Browsing by Author "Yang, Yi"

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A note on on-shell recursion relation of string amplitudes
(2013-02-01)
Chang, Yung-Yeh
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Feng, Bo
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Fu, Chih-Hao
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Lee, Jen-Chi
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Wang, Yihong
In the application of on-shell recursion relation to string amplitudes, one challenge is the sum over infinite intermediate on-shell string states. In this note, we show how to sum these infinite states explicitly by including unphysical states to make complete Fock space.
A refined holographic QCD model and QCD phase structure
(2014-11-26)
Yang, Yi
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Yuan, Pei-Hung
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電子物理學系
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物理研究所
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Department of Electrophysics
We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic gauge function and a dilaton potential. A family of analytic solutions is obtained by the potential reconstruction method. We then study its holographic dual QCD model. After fixing the kinetic gauge function by requesting the linear Regge spectrum of mesons, we calculate the free energy to obtain the phase diagram of the holographic QCD model.
Approaching confinement structure for light quarks in a holographic soft wall QCD model
(2017-09-12)
Li, Meng-Wei
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Yang, Yi
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Yuan, Pei-Hung
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電子物理學系
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物理研究所
We study the confinement-deconfinement phase transition in a holographic soft-wall QCD model. By solving the Einstein-Maxwell-scalar system analytically, we obtain the phase structure of the black hole backgrounds. We then impose probe open strings in such a background to investigate the confinement-deconfinement phase transition from different open string configurations under various temperatures and chemical potentials. Furthermore, we study the Wilson loop by calculating the minimal surface of the probing open string world sheet and obtain the Cornell potential in the confinement phase analytically.
Comments on the high energy limit of bosonic open string theory
(2006-08-14)
Chan, Chuan-Tsung
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Ho, Pei-Ming
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Lee, Jen-Chi
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Teraguchi, Shunsuke
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Yang, Yi
In previous works, ratios among four-point scattering amplitudes at the leading order in the high-energy limit were derived for the bosonic open string theory. The derivation was based on Ward identities derived from the decoupling of zero-norm states and was purely algebraic. The only assumption of the derivation was that the momentum polarization can be approximated by the longitudinal polarization at high energies. In this paper, using the decoupling of spurious states, we reduce this assumption to a much weaker one which can be easily verified by simple power counting in most cases. For the special cases which are less obvious, we verify the new assumption for an example by saddle-point approximation. We also provide a new perspective to our previous results in terms of DDF states. In particular, we show that, by using DDF states, one can easily see that there is only one independent high energy scattering amplitude for each fixed mass level. (c) 2006 Elsevier B.V. All rights reserved.
Confinement-deconfinement phase transition for heavy quarks in a soft wall holographic QCD model
(2015-12-28)
Yang, Yi
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Yuan, Pei-Hung
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電子物理學系
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物理研究所
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Department of Electrophysics
We study confinement-deconfinement phase transition for heavy quarks in a soft wall holographic QCD model. We consider a black hole background in an Einstein-Maxwell- scalar system and add probe open strings to the background. Combining the various configurations of the open strings and the phase structure of the black hole background itself, we obtain the confinement-deconfinement phase diagram for heavy quarks in the holographic QCD model.
Confront holographic QCD with Regge trajectories of vectors and axial-vectors
(2010-03-01)
He, Song
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Huang, Mei
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Yan, Qi-Shu
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Yang, Yi
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電子物理學系
By matching the predictions of the Dp-Dq soft-wall model in type II superstring theory with the spectra of vector and axial-vector mesons, we show the dependence of the Regge trajectories parameters on the metric parameters of the model. From the experimental results of Regge parameters for vector mesons, it is found that the D3 background brane with both q=5 and q=7 probe brane and D4 background brane with q=4 probe brane are close to the realistic holographic QCD. We also discuss how to realize chiral symmetry breaking in the vacuum and asymptotic chiral symmetry restoration in high excitation states. We find that the constant component of the 5-dimension mass square of axial-vector mesons plays an efficient role to realize the chiral symmetry breaking, and a small negative z (4) correction in the 5-dimension mass square is helpful to realize the chiral symmetry restoration in high excitation states.
