To solve the cosmological constant fine tuning problem,we investigate an(n+1)-dimensional generalized Randall-Sundrum brane world scenario with two(n−1)-branes instead of two 3-branes.Adopting an anisotropic metric an...To solve the cosmological constant fine tuning problem,we investigate an(n+1)-dimensional generalized Randall-Sundrum brane world scenario with two(n−1)-branes instead of two 3-branes.Adopting an anisotropic metric ansatz,we obtain the positive effective cosmological constantΩeff of order 10−124 and only require a solution≃50−80.Meanwhile,both the visible and hidden branes are stable because their tensions are positive.Therefore,the fine tuning problem can be solved quite well.Furthermore,the Hubble parameter H1(z)as a function of redshift z is in good agreement with the cosmic chronometers dataset.The evolution of the universe naturally shifts from deceleration to acceleration.This suggests that the evolution of the universe is intrinsically an extra-dimensional phenomenon.It can be regarded as a dynamic model of dark energy that is driven by the evolution of the extra dimensions on the brane.展开更多
We investigate an(n+1)-dimensional generalized Randall-Sundrum model with an anisotropic metric which has three different scale factors.One obtains a positive effective cosmological constant Ωeff∼10^−124(in Planck u...We investigate an(n+1)-dimensional generalized Randall-Sundrum model with an anisotropic metric which has three different scale factors.One obtains a positive effective cosmological constant Ωeff∼10^−124(in Planck units),which only needs a solution kr≃50−80 without fine tuning.Both the visible and hidden brane tensions are positive,which renders the two branes stable.Then,we find that the Hubble parameter is close to a constant in a large region near its minimum,thus causing the acceleration of the universe.Meanwhile,the scale of extra dimensions is smaller than the observed scale but greater than the Planck length.This may suggest that the observed present acceleration of the universe is caused by the extra-dimensional evolution.展开更多
Pion generalized parton distributions are calculated within the framework of the Nambu-Jona-Lasinio model using different regularization schemes,including the proper time regularization scheme,the three-dimensional(3D...Pion generalized parton distributions are calculated within the framework of the Nambu-Jona-Lasinio model using different regularization schemes,including the proper time regularization scheme,the three-dimensional(3D)momentum cutoff scheme,the four-dimensional momentum cutoff scheme,and the Pauli-Villars regularization scheme.Furthermore,we check the theoretical constraints of pion generalized parton distributions required by the symmetries of quantum chromodynamics in different regularization schemes.The diagrams of pion parton distribution functions are plotted,in addition,we evaluate the Mellin moments of generalized parton distributions,which are related to the electromagnetic and gravitational form factors of pion.Pion generalized parton distributions are continuous but not differential at x=±ξ,when considering the effect of the contact contribution term,generalized parton distributions become not continuous at x=±ξin all the four regularization schemes.Generalized parton distributions in impact parameter space are considered,the width distribution of u quark in the pion and the meansquared<b_(⊥)^(2)>πu are calculated.The light-front transverse-spin distributions are studied when quark polarized in the light-front-transverse+x direction,the transverse-spin density is no longer symmetric around(bx=0,by=0),the peaks shift to(bx=0,by>0),we compare the average transverse shift<b_(⊥)^(y)>1u and<b_(⊥)^(y)>2u in different regularization schemes.The light-cone energy radius rE,LC and the light-cone charge radius rc,LC are also evaluated,we found that in the proper time regularization scheme the values of these quantities were the largest,in the 3 D momentum cutoff scheme they were the smallest.展开更多
We investigate a 6 D generalized Randall-Sundrum brane world scenario with a bulk cosmological constant.Each stress-energy tensor Tabi on the brane is shown to be similar to a constant vacuum energy.This is consistent...We investigate a 6 D generalized Randall-Sundrum brane world scenario with a bulk cosmological constant.Each stress-energy tensor Tabi on the brane is shown to be similar to a constant vacuum energy.This is consistent with the Randall-Sundrum model,in which each 3-brane Lagrangian yielded a constant vacuum energy.By adopting an anisotropic metric ansatz,we obtain the 5 D Friedmann-Robertson-Walker field equations.In a slightly later period,the expansion of the universe is proportional to the square root of time,t1/2,which is similar to the period of the radiation-dominated regime.Moreover,we investigate the case with two a（t） and two b（t）.In a large range of t,we obtain the 3 D effective cosmological constant Λeff=-2Ω/3>0,which is independent of the integral constant.Here,the scale factor is an exponential expansion,which is consistent with our present observation of the universe.Our results demonstrate that it is possible to construct a model that solves the dark energy problem,while guaranteeing a positive brane tension.展开更多
The kink structure in the quasiparticle spectrum of electrons in graphene observed at 200 me V below the Fermi level by angle-resolved photoemission spectroscopy（ARPES） was claimed to be caused by a tight-binding el...The kink structure in the quasiparticle spectrum of electrons in graphene observed at 200 me V below the Fermi level by angle-resolved photoemission spectroscopy（ARPES） was claimed to be caused by a tight-binding electron–phonon（e–ph） coupling in the previous theoretical studies. However, we numerically find that the e–ph coupling effect in this approach is too weak to account for the ARPES data. The former agreement between this approach and the ARPES data is due to an enlargement of the coupling constant by almost four times.展开更多
基金Supported by State Key Program of National Natural Science Foundation of China(11535005)the National Natural Science Foundation of China(11647087),the Natural Science Foundation of Yangzhou Polytechnic Institute(201917)the Natural Science Foundation of Changzhou Institute of Technology(YN1509)。
文摘To solve the cosmological constant fine tuning problem,we investigate an(n+1)-dimensional generalized Randall-Sundrum brane world scenario with two(n−1)-branes instead of two 3-branes.Adopting an anisotropic metric ansatz,we obtain the positive effective cosmological constantΩeff of order 10−124 and only require a solution≃50−80.Meanwhile,both the visible and hidden branes are stable because their tensions are positive.Therefore,the fine tuning problem can be solved quite well.Furthermore,the Hubble parameter H1(z)as a function of redshift z is in good agreement with the cosmic chronometers dataset.The evolution of the universe naturally shifts from deceleration to acceleration.This suggests that the evolution of the universe is intrinsically an extra-dimensional phenomenon.It can be regarded as a dynamic model of dark energy that is driven by the evolution of the extra dimensions on the brane.
