余洪伟
主要致力于经典和量子引力理论，量子场论等方面的研究工作
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 姓名：余洪伟
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学术头衔：
博士生导师
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学科领域：
力学
 研究兴趣：主要致力于经典和量子引力理论，量子场论等方面的研究工作
余洪伟，男，美国Tufts大学博士（Ph.D.）, 现任湖南师范大学理论物理专业博士生导师，中国引力与相对论天体物理学会理事, 教育部高校物理学类专业教学指导委员会委员。先后入选教育部新世纪优秀人才支持计划，湖南省首批跨世纪学术与技术带头人培养对象，湖南省高等学校学科带头人。主要致力于经典和量子引力理论，量子场论等方面的研究工作。多次前往欧美国家访问研究，其中在美国Tufts 大学 Tufts Institute of Cosmology 工作、学习五年， 在此期间曾为Tufts大学学生讲授《General Physics》、《The concepts of the cosmos》等课程。先后主持五项国家自然科学基金及教育部门回国留学人员基金、湖南省优秀中青年基金等项目，并参加国家973项目及美国国家自然科学基金资助项目的研究。在国际国内一流学术刊物如：Phys. Rev. D, Nucl. Phys. B, Phys. Lett. B., Phys. Rev. A.,JHEP,《中国科学》等上发表SCI收录论文八十余篇。建立了一套在量子引力框架中研究光锥涨落的方法。该方法已被同行认为是国际上三个有代表性的理论之一 ，著名学者欧洲核子研究中心理论部J. Ellis教授评价其工作是“开创性的（Pioneering）”，所取得的结果是“令人鼓舞的（Encouraging）”；在国际上率先对场的量子涨落驱动的布朗运动进行研究；在黑洞非阿贝尔荷问题上取得的成果，曾荣获1991年度国际研究基金荣誉奖（美国)。 2008年获湖南省科技进步一等奖（第一完成人），全国百篇优秀博士学位论文（指导教师）。

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【期刊论文】Spontaneous absorption of an accelerated hydrogen atom near a conducting plane in vacuum
余洪伟
，0001，（）：
1年11月30日
We study, in the multipolar coupling scheme, a uniformly accelerated multilevel hydrogen atom in interaction with the quantum electromagnetic field near a conducting boundary and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy. It is found that the perfect balance between the contributions of vacuum fluctuations and radiation reaction that ensures the stability of groundstate atoms is disturbed, making spontaneous transition of groundstate atoms to excited states possible in a vacuum with a conducting boundary. The boundaryinduced contribution is effectively a nonthermal correction, which enhances or weakens the nonthermal effect already present in the unbounded case, thus possibly making the effect easier to observe. An interesting feature worth noting is that the nonthermal corrections may vanish for atoms on some particular trajectories.

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余洪伟
，0001，（）：
1年11月30日
We consider a multilevel hydrogen atom in interaction with the quantum electromagnetic field and separately calculate the contributions of the vacuum fluctuation and radiation reaction to the rate of change of the mean atomic energy of the atom for uniform acceleration. It is found that the acceleration disturbs the vacuum fluctuations in such a way that the delicate balance between the contributions of vacuum fluctuation and radiation reaction that exists for inertial atoms is broken, so that the transitions to higherlying states from ground state are possible even in vacuum. In contrast to the case of an atom interacting with a scalar field, the contributions of both electromagnetic vacuum fluctuations and radiation reaction to the spontaneous emission rate are affected by the acceleration, and furthermore the contribution of the vacuum fluctuations contains a nonthermal accelerationdependent correction, which is possibly observable.

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余洪伟
，0001，（）：
1年11月30日
We examine the entanglement creation between two mutually independent twolevel atoms immersed in a thermal bath of quantum scalar fields in the presence of a perfectly reflecting plane boundary. With the help of the master equation that describes the evolution in time of the atom subsystem obtained, in the weakcoupling limit, by tracing over environment scalar fields degrees of freedom, we find that the presence of the boundary may play a significant role in the entanglement creation in some circumstances and the new parameter, the distance of the atoms from the boundary, besides the bath temperature and the separation between the atoms, gives us more freedom in manipulating entanglement generation. Remarkably, the final remaining entanglement in the equilibrium state is independent of the presence of the boundary.

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【期刊论文】Spontaneous excitation of an accelerated atom in a spacetime with a reflecting plane boundary
余洪伟
，0001，（）：
1年11月30日
We study a twolevel atom in interaction with a real massless scalar quantum field in a spacetime with a reflecting boundary. The presence of the boundary modifies the quantum fluctuations of the scalar field, which in turn modifies the radiative properties of atoms. We calculate the rate of change of the mean atomic energy of the atom for both inertial motion and uniform acceleration. It is found that the modifications induced by the presence of a boundary make the spontaneous radiation rate of an excited inertial atom oscillate near the boundary and this oscillatory behavior may offer a possible opportunity for experimental tests for geometrical (boundary) effects in flat spacetime. While for accelerated atoms, the transitions from ground states to excited states are found to be possible even in a vacuum due to changes in the vacuum fluctuations induced by both the presence of the boundary and the acceleration of atoms, and this can be regarded as an actual physical process underlying the Unruh effect.

