arXiv subjects

C. Miao

Publications and source records attributed to C. Miao.

17 recordsLinked to original sources

arXiv2024

Statistical analysis of pulsar flux density distribution

This study presents a comprehensive analysis of the spectral properties of 886 pulsars across a wide frequency range from 20MHz to 343.5GHz, including a total of 86 millisecond pulsars. The majority of the pulsars exhibit power-law behavior in their spectra, although some exceptions are observed. Five different spectral models, namely simple power-law, broken power-law, low-frequency turn-over, high-frequency cut-off, and double turn-over, were employed to explore the spectral behaviors. The average spectral index for pulsars modeled with a simple power-law is found to be -1.64 +/-0.80, consistent with previous studies. Additionally, significant correlations between the spectral index and characteristic parameters are observed particularly in millisecond pulsars, while no strong correlation is observed in normal pulsars. Different models show variations in the most influential characteristic parameters associated with the spectral index, indicating diverse dominant radiation mechanisms in millisecond pulsars.Finally, this study identifies 22 pulsars of the Gigahertz-peaked Spectra (GPS) type for the first time based on the Akaike information criterion.

astro-ph.HE↗

arXiv2016

Sobolev spaces adapted to the Schrödinger operator with inverse-square potential

We study the $L^p$-theory for the Schrödinger operator $\mathcal L_a$ with inverse-square potential $a|x|^{-2}$. Our main result describes when $L^p$-based Sobolev spaces defined in terms of the operator $(\mathcal L_a)^{s/2}$ agree with those defined via $(-Δ)^{s/2}$. We consider all regularities $0<s<2$. In order to make the paper self-contained, we also review (with proofs) multiplier theorems, Littlewood-Paley theory, and Hardy-type inequalities associated to the operator $\mathcal L_a$.

math.AP↗

arXiv2015

The energy-critical NLS with inverse-square potential

We consider the defocusing energy-critical nonlinear Schrödinger equation with inverse-square potential $iu_t = -Δu + a|x|^{-2}u + |u|^4u$ in three space dimensions. We prove global well-posedness and scattering for $a>-\frac14 +\frac1{25}$. We also carry out the variational analysis needed to treat the focusing case.

math.AP↗

arXiv2013

Quark number susceptibilities at high temperatures

We calculate second and fourth order quark number susceptibilities for 2+1 flavor QCD in the high temperature region. In our study we use two improved staggered fermion formulations, namely the highly improved staggered quark formulation, and the so-called p4 formulation, as well as several lattice spacings. Second order quark number susceptibilities are calculated using both improved staggered fermion formulations, and we show that in the continuum limit the two formulations give consistent results. The fourth order quark number susceptibilities are studied only using the p4 formulation and at non-zero lattice spacings. We compare our results on quark number susceptibilities with recent weak coupling calculations, and find that these agree reasonably well with the lattice calculations within the estimated uncertainties.

hep-lat↗

arXiv2011

Global regularity for the supercritical dissipative quasi-geostrophic equation with large dispersive forcing

We consider the 2D quasi-geostrophic equation with supercritical dissipation and dispersive forcing in the whole space. When the dispersive amplitude parameter is large enough, we prove the global well-posedness of strong solution to the equation with large initial data. We also show the strong convergence result as the amplitude parameter goes to $\infty$. Both results rely on the Strichartz-type estimates for the corresponding linear equation.

math.AP↗

arXiv2011

Meson screening masses from lattice QCD with two light and the strange quark

We present results for screening masses of mesons built from light and strange quarks in the temperature range of approximately between 140 MeV to 800 MeV. The lattice computations were performed with 2+1 dynamical light and strange flavors of improved (p4) staggered fermions along a line of constant physics defined by a pion mass of about 220 MeV and a kaon mass of 500 MeV. The lattices had temporal extents Nt = 4, 6 and 8 and aspect ratios of Ns / Nt \geq 4. At least up to a temperature of 140 MeV the pseudo-scalar screening mass remains almost equal to the corresponding zero temperature pseudo-scalar (pole) mass. At temperatures around 3Tc (Tc being the transition temperature) the continuum extrapolated pseudo-scalar screening mass approaches very close to the free continuum result of 2 πT from below. On the other hand, at high temperatures the vector screening mass turns out to be larger than the free continuum value of 2 πT. The pseudo-scalar and the vector screening masses do not become degenerate even for a temperature as high as 4Tc. Using these mesonic spatial correlation functions we have also investigated the restoration of chiral symmetry and the effective restoration of the axial symmetry. We have found that the vector and the axial-vector screening correlators become degenerate, indicating chiral symmetry restoration, at a temperature which is consistent with the QCD transition temperature obtained in previous studies. On the other hand, the pseudo-scalar and the scalar screening correlators become degenerate only at temperatures larger than 1.3Tc, indicating that the effective restoration of the axial symmetry takes place at a temperature larger than the QCD transition temperature.

