In this work we study gravitational lensing of the wormhole in the Eddington-inspired Born–Infeld(EiBI)spacetime that incorporates with a cosmic string.It is found that the presence of a cosmic string can enhance the...In this work we study gravitational lensing of the wormhole in the Eddington-inspired Born–Infeld(EiBI)spacetime that incorporates with a cosmic string.It is found that the presence of a cosmic string can enhance the light deflection in the strong-field limit,compared to the Ellis–Bronnikov wormhole.The magnification effects of this composite structure could cause some substantial impacts on the angle separation between the first and the rest of the images,and their relative brightness.Furthermore,based on these observables,we model some observable aspects in the strong-and the weak-field limits.The presence of a cosmic string can affect some distinguishable observables compared to the wormhole without cosmic string.This work could deepen our understanding of the spacetime structure of the wormhole in EiBI spacetime with one-dimensional topological defects.展开更多
We study a two-dimensional generalized Kemmer oscillator in the cosmic string spacetime with the magnetic field to better understand the contribution from gravitational field caused by topology defects,and present the...We study a two-dimensional generalized Kemmer oscillator in the cosmic string spacetime with the magnetic field to better understand the contribution from gravitational field caused by topology defects,and present the exact solutions to the generalized Kemmer equation in the cosmic string with the Morse potential and Coulomb-liked potential through using the Nikiforov-Uvarov(NU)method and biconfluent Heun equation method,respectively.Our results give the topological defect’s correction for the wave function,energy spectrum and motion equation,and show that the energy levels of the generalized Kemmer oscillator rely on the angular deficitαconnected with the linear mass density m of the cosmic string and characterized the metric’s structure in the cosmic string spacetime.展开更多
The recently discovered alignment of quasar polarizations on very large scales could possibly be explained by considering cosmic strings on a warped five dimensional spacetime. Compact objects, such as cosmic strings,...The recently discovered alignment of quasar polarizations on very large scales could possibly be explained by considering cosmic strings on a warped five dimensional spacetime. Compact objects, such as cosmic strings, could have tremendous mass in the bulk, while their warped manifestations in the brane can be consistent with general relativity in 4D. The self-gravitating cosmic string induces gravitational wavelike disturbances which could have effects felt on the brane, i.e., the massive effective 4D modes (Kaluza-Klein modes) of the perturbative 5D graviton. This effect is amplified by the time dependent part of the warp factor. Due to this warp factor, disturbances don’t fade away during the expansion of the universe. From a nonlinear perturbation analysis it is found that the effective Einstein 4D equations on an axially symmetric spacetime, contain a “back-reaction” term on the righthand side caused by the projected 5D Weyl tensor and can act as a dark energy term. The propagation equations to first order for the metric components and scalar-gauge fields contain -dependent terms, so the approximate wave solutions are no longer axially symmetric. The disturbances, amplified by the warp factor, can possess extremal values for fixed polar angles. This could explain the two preferred polarization vectors mod .展开更多
In this paper we investigate the scattering of massless Dirac wave from several different black hole spacetimes(i.e. the Schwarzschild black hole, the RN extremal black hole, the Schwarzschild de Sitter black hole, an...In this paper we investigate the scattering of massless Dirac wave from several different black hole spacetimes(i.e. the Schwarzschild black hole, the RN extremal black hole, the Schwarzschild de Sitter black hole, and the extremal Schwarzschild de Sitter black hole) which are influenced by the cosmic string, respectively. All these cases show us that the total absorption cross sections oscillate around the geometric-optical limit and decrease with linear mass density μof the cosmic string. All of the total scattering cross sections exhibit that the main scattering angle becomes narrower for the high partial frequency wave. Due to the influence of cosmic string, the glory peak becomes wider for larger values of linear mass density μ of the cosmic string.展开更多
We find an azimuthal-angle dependent approximate wave like solution to second order on a warped five-dimensional manifold with a self-gravitating U(1) scalar gauge field (cosmic string) on the brane using the multiple...We find an azimuthal-angle dependent approximate wave like solution to second order on a warped five-dimensional manifold with a self-gravitating U(1) scalar gauge field (cosmic string) on the brane using the multiple-scale method. The spectrum of the several orders of approximation show maxima of the energy distribution dependent on the azimuthal-angle and the winding numbers n of the subsequent orders of scalar field. This breakup of the quantized flux quanta does not lead to instability of the asymptotic wavelike solution, due to the suppression of the n-dependency in the energy mo-mentum tensor components by the