Exponential Fall-Off Behavior of Regge Scatterings in Compactified Open String Theory
(2012-11-01)
He, Song
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Lee, Jen-Chi
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We calculate massive string scattering amplitudes of compactified open string in the Regge regime. We extract the complete infinite ratios among high-energy amplitudes of different string states in the fixed angle regime from these Regge string scattering amplitudes. The complete ratios calculated by this indirect method include and extend the subset of ratios calculated previously [J. C. Lee and Y. Yang, Nucl. Phys. B 784 (2007), 22; J. C. Lee, T. Takimi and Y. Yang, Nucl. Phys. B 804 (2008), 250] by the more difficult direct fixed angle calculation. In this calculation of compactified open string scattering, we discover a realization of arbitrary real values L in the identity Eq. (4.18), rather than integer value only in all previous high-energy string scattering amplitude calculations. The identity in Eq. (4-18) was explicitly proved recently in [J. C. Lee, C. H. Yan and Y. Yang, SIGMA 8 (2012), 045, arXiv:1012.5225] to link fixed angle and Rogge string scattering amplitudes. In addition, we discover a kinematic regime with stringy highly winding modes, which shows the unusual exponential fall-off behavior in the Regge string scattering. This is complimentary with a kinematic regime discovered previously [J. C. Lee, T. Takimi and Y. Yang, Nucl. Phys. B 804 (2008), 2501 which shows the unusual power-law behavior in the high-energy fixed angle compactified string scatterings.
Extremal RN/CFT in both hands revisited
(2016-04-10)
Kuo, En-Jui
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We study RN/CFT correspondence for four dimensional extremal Reissner-Nordstrom black hole. We uplift the 4d RN black hole to a 5d rotating black hole and make a geometric regularization of the 5d space-time. Both hands central charges are obtained correctly at the same time by Brown-Henneaux technique. (C) 2016 The Authors. Published by Elsevier B.V.
High-energy massive string scatterings from orientifold planes
(2008-07-21)
Lee, Jen-Chi
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We calculate bosonic massive closed string states at arbitrary mass levels scattered from orientifold planes in the high-energy, fixed angle limit. For the case of O-particle scatterings, we obtain infinite linear relations among high-energy scattering amplitudes of different string states. We also confirm that there exist only closed string Regge poles in the form factor of the O-particle amplitudes as expected. For the case of O-domain-wall scatterings, we find that, like the well-known D-instanton scatterings, the amplitudes behave like field theory scatterings, namely UV power-law without infinite Regge poles. In addition, we discover that there exist only finite number of t-channel closed string poles in the form factor of O-domain-wall scatterings, and the masses of the poles are bounded by the masses of the external legs. We thus confirm that all massive closed string states do couple to the O-domain-wall. (c) 2008 Elsevier B.V. All rights reserved.
High-Energy String Scattering Amplitudes and Signless Stirling Number Identity
(2012)
Lee, Jen-Chi
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Yan, Catherine H.
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Yang, Yi
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電子物理學系
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Department of Electrophysics
"We give a complete proof of a set of identities (7) proposed recently from calculation of high-energy string scattering amplitudes. These identities allow one to extract ratios among high-energy string scattering amplitudes in the fixed angle regime from high-energy amplitudes in the Regge regime. The proof is based on a signless Stirling number identity in combinatorial theory. The results are valid for arbitrary real values L rather than only for L = 0,1 proved previously. The identities for non-integer real value L were recently shown to be realized in high-energy compactified string scattering amplitudes [He S., Lee J.C., Yang Y., arXiv:1012.3158]. The parameter L is related to the mass level of an excited string state and can take non-integer values for Kaluza-Klein modes."
High-energy string scatterings of compactified open string
(2008-11-21)
Lee, Jen-Chi
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Takimi, Tomohisa
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We calculate high-energy massive string scattering amplitudes of compactified open string. We derive infinite linear relations, or stringy symmetries, among soft high-energy string scattering amplitudes of different string states in the Gross kinematic regime (GR). In addition, we systematically analyze all hard power-law and soft exponential fall-off regimes of high-energy compactified open string scatterings by comparing the scatterings with their 26D noncompactified counterparts. In particular, we discover the existence of a power-law regime at fixed angle and an exponential fall-off regime at small angle for high-energy compactified open string scatterings. The linear relations break down as expected in all power-law regimes. The analysis can be extended to the high-energy scatterings of the compactified closed string, which corrects and extends the previous results in [J.C. Lee, Y. Yang. Linear relations and their breakdown in high energy massive string scatterings in compact spaces, Nucl. Phys. B 784 (2007) 22]. (C) 2008 Published by Elsevier B.V.