hep-lat↗

arXiv2010

Quarkonium spectral functions with complex potential

We study quarkonium spectral functions at high temperatures using potential model with complex potential. The real part of the potential is constrained by the lattice QCD data on static quark anti-quark correlation functions, while the imaginary part of the potential is taken from perturbative calculations. We find that the imaginary part of the potential has significant effect on quarkonium spectral functions, in particular, it leas to the dissolution of the 1S charmonium and excited bottomonium states at temperatures about 250 MeV and melting of the ground state bottomonium at temperatures slightly above 450 MeV.

hep-ph↗

arXiv2010

The phase boundary for the chiral transition in (2+1)-flavor QCD at small values of the chemical potential

We determine the chiral phase transition line in (2+1)-flavor QCD for small values of the light quark chemical potential. We show that for small values of the chemical potential the curvature of the phase transition line can be deduced from an analysis of scaling properties of the chiral condensate and its susceptibilities. To do so we extend earlier studies of the magnetic equation of state in (2+1)-flavor QCD to finer lattice spacings, aT=1/8. We use these universal scaling properties of the chiral order parameter to extract the curvature of the transition line at two values of the cut-off, aT=1/4 and 1/8. We find that cut-off effects are small for the curvature parameter and determine the transition line in the chiral limit to leading order in the light quark chemical potential. We obtain Tc(μ_q)/Tc(0) = 1 - 0.059(2)(4) (μ_q/T)^2 +O(μ_q^4).

hep-lat↗

arXiv2010

Equation of State for physical quark masses

We calculate the QCD equation of state for temperatures corresponding to the transition region with physical mass values for two degenerate light quark flavors and a strange quark using an improved staggered fermion action (p4-action) on lattices with temporal extent N_tau=8. We compare our results with previous calculations performed at twice larger values of the light quark masses as well as with results obtained from a resonance gas model calculation. We also discuss the deconfining and chiral aspects of the QCD transition in terms of renormalized Polyakov loop, strangeness fluctuations and subtracted chiral condensate. We show that compared to the calculations performed at twice larger value of the light quark mass the transition region shifts by about 5 MeV toward smaller temperatures

hep-lat↗

arXiv2009

Higher moments of charge fluctuations in QCD at high temperature

We present lattice results for baryon number, strangeness and electric charge fluctuations as well as their correlations at finite temperature and vanishing chemical potentials, i.e. under conditions relevant for RHIC and LHC. We find that the fluctuations change rapidly at the transition temperature $T_c$ and approach the ideal quark gas limit already at approximately $1.5T_c$. This indicates that quarks are the relevant degrees of freedom that carry the quantum numbers of conserved charges at $T\geq 1.5T_c$. At low temperature, qualitative features of the lattice results are well described by a hadron resonance gas model.

hep-lat↗

arXiv2009

On the magnetic equation of state in (2+1)-flavor QCD

A first study of critical behavior in the vicinity of the chiral phase transition of (2+1)-flavor QCD is presented. We analyze the quark mass and volume dependence of the chiral condensate and chiral susceptibilities in QCD with two degenerate light quark masses and a strange quark. The strange quark mass (m_s) is chosen close to its physical value; the two degenerate light quark masses (m_l) are varied in a wide range 1/80 \le m_l/m_s \le 2/5, where the smallest light quark mass value corresponds to a pseudo-scalar Goldstone mass of about 75 MeV. All calculations are performed with staggered fermions on lattices with temporal extent Nt=4. We show that numerical results are consistent with O(N) scaling in the chiral limit. We find that in the region of physical light quark mass values, m_l/m_s \simeq 1/20, the temperature and quark mass dependence of the chiral condensate is already dominated by universal properties of QCD that are encoded in the scaling function for the chiral order parameter, the magnetic equation of state. We also provide evidence for the influence of thermal fluctuations of Goldstone modes on the chiral condensate at finite temperature. At temperatures below, but close to the chiral phase transition at vanishing quark mass, this leads to a characteristic dependence of the light quark chiral condensate on the square root of the light quark mass.

hep-lat↗

arXiv2009

Baryon Number, Strangeness and Electric Charge Fluctuations in QCD at High Temperature