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【期刊论文】Avoidance of big rip in phantom cosmology by gravitational back reaction
余洪伟
，0001，（）：
1年11月30日
The effects of the gravitational back reaction of cosmological perturbations are investigated in a cosmological model where the universe is dominated by phantom energy. We assume a COBE normalized spectrum of cosmological fluctuations at the present time and calculate the effective energy–momentum tensor of the gravitational backreactions of cosmological perturbations whose wavelengths at the time when the backreactions are evaluated are larger than the Hubble radius. Our results reveal that the effects of gravitational backreactions will counteract that of phantom energy sooner or later and can become large enough to terminate the phantom dominated phase before the big rip as the universe evolves. This arises because the phase space of infrared modes grows very rapidly as we come close to the big rip.

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【期刊论文】Brownian motion of a charged test particle near a reflecting boundary at finite temperature
余洪伟
，0001，（）：
1年11月30日
We discuss the random motion of charged test particles driven by quantum electromagnetic fluctuations at finite temperature in both the unbounded flat space and flat spacetime with a reflecting boundary and calculate the mean squared fluctuations in the velocity and position of the test particle. We show that typically the random motion driven by the quantum fluctuations is one order of magnitude less significant than that driven by thermal noise in the unbounded flat space. However, in the flat space with a reflecting plane boundary, the random motion of quantum origin can become much more significant than that of thermal origin at very low temperature.

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【期刊论文】Brownian motion of a charged test particle in vacuum between two conducting plates
余洪伟， Hongwei Yu， Jun Chen
PHYSICAL REVIEW D 70, 125006 (2004)，0001，（）：
1年11月30日
The Brownian motion of a charged test particle caused by quantum electromagnetic vacuum fluctuations between two perfectly conducting plates is examined and the mean squared fluctuations in the velocity and position of the test particle are calculated. Our results show that the Brownian motion in the direction normal to the plates is reinforced in comparison to that in the single plate case. The effective temperature associated with this normal Brownian motion could be three times as large as that in the single plate case. However, the negative dispersions for the velocity and position in the longitudinal directions, which could be interpreted as reducing the quantum uncertainties of the particle, acquire positive corrections due to the presence of the second plate, and are thus weakened.

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【期刊论文】Vacuumfluctuations and Brownian motion of a charged test particle near a reflecting boundary
余洪伟， Hongwei Yu†， L. H. Ford‡
PHYSICAL REVIEW D, VOLUME 70, 065009，0001，（）：
1年11月30日
We study the Brownian motion of a charged test particle coupled to electromagnetic vacuum fluctuations near a perfectly reflecting plane boundary. The presence of the boundary modifies the quantum fluctuations of the electric field, which in turn modifies the motion of the test particle. We calculate the resulting mean squared fluctuations in the velocity and position of the test particle. In the case of directions transverse to the boundary, the results are negative. This can be interpreted as reducing the quantum uncertainty which would otherwise be present.

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【期刊论文】Quantum inequalities for the free RaritaSchwinger fields in flat spacetime
余洪伟， Hongwei Yu， Puxun Wu
PHYSICAL REVIEW D 69, 064008 (2004)，0001，（）：
1年11月30日
Using the methods developed by Fewster and colleagues, we derive a quantum inequality for the free massive spin 3 2 RaritaSchwinger fields in four dimensional Minkowski spacetime. Our quantum inequality bound for the RaritaSchwinger fields is weaker, by a factor of 2, than that for the spin 1 2 Dirac fields. This fact along with other quantum inequalities obtained by various other authors for the fields of integer spin (bosonic fields) using similar methods lead us to conjecture that, in flat spacetime, separately for bosonic and fermionic fields, the quantum inequality bound gets weaker as the number of degrees of freedom of the field increases. A plausible physical reason might be that the more field degrees of freedom, the more freedom one has to create negative energy, therefore the weaker the quantum inequality bound.

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余洪伟， Hongwei Yu and PuXun Wu
PHYSICAL REVIEW D 68, 084019 (2003)，0001，（）：
1年11月30日
Quantum fluctuations of the light cone are examined in a fourdimensional spacetime with two parallel planes. Both the Dirichlet and the Neumann boundary conditions are considered. In all the cases we have studied, quantum light cone fluctuations are greater where the Neumann boundary conditions are imposed, suggesting that quantum light cone fluctuations depend not only on the geometry and topology of the spacetime as has been argued elsewhere but also on boundary conditions. Our results also show that quantum light cone fluctuations are larger here than that in the case of a single plane. Therefore the confinement of gravitons in a smaller region by the presence of a second plane reinforces the quantum fluctuations and this can be understood as a consequence of the uncertainty principle.

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