Higher Spin String States Scattered from D-Particle in the Regge Regime and Factorized Ratios of Fixed Angle Scatterings
(2011-09-01)
Lee, Jen-Chi
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Mitsuka, Yoshihiro
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We study scattering of higher spin closed string states at arbitrary mass levels from D-particle in the Regge regime. We extract the complete infinite ratios among high-energy amplitudes of different string states in the fixed angle regime from these Regge string scattering amplitudes. In this calculation, we have used an identity proved recently based on a signless Stirling number identity in combinatorial theory. The complete ratios calculated by this indirect method include a subset of ratios calculated previously by direct fixed angle calculation [C. T. Chan, J. C. Lee and Y. Yang, Nucl. Phys. B 764 (2007), 1]. Moreover, we discover that in spite of the non-factorizability of the closed string D-particle scattering amplitudes, the complete ratios derived for the fixed angle regime are found to be factorized. These ratios are consistent with the decoupling of high-energy zero norm states calculated previously.
Holographic entanglement entropy in boundary conformal field theory
(2018-11-21)
Chang, En-Jui
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Chou, Chia-Jui
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We study the holographic entanglement entropy in a (d + 1)-dimensional boundary quantum field theory at both the zero and finite temperature. The phase diagrams for the holographic entanglement entropy at various temperatures are obtained by solving the entangled surfaces in the different homology. We also verify the Araki-Lieb inequality and illustrate the entanglement plateau.
Holographic superconductors: An analytic method revisit
(2020-03-01)
Chang, En-Jui
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Chou, Chia-Jui
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We study a non-minimal holographic superconductors model in both non-backreaction and full-backreaction cases using an analytic matching method. We calculate the condensate of the dilaton and the critical temperature of the phase transition. We also study the properties of the electric conductivity in various parameters. (C) 2020 The Authors. Published by Elsevier B.V.
Inverse magnetic catalysis in the soft-wall model of AdS/QCD
(2017-02-07)
Li, Danning
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Huang, Mei
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Yang, Yi
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Yuan, Pei-Hung
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電子物理學系
Magnetic effects on chiral phase transition have been investigated in a modified soft-wall AdS/QCD model, in which the dilaton field is taken to be negative at the ultraviolet region and positive at the infrared region as in Phys. Rev. D 93 (2016) 101901 and JHEP 04 (2016) 036. The magnetic field is introduced into the background geometry by solving the Einstein-Maxwell system. After embedding the magnetized background geometry into the modified soft-wall model, the magnetic field dependent behavior of chiral condensate is worked out numerically. It is found that, in the chiral limit, the chiral phase transition remains as a second order at finite magnetic field B, while the symmetry restoration temperature and chiral condensate decrease with the increasing of magnetic field in small B region. When including finite quark mass effect, the phase transition turns to be a crossover one, and the transition temperature still decreases with increasing magnetic field B when B is not very large. In this sense, inverse magnetic catalysis effect is observed in this modified soft-wall AdS/QCD model.
Linear relations and their breakdown in high energy massive string scatterings in compact spaces
(2007-11-12)
Lee, Jen-Chi
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We calculate high energy massive scattering amplitudes of closed bosonic string compactified on the torus. For each fixed mass level with given quantized and winding momenta (m/R ,1/2 nR), we obtain infinite R linear relations among high energy scattering amplitudes of different string states. For some kinematic regimes, we discover that linear relations with N-R = N-L break down and, simultaneously, the amplitudes enhance to power-law behavior instead of the usual exponential fall-off behavior at high energies. It is the space-time T-duality symmetry that plays a role here. This result is consistent with the coexistence of the linear relations and the softer exponential fall-off behavior of high energy string scattering amplitudes as we pointed out previously. It is also reminiscent of our previous work on the power-law behavior of high energy string/domain-wall scatterings. (c) 2007 Elsevier B.V. All rights reserved.
