperature. Here we obtain double perovskite Bi2FeMoO6 with R3 (#146) space group by substituting Mo for 50% Fe in BiFeO3. Our first-principles calculated results show that it is a semiconductor with gap reaching to 0.725 eV, its net magnetic moment is 2μ_B per formula unit, and its ferroelectric polarization is 85μC/cm^2. This ferroelctricity is comparable with that of BiFeO3, but here the magnetism is a strong ferrimagnetism with Curie temperature of 650 K. Our first-principles phonon spectra establishes that this R3 phase is stable. Electric polarization and magnetic easy axis are shown to be in pseudo-cubic [111] axis. Our further analysis shows that the multiferroic mechanism is similar to that in BiFeO3. Therefore, this Bi2FeMoO6 can be used to achieve strong macroscopic magnetism and ferroelectricity well above room temperature, being useful for designing new multifunctional materials and devices.

cond-mat.mtrl-sci↗
arXiv2014

Temporal Quantum-State Tomography of Narrowband Biphotons

We describe and demonstrate a quantum state tomography for measuring the complex temporal waveform of narrowband biphotons. Through six sets of two-photon interference measurements projected in different polarization subspaces, we can construct the time-frequency entangled two-photon joint amplitude and phase functions in continuous-variable time domain. For the first time, we apply this technique to experimentally determine the temporal quantum states of narrowband biphotons generated from spontaneous four-wave mixing in cold atoms, and fully confirm the theoretical predictions.

quant-ph↗
arXiv2014

Bochner-Riesz profile of anharmonic oscillator ${\mathcal L}=-\frac{d^2}{dx^2}+|x|$

We investigate spectral multipliers, Bochner-Riesz means and convergence of eigenfunction expansion corresponding to the Schrödinger operator with anharmonic potential ${\mathcal L}=-\frac{d^2}{dx^2}+|x|$. We show that the Bochner-Riesz profile of the operator ${\mathcal L}$ completely coincides with such profile of the harmonic oscillator ${\mathcal H}=-\frac{d^2}{dx^2}+x^2$. It is especially surprising because the Bochner-Riesz profile for the one-dimensional standard Laplace operator is known to be essentially different and the case of operators ${\mathcal H}$ and ${\mathcal L}$ resembles more the profile of multidimensional Laplace operators. Another surprising element of the main obtained result is the fact that the proof is not based on restriction type estimates and instead entirely new perspective have to be developed to obtain the critical exponent for Bochner-Riesz means convergence.

math.AP↗
arXiv2014

Re-t2g-splitting-driven semiconductor gaps in ferrimagnetic double perovskite Ca2MReO6 (M=Cr,Fe) from first principles

Motivated by the observation of nonmetallic nature in double perovskite Ca2CrReO6 and Ca2FeReO6 with high magnetic Curie temperatures of 360 and 522 K, we systematically investigate the structural, electronic, and magnetic properties of Ca2MReO6 (M=Cr,Fe) using the full-potential linear augmented plane wave (FP-LAPW) method within the density functional theory. Our full optimization confirms the stable ground-state structure with $P2_1/n$ symmetry. The modified Becke-Johnson (mBJ) exchange potential is used for investigating electronic structures. Our mBJ calculation shows that they are both ferrimagnetic semiconductors with semiconductor gaps of 0.38 eV and 0.05 eV, respectively, in contrast with wrong metallic phases from the generalized gradient approximation (GGA). The origin of semiconductor gap is due to the further distortion of ReO$_6$ octahedra caused by John-Teller effect, which drives the three partially-occupied Re $t_{2g}$ bands split into two fully-filled bands and one empty band in the minority-spin channel. With the spin-orbit coupling (SOC) taken into account, the Ca2MReO6 (M=Cr,Fe) shows high magneto-crystalline anisotropy (MCA) with the magnetic easy axis along pseudocubic [010] direction, and the total magnetic moments increase by 0.209$μ_B$ and 0.258$μ_B$ per formula unit, respectively, due to the strong SOC effect on Re ion. Although reducing to 0.31 and 0.03 eV, the semiconductor gaps remain open in spite of the SOC broadening of the Re $t_{2g}$-related bands. Therefore, our DFT investigation with mBJ has established the correct ferrimagnetic semiconductor ground state for the double perovskites Ca2MReO6 (M=Cr,Fe). This mechanism, different from that in double perovskite Sr2CrOsO6, can help understand physical properties of other similar compounds.

cond-mat.mtrl-sci↗
arXiv2013

Performance of Titanium-Oxide/Polymer Insulation in Bi-2212/Ag-alloy Round Wire Wound Superconducting Coils

