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Search Results: 1 - 10 of 2159 matches for " Boram Yoon "
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Disconnected Quark Loop Contributions to Nucleon Structure
Tanmoy Bhattacharya,Rajan Gupta,Boram Yoon
Physics , 2015,
Abstract: We calculate the disconnected contribution to isoscalar nucleon charges for scalar, axial and tensor channels of light and strange quarks. The calculation has been done with the Clover valence quarks on the MILC $N_f=2+1+1$ HISQ lattices whose light quark masses corresponding to the pion masses of 305 MeV and 217 MeV at $a \approx 0.12$ fm and 312 MeV at $a \approx 0.09$ fm. All-mode-averaging technique is used for the evaluation two-point functions. Disconnected quark loops are estimated by using the truncated solver method with Gaussian random noise sources. Contamination from the excited states is removed by fitting the results of various source-sink separations and operator insertions to the formula including up to the first excited state, simultaneously.
Taste non-Goldstone, flavor-charged pseudo-Goldstone boson decay constants in staggered chiral perturbation theory
Jon A. Bailey,Weonjong Lee,Boram Yoon
Physics , 2012, DOI: 10.1103/PhysRevD.87.054508
Abstract: We calculate the axial current decay constants of taste non-Goldstone pions and kaons in staggered chiral perturbation theory through next-to-leading order. The results are a simple generalization of the results for the taste Goldstone case. New low-energy couplings are limited to analytic corrections that vanish in the continuum limit; certain coefficients of the chiral logarithms are modified, but they contain no new couplings. We report results for quenched, fully dynamical, and partially quenched cases of interest in the chiral SU(3) and SU(2) theories.
Taste non-Goldstone pion decay constants in staggered chiral perturbation theory
Jon A. Bailey,Boram Yoon,Weonjong Lee
Physics , 2012,
Abstract: We calculate the next-to-leading order axial current decay constants of taste non-Goldstone pions and kaons in staggered chiral perturbation theory. This is an extension of the taste Goldstone decay constants calculation to that of the non-Goldstone tastes. We present results for the partially quenched case in the SU(3) and SU(2) staggered chiral perturbation theories and discuss the difference between the taste Goldstone and non-Goldstone cases.
Non-Perturbative Renormalization for Staggered Fermions (Self-energy Analysis)
Jangho Kim,Boram Yoon,Weonjong Lee
Physics , 2012,
Abstract: We present preliminary results of data analysis for the non-perturbative renormalization (NPR) on the self-energy of the quark propagators calculated using HYP improved staggered fermions on the MILC asqtad lattices. We use the momentum source to generate the quark propagators. In principle, using the vector projection operator of $(\bar{\bar{\gamma_\mu \otimes 1}})$ and the scalar projection operator $(\bar{\bar{1 \otimes 1}})$, we should be able to obtain the wave function renormalization factor $Z_q'$ and the mass renormalization factor $Z_q \cdot Z_m$. Using the MILC coarse lattice, we obtain a preliminary but reasonable estimate of $Z_q'$ and $Z_q \cdot Z_m$ from the data analysis on the self-energy.
Recent progress in staggered chiral perturbation theory
Bailey, Jon;Kim, Hyung-Jin;Lee, Weonjong;Yoon, Boram
High Energy Physics - Phenomenology , 2013,
Abstract: We present a review on recent progress in staggered chiral perturbation theory (SChPT). In the last decade, the scope of the application of SChPT has been extended beyond the level of calibration into the region of prediction with high precision. SChPT becomes an essential tool to do the data analysis reliably for physical observables calculated using improved staggered fermions. Here, we focus on the following examples: pion spectrum, pion decay constants, $\varepsilon_K$, and $\pi-\pi$ scattering amplitudes. In each subject, we review the recent progress and future prospects.