基金Supported by the Key Program of National Natural Science Foundation of China(11535005)the National Natural Science Foundation of China(11647087)+5 种基金Foundation for Young and Yiddle-Aged Teachers Basic Ability Improvement in Guangxi Universities(2018KY0326)Special Foundation for Science and Technology Base and Talents in Guangxi(2018AD19310)China Postdoctoral Science Foundation funded project(2019M651750)Open project of state key laboratory of solid state microstructure physics(M31037)the Natural Science Foundation of Yangzhou Polytechnic Institute(201917)the Natural Science Foundation of Changzhou Institute of Technology(YN1509)。
文摘We investigate an(n+1)-dimensional generalized Randall-Sundrum model with an anisotropic metric which has three different scale factors.One obtains a positive effective cosmological constant Ωeff∼10^−124(in Planck units),which only needs a solution kr≃50−80 without fine tuning.Both the visible and hidden brane tensions are positive,which renders the two branes stable.Then,we find that the Hubble parameter is close to a constant in a large region near its minimum,thus causing the acceleration of the universe.Meanwhile,the scale of extra dimensions is smaller than the observed scale but greater than the Planck length.This may suggest that the observed present acceleration of the universe is caused by the extra-dimensional evolution.
基金Supported by the National Natural Science Foundation of China(11775118)。
文摘Pion generalized parton distributions are calculated within the framework of the Nambu-Jona-Lasinio model using different regularization schemes,including the proper time regularization scheme,the three-dimensional(3D)momentum cutoff scheme,the four-dimensional momentum cutoff scheme,and the Pauli-Villars regularization scheme.Furthermore,we check the theoretical constraints of pion generalized parton distributions required by the symmetries of quantum chromodynamics in different regularization schemes.The diagrams of pion parton distribution functions are plotted,in addition,we evaluate the Mellin moments of generalized parton distributions,which are related to the electromagnetic and gravitational form factors of pion.Pion generalized parton distributions are continuous but not differential at x=±ξ,when considering the effect of the contact contribution term,generalized parton distributions become not continuous at x=±ξin all the four regularization schemes.Generalized parton distributions in impact parameter space are considered,the width distribution of u quark in the pion and the meansquared<b_(⊥)^(2)>πu are calculated.The light-front transverse-spin distributions are studied when quark polarized in the light-front-transverse+x direction,the transverse-spin density is no longer symmetric around(bx=0,by=0),the peaks shift to(bx=0,by>0),we compare the average transverse shift<b_(⊥)^(y)>1u and<b_(⊥)^(y)>2u in different regularization schemes.The light-cone energy radius rE,LC and the light-cone charge radius rc,LC are also evaluated,we found that in the proper time regularization scheme the values of these quantities were the largest,in the 3 D momentum cutoff scheme they were the smallest.
基金Supported by the Key Program of National Natural Science Foundation of China(11535005)the National Natural Science Foundation of China(11647087 and11805097)+1 种基金the Natural Science Foundation of Yangzhou Polytechnic Institute(201917)the Natural Science Foundation of Changzhou Institute of Technology(YN1509)
文摘We investigate a 6 D generalized Randall-Sundrum brane world scenario with a bulk cosmological constant.Each stress-energy tensor Tabi on the brane is shown to be similar to a constant vacuum energy.This is consistent with the Randall-Sundrum model,in which each 3-brane Lagrangian yielded a constant vacuum energy.By adopting an anisotropic metric ansatz,we obtain the 5 D Friedmann-Robertson-Walker field equations.In a slightly later period,the expansion of the universe is proportional to the square root of time,t1/2,which is similar to the period of the radiation-dominated regime.Moreover,we investigate the case with two a（t） and two b（t）.In a large range of t,we obtain the 3 D effective cosmological constant Λeff=-2Ω/3>0,which is independent of the integral constant.Here,the scale factor is an exponential expansion,which is consistent with our present observation of the universe.Our results demonstrate that it is possible to construct a model that solves the dark energy problem,while guaranteeing a positive brane tension.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10574063,11275097,10935001,11274166,and 11075075)the National Basic Research Program of China(Grant No.2012CB921504)the Research Fund for the Doctoral Program of Higher Education,China(Grant No.2012009111002)
文摘The kink structure in the quasiparticle spectrum of electrons in graphene observed at 200 me V below the Fermi level by angle-resolved photoemission spectroscopy（ARPES） was claimed to be caused by a tight-binding electron–phonon（e–ph） coupling in the previous theoretical studies. However, we numerically find that the e–ph coupling effect in this approach is too weak to account for the ARPES data. The former agreement between this approach and the ARPES data is due to an enlargement of the coupling constant by almost four times.