We analyze baryon number, strangeness and electric charge fluctuations as well as their correlations in QCD at high temperature. We present results obtained from lattice calculations performed with an improved staggered fermion action (p4-action) at two values of the lattice cut-off with almost physical up and down quark masses and a physical value for the strange quark mass. We compare these results, with an ideal quark gas at high temperature and a hadron resonance gas model at low temperature. We find that fluctuations and correlations are well described by the former already for temperatures about 1.5 times the transition temperature. At low temperature qualitative features of the lattice results are quite well described by a hadron resonance gas model. Higher order cumulants, which become increasingly sensitive to the light pions, however show deviations from a resonance gas in the vicinity of the transition temperature.

hep-lat↗

arXiv2009

Equation of state and QCD transition at finite temperature

We calculate the equation of state in 2+1 flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent Nt=8. Calculations have been performed with two different improved staggered fermion actions, the asqtad and p4 actions. Overall, we find good agreement between results obtained with these two O(a^2) improved staggered fermion discretization schemes. A comparison with earlier calculations on coarser lattices is performed to quantify systematic errors in current studies of the equation of state. We also present results for observables that are sensitive to deconfining and chiral aspects of the QCD transition on Nt=6 and 8 lattices. We find that deconfinement and chiral symmetry restoration happen in the same narrow temperature interval. In an Appendix we present a simple parametrization of the equation of state that can easily be used in hydrodynamic model calculations. In this parametrization we also incorporated an estimate of current uncertainties in the lattice calculations which arise from cutoff and quark mass effects. We estimate these systematic effects to be about 10 MeV

hep-lat↗

arXiv2008

The Spatial String Tension and Dimensional Reduction in QCD

We calculate the spatial string tension in (2+1) flavor QCD with physical strange quark mass and almost physical light quark masses using lattices with temporal extent N_tau=4,6 and 8. We compare our results on the spatial string tension with predictions of dimensionally reduced QCD. This suggests that also in the presence of light dynamical quarks dimensional reduction works well down to temperatures 1.5T_c.

hep-lat↗

arXiv2008

The QCD Equation of State with almost Physical Quark Masses

We present results on the equation of state in QCD with two light quark flavors and a heavier strange quark. Calculations with improved staggered fermions have been performed on lattices with temporal extent Nt =4 and 6 on a line of constant physics with almost physical quark mass values; the pion mass is about 220 MeV, and the strange quark mass is adjusted to its physical value. High statistics results on large lattices are obtained for bulk thermodynamic observables, i.e. pressure, energy and entropy density, at vanishing quark chemical potential for a wide range of temperatures, 140 MeV < T < 800 MeV. We present a detailed discussion of finite cut-off effects which become particularly significant for temperatures larger than about twice the transition temperature. At these high temperatures we also performed calculations of the trace anomaly on lattices with temporal extent Nt=8. Furthermore, we have performed an extensive analysis of zero temperature observables including the light and strange quark condensates and the static quark potential at zero temperature. These are used to set the temperature scale for thermodynamic observables and to calculate renormalized observables that are sensitive to deconfinement and chiral symmetry restoration and become order parameters in the infinite and zero quark mass limits, respectively.

hep-lat↗

arXiv2006

Study of the finite temperature transition in 3-flavor QCD using the R and RHMC algorithms

We study the finite temperature transition in QCD with three flavors of equal masses using the R and RHMC algorithm on lattices with temporal extent N_τ=4 and 6. For the transition temperature in the continuum limit we find r_0 T_c=0.429(8) for the light pseudo-scalar mass corresponding to the end point of the 1st order transition region. When comparing the results obtained with the R and RHMC algorithms for p4fat3 action we see no significant step-size errors down to a lightest pseudo-scalar mass of m_{ps} r_0=0.4.

hep-lat↗

arXiv2006

The transition temperature in QCD

We present a detailed calculation of the transition temperature in QCD with two light and one heavier (strange) quark mass on lattices with temporal extent N_t =4 and 6. Calculations with improved staggered fermions have been performed for various light to strange quark mass ratios in the range, 0.05 <= m_l/m_s <= 0.5, and with a strange quark mass fixed close to its physical value. From a combined extrapolation to the chiral (m_l -> 0) and continuum (aT = 1/N_t -> 0) limits we find for the transition temperature at the physical point T_c r_0 = 0.457(7) where the scale is set by the Sommer-scale parameter r_0 defined as the distance in the static quark potential at which the slope takes on the value, (dV_qq(r)/dr)_r=r_0 = 1.65/r_0^2. Using the currently best known value for r_0 this translates to a transition temperature T_c = 192(7)(4)MeV. The transition temperature in the chiral limit is about 3% smaller. We discuss current ambiguities in the determination of T_c in physical units and also comment on the universal scaling behavior of thermodynamic quantities in the chiral limit.

hep-lat↗