Non-perturbative Renormalization of Bilinear Operators with Improved Staggered Quarks
Jangho Kim,Jongjeong Kim,Weonjong Lee,Boram Yoon
Physics , 2013,
Abstract: We present renormalization factors for the bilinear operators obtained using the non-perturbative renormalization method (NPR) in the RI-MOM scheme with improved staggered fermions on the MILC asqtad lattices ($N_f = 2+1$). We use the MILC coarse ensembles with $20^3 \times 64$ geometry and $am_{\ell}/am_s = 0.01/0.05$. We obtain the wave function renormalization factor $Z_q$ from the conserved vector current and the mass renormalization factor $Z_m$ from the scalar bilinear operator. We also present preliminary results of renormalization factors for other bilinear operators.
Trouble shooting for covariance fitting in highly correlated data
Boram Yoon,Yong-Chull Jang,Weonjong Lee,Chulwoo Jung
Physics , 2011,
Abstract: We report a possible solution to the trouble that the covariance fitting fails when the data is highly correlated and the covariance matrix has small eigenvalues. As an example, we choose the data analysis of highly correlated $B_K$ data on the basis of the SU(2) staggered chiral perturbation theory. Basically, the essence of the problem is that we do not have an accurate fitting function so that we cannot fit the highly correlated and precise data. When some eigenvalues of the covariance matrix are small, even a tiny error of fitting function can produce large chi-square and spoil the fitting procedure. We have applied a number of prescriptions available in the market such as diagonal approximation and cutoff method. In addition, we present a new method, the eigenmode shift method which fine-tunes the fitting function while keeping the covariance matrix untouched.
Recent progress in staggered chiral perturbation theory
Jon Bailey,Hyung-Jin Kim,Weonjong Lee,Boram Yoon
Physics , 2013,
Abstract: We present a review on recent progress in staggered chiral perturbation theory (SChPT). In the last decade, the scope of the application of SChPT has been extended beyond the level of calibration into the region of prediction with high precision. SChPT becomes an essential tool to do the data analysis reliably for physical observables calculated using improved staggered fermions. Here, we focus on the following examples: pion spectrum, pion decay constants, $\varepsilon_K$, and $\pi-\pi$ scattering amplitudes. In each subject, we review the recent progress and future prospects.
Covariance fitting of highly correlated data in lattice QCD
Boram Yoon,Yong-Chull Jang,Chulwoo Jung,Weonjong Lee
Physics , 2011,
Abstract: We address a frequently asked question on the covariance fitting of the highly correlated data such as our $B_K$ data based on the SU(2) staggered chiral perturbation theory. Basically, the essence of the problem is that we do not have an accurate fitting function enough to fit extremely precise data. When eigenvalues of the covariance matrix are small, even a tiny error of fitting function yields large chi-square and spoils the fitting procedure. We have applied a number of prescriptions available in the market such as the cut-off method, modified covariance matrix method, and Bayesian method. We also propose a brand new method, the eigenmode shift method which allows a full covariance fitting without modifying the covariance matrix at all. In our case, the eigenmode shift (ES) method and Bayesian method turn out to be the best prescription to the problem. We also provide a pedagogical example of data analysis in which the diagonal approximation and the cut-off method fail in fitting manifestly, but the ES method and the Bayesian approach work well.
Precision calculations of nucleon charges $g_A$, $g_S$, $g_T$
Rajan Gupta,Tanmoy Bhattacharya,Anosh Joseph,Huey-Wen Lin,Boram Yoon
Physics , 2015,
Abstract: We present a detailed analysis of statistical and systematic errors in the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state. These analyses are being done on dynamical $N_f=2+1+1$ HISQ configurations generated by the MILC Collaboration using valence clover fermions. Using ensembles at three values of the lattice spacing ($a=0.12,\ 0.09,$ and $0.06$ fm) and three values of the quark mass ($M_\pi \approx 310,\ 220$ and $130$ MeV) we find that the estimates of the tensor charge are stable and it can be extracted with $5\%$ precision with O(10,000) measurements. We also find that higher statistics are needed to resolve the various uncertainties in the calculation of $g_A$ and improve the signal in $g_S$, which with present data has large errors. A brief status report on the mixing and renormalization of novel operators contributing to nEDM is also given.
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