Linear relations of high energy absorption/emission amplitudes of D-brane
(2007-03-08)
Lee, Jen-Chi
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We calculate the absorption amplitudes of a closed string state at arbitrary mass level leading to two open string states on the D-brane at high energies. As in the case of Domain-wall scattering we studied previously, this process contains only one kinematic variable. However, in contrast to the power-law behavior of Domain-wall scattering, its form factor behaves as exponential fall-off in the high energy limit. After identifying the geometric parameter of the kinematic, we derive the linear relations (of the kinematic variable) and ratios among the high energy amplitudes corresponding to absorption of different closed string states for each fixed mass level by D-brane. This result is consistent with the coexistence of the linear relations and exponential fall-off behavior of high energy string/D-brane amplitudes. (c) 2007 Elsevier B.V. All rights reserved.
Massive superstring scatterings in the Regge regime
(2011-03-31)
He, Song
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Lee, Jen-Chi
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Takahashi, Keijiro
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Yang, Yi
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電子物理學系
We calculate four classes of high-energy massive string scattering amplitudes of fermionic string theory at arbitrary mass levels in the Regge regime (RR). We show that all four leading order amplitudes in the RR can be expressed in terms of the Kummer function of the second kind. Based on the summation algorithm of a set of extended signed Stirling number identities, we show that all four ratios calculated previously by the method of decoupling of zero-norm states among scattering amplitudes in the Gross regime can be extracted from this Kummer function in the RR. Finally, we conjecture and give evidence that the existence of these four Gross regime ratios in the RR persists to subleading orders in the Regge expansion of all high-energy fermionic string scattering amplitudes.
Notes on high-energy limit of bosonic closed string scattering amplitudes
(2006-08-14)
Chan, Chuan-Tsung
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Lee, Jen-Chi
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Yang, Yi
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電子物理學系
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Department of Electrophysics
We study bosonic closed string scattering amplitudes in the high-energy limit. We find that the methods of decoupling of high-energy zero-norm states and the high-energy Virasoto constraints, which were adopted in the previous works to calculate the ratios among high-energy open string scattering amplitudes of different string states, persist for the case of closed string. However, we clarify the previous saddle-point calculation for high-energy open string scattering amplitudes and claim that only (t, u) channel of the amplitudes is suitable for saddle-point calculation. We then discuss three evidences to show that saddle-point calculation for high-energy closed string scattering amplitudes is not reliable. By using the relation of tree-level closed and open string scattering amplitudes of Kawai, Lewellen and Tye (KLT), we calculate the high-energy closed string scattering amplitudes for arbitrary mass levels. For the case of high-energy closed string four-tachyon amplitude, our result differs from the previous one of Gross and Mende, which is NOT consistent with KLT formula, by an oscillating factor. (c) 2006 Elsevier B.V. All rights reserved.
Optimal electromechanical control of the excitonic fine structures of droplet epitaxial quantum dots
(2018-10-19)
Cheng, Shun-Jen
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Yang, Yi
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Wu, Yu-Nien
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Liao, Yu-Huai
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Peng, Guan-Hao
The intrinsic fine structure splittings (FSSs) of the exciton states of semiconductor quantum dots (QDs) are known to be the major obstacle for realizing the QD-based entangled photon pair emitters. In this paper, we present a theoretical and computational investigation of the excitonic fine structures of droplet-epitaxial (DE) GaAs/AlGaAs QDs under the electromechanical control of micromachined piezoelectric actuators. From the group theory analysis with numerical confirmation based on the developed exciton theory, we reveal the general principle for the optimal design of micromachined actuators whose application onto an elongated QD can certainly suppress its FSS. We show that the use of two independent tuning stresses is sufficient to achieve the FSS elimination but is not always necessary as widely deemed. The use of a single tuning stress to eliminate the FSS of an elongated QD is possible as long as the crystal structure of the actuator material is in coincidence with that of the QD. As a feasible example, we show that a single symmetric biaxial stress naturally generated from the (001) [Pb(Mg1/3Nb2/3)O-3](0.)(72)-[PbTiO3](0.)(28) (PMN-PT) actuator can be used as a single tuning knob to make the full FSSelimination for elongated DE GaAs QDs.