warp factor. This effect is triggered by the contribution of the five dimensional Weyl tensor on the brane. This con-tribution can be understood as dark energy and can trigger the self-acceleration of the universe without the need of a cosmological constant. There is a striking relation between the symmetry breaking of the Higgs field described by the winding number and the SO(2) breaking of the axially symmetric configuration into a discrete subgroup of rotations about 180°. The discrete sequence of non-axially symmetric deviations, cancelled by the emission of gravitational waves in order to restore the SO(2) symmetry, triggers the pressure Tzz for discrete values of the azimuthal-angle. There can be a possible relation between the recently discovered angle-preferences of polarization axes of quasars on large scales and our theoretical predicted angle-dependency and can be an evidence for the existence of cosmic strings. The discovery of the increase of polarization rate in smaller subgroups of the several large-quasar groups (LQGs), the red shift dependency and the relative orientation of the spin axes with respect to the major axes of their host LQGs, point at a fractional azimuthal structure, were also found in our cosmic string model. This peculiar discontinuous large scale structure, i.e., polarizations directions of multiples of, for example, π/2 orπ/4, can be explained by the spectrum of azimuthal-angle dependent wavelike modes without the need of conventional density perturbations in standard 4D cosmological models. Carefully com-parison of the spectrum of extremal values of the first and second order φ-dependency and the distribution of the alignment of the quasar polarizations is necessary. This can be accomplished when more observational data become available.展开更多
We investigate the influence of an early matter-dominated era in cosmic history on the dynamics of cosmic strings and the resulting stochastic gravitational waves.Specifically,we examine the case where this era origin...We investigate the influence of an early matter-dominated era in cosmic history on the dynamics of cosmic strings and the resulting stochastic gravitational waves.Specifically,we examine the case where this era originates from the dark matter dilution mechanism within the framework of the minimal left-right symmetric model.By numerically solving the Boltzmann equations governing the energy densities of the relevant components,we meticulously analyze the modifications to the cosmological scale factor,the number density of cosmic string loops,and the gravitational wave spectrum.Our results reveal that the early matter-dominated era causes a characteristic suppression in the high-frequency regime of the gravitational wave spectrum,providing distinct and testable signatures for future ground-based interferometer experiments.展开更多
Recently,pulsar timing array(PTA)experiments have provided compelling evidence for the existence of the nanohertz stochastic gravitational wave background(SGWB).In this work,we demonstrated that cosmic string loops ge...Recently,pulsar timing array(PTA)experiments have provided compelling evidence for the existence of the nanohertz stochastic gravitational wave background(SGWB).In this work,we demonstrated that cosmic string loops generated from cosmic global strings offer a viable explanation for the observed nanohertz SGWB data,requiring a cosmic string tension parameter of log(Gμ)~-12 and a loop number density of log N~4.Additionally,we revisited the impact of cosmic string loops on the abundance of massive galaxies at high redshifts.However,our analysis revealed challenges in identifying a consistent parameter space that can concurrently explain both the SGWB data and observations from the James Webb Space Telescope.This indicates the necessity for either extending the existing model employed in this research or acknowledging distinct physical origins for these two phenomena.展开更多
We study stochastic gravitational waves from cosmic strings generated in an ultraviolet-complete model for pseudo-Nambu-Goldstone dark matter with a hidden U(1)gauge symmetry.The dark matter candidate in this model ca...We study stochastic gravitational waves from cosmic strings generated in an ultraviolet-complete model for pseudo-Nambu-Goldstone dark matter with a hidden U(1)gauge symmetry.The dark matter candidate in this model can naturally evade direct detection bounds and easily satisfy other phenomenological constraints.The bound on the dark matter lifetime implies an ultraviolet scale higher than 10^(9)GeV.The spontaneous U(1)symmetry breaking at such a high scale would induce cosmic strings with high tension,resulting in a stochastic gravitational wave background with a high energy density.We investigate the constraints from current gravitational wave experiments as well as the future sensitivity.We find that most viable parameter points can be well studied in future gravitational waveexperiments.展开更多
We study the possibility of probing high scale phase transitions that are inaccessible by LIGO.Our study shows that the stochastic gravitational-wave radiation from cosmic strings that are formed after the first-order...We study the possibility of probing high scale phase transitions that are inaccessible by LIGO.Our study shows that the stochastic gravitational-wave radiation from cosmic strings that are formed after the first-order phase transition can be detected by space-based interferometers when the phase transition temperature is T_(n)~O(10^(8−11))GeV.展开更多