Conductor insulation is one of the key components needed to make Ag-alloy clad Bi2Sr2CaCu2O8+x (Bi-2212/Ag) superconducting round wire (RW) successful for high field magnet applications as dielectric standoff and high winding current densities (Jw) directly depend on it. In this study, a TiO2/polymer insulation coating developed by nGimat LLC was applied to test samples and a high field test coil. The insulation was investigated by differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), dielectric properties measurement, and transport critical current (Ic) properties measurement. About 29% of the insulation by weight is polymer. When the Bi-2212/Ag wire is full heat treated, this decomposes with slow heating to 400°C in pure O2. After the full reaction, we found that the TiO2 did not degrade the critical current properties, adhered well to the conductor, and provided a breakdown voltage of >100 V, which allowed the test coil to survive quenching in 31.2 T background field, while providing a 2.6 T field increment. For Bi-2212/Ag RW with a typical diameter of 1.0-1.5 mm, this ~15 um thick insulation allows a very high coil packing factor of ~0.74, whereas earlier alumino-silicate braid insulation only allows packing factors of 0.38-0.48.

cond-mat.supr-con↗
arXiv2012

Sharp spectral multipliers for Hardy spaces associated to non-negative self-adjoint operators satisfying Davies-Gaffney estimates

We consider the abstract non-negative self-adjoint operator $L$ acting on $L^2(X)$ which satisfies Davies-Gaffney estimates and the corresponding Hardy spaces $H^p_L(X)$. We assume that doubling condition holds for the metric measure space $X$. We show that a sharp Hörmander-type spectral multiplier theorem on $H^p_L(X)$ follows from restriction type estimates and the Davies-Gaffney estimates. We also describe the sharp result for the boundedness of Bochner-Riesz means on $H^p_L(X)$.

math.AP↗
arXiv2012

Promising ferrimagnetic double perovskite oxides towards high spin polarization at high temperature

We predict through our first-principles calculations that four double perovskite oxides of Bi2ABO6 (AB = FeMo, MnMo, MnOs, CrOs) are half-metallic ferrimagnets. Our calculated results shows that the four optimized structures have negative formation energy, from -0.42 to -0.26 eV per formula unit, which implies that they could probably be realized. In the case of Bi2FeMoO6, the half-metallic gap and Curie temperature are predicted to reach to 0.71 eV and 650 K, respectively, which indicates that high spin polarization could be kept at high temperatures far beyond room temperature. It is believed that some of them could be synthesized soon and would prove useful for spintronic applications.

cond-mat.mtrl-sci↗
arXiv2012

Restriction estimates, sharp spectral multipliers and endpoint estimates for Bochner-Riesz means

We consider abstract non-negative self-adjoint operators on $L^2(X)$ which satisfy the finite speed propagation property for the corresponding wave equation. For such operators we introduce a restriction type condition which in the case of the standard Laplace operator is equivalent to $(p,2)$ restriction estimate of Stein and Tomas. Next we show that in the considered abstract setting our restriction type condition implies sharp spectral multipliers and endpoint estimates for the Bochner-Riesz summability. We also observe that this restriction estimate holds for operators satisfying dispersive or Strichartz estimates. We obtain new spectral multiplier results for several second order differential operators and recover some known results. Our examples include Schrödinger operators with inverse square potentials on $\RR^n$, the harmonic oscillator, elliptic operators on compact manifolds and Schrödinger operators on asymptotically conic manifolds.

math.AP↗
arXiv2011

Thermodynamic Geometry of the Born-Infeld-anti-de Sitter black holes

Thermodynamic geometry is applied to the Born-Infeld-anti-de Sitter black hole (BIAdS) in the four dimensions, which is a nonlinear generalization of the Reissner-NorstrÄom-AdS black hole (RNAdS). We compute the Weinhold as well as the Ruppeiner scalar curvature and find that the singular points are not the same with the ones obtained using the heat capacity. Legendre-invariant metric proposed by Quevedo and the metric obtained by using the free energy as the thermodynamic potential are obtained and the corresponding scalar curvatures diverge at the Davies points.

gr-qc↗
arXiv2010

Strain Stiffening Induced by Molecular Motors in Active Crosslinked Biopolymer Networks

We have studied the elastic response of actin networks with both compliant and rigid crosslinks by modeling molecular motors as force dipoles. Our finite element simulations show that for compliant crosslinkers such as filamin A, the network can be stiffened by two orders of magnitude while stiffening achieved with incompliant linkers such as scruin is significantly smaller, typically a factor of two, in excellent agreement with recent experiments. We show that the differences arise from the fact that the motors are able to stretch the compliant crosslinks to the fullest possible extent, which in turn causes to the deformation of the filaments. With increasing applied strain, the filaments further deform leading to a stiffened elastic response. When the crosslinks are incompliant, the contractile forces due to motors do not alter the network morphology in a significant manner and hence only small stiffening is observed.

cond-mat.soft↗