The lensing effect of a cosmic string is studied, and some new methods are proposed to detect the cosmic string. The technique for using jets as extended gravitational lensing probes was first explored by Kronberg. We...The lensing effect of a cosmic string is studied, and some new methods are proposed to detect the cosmic string. The technique for using jets as extended gravitational lensing probes was first explored by Kronberg. We use the ＂alignment-breaking parameter＂ nc as a sensitive indicator of gravitational distortion by a wiggly cosmic string. Then, we applied the non-constant deflection angle to jets, and na of a specific jet is just related to the projected slope of the jet. At least three jets in the sample of Square Kilometer Array （SKA） would have significant signals （na 〉 10°） if the wiggly infinite cosmic string existed. The distortion of elliptical object is also studied and used to do a statistical research on the directions of axes and ellipticities of galaxies. In the direction of the string, we find that galaxies appear to be more elliptical for an observer and the distribution of apparent ellipticity changes correspondingly. The ellipticity distribution of current SDSS spiral sample has the signal- to-noise ratio up to 8.48 which is large enough for astronomical observations. The future survey, such as Large Synoptic Survey Telescope （LSST） and Dark Energy Survey （DES） would weaken the requirement of special geometry in the data processing. As a result, all kinds of distributions, including ellipticity axis distribution, would serve as probes to detect wiggly strings in the near future. In brief, if a wiggly cosmic string existed, these signals would be convenient to be observed with the future weak lensing survey or other surveys in the deep space. If there was no lensing signal in these distributions, it would give the upper limit of the abundance of infinite strings.展开更多
It is well known that thermodynamics of the black hole whose space-time isasymptotically flat obeys the four laws proposed by Bardeen, Carter and Hawking.But for the Schwarzschild type black hole whose space-time is n...It is well known that thermodynamics of the black hole whose space-time isasymptotically flat obeys the four laws proposed by Bardeen, Carter and Hawking.But for the Schwarzschild type black hole whose space-time is no longerasymptotically flat, whether the Bardeen-Carter-Hawking laws are valid is worthstudying. We all know that certain gauge theories allow possibility of topological de-展开更多
Theories on the nucleosynthesis in the very early universe show that the baryonic matter is just a fraction of the cosmic matter. Moreover, the flatness of the space geometry of the universe shows that the cosmic dens...Theories on the nucleosynthesis in the very early universe show that the baryonic matter is just a fraction of the cosmic matter. Moreover, the flatness of the space geometry of the universe shows that the cosmic density factor Ω= 1, this means that most of the cosmic matter exists in the form of dark matter. Confirmed by experiments up to the present, neutrino展开更多
The reionization and the large-scale structure formation of the universe are consi-dered as results of the secondary effects of cosmic string. Primordial supermassive (～10~6M_⊙) stars and star groups M(～10^(10)M_⊙...The reionization and the large-scale structure formation of the universe are consi-dered as results of the secondary effects of cosmic string. Primordial supermassive (～10~6M_⊙) stars and star groups M(～10^(10)M_⊙) can be formed immediately after recombinationowning to the accretions of single-string loops. The ultraviolet radiation of the starscan reionize the interstellar medium around them. The explosions of the supermassivestars sweep the interstellar medium to the shock-wave front to form mass shells of largemass and high density; the fragmentations of the mass shells lead to formations of newstars and new explosions. It is shown, when Grand Unification Theory (GUT) stringsare taken to be the seeds, the observed high ionization and large-scale cellular structureof galaxy distribution in the universe can be realized. For the usually chosen parameters,this scenario seems reasonable and imperative.展开更多
The present study deals with a spatially homogeneous and anisotropic Bianehi-I cosmological models representing massive strings with magnetic field and decaying vacuum energy density A. The energy-momentum tensor, as ...The present study deals with a spatially homogeneous and anisotropic Bianehi-I cosmological models representing massive strings with magnetic field and decaying vacuum energy density A. The energy-momentum tensor, as formulated by Letelier （1983）, has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is proportional to one of the components of shear tensor. The Einstein＇s field equations have been solved by applying a variation law for generalized Hubble＇s parameter in Bianchi-I space-time. The variation law for Hubble＇s parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential form. Using these two forms, Einstein＇s field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. We have made a comparative study of accelerating and decelerating models in the presence of string scenario. The study reveals that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. The strings eventually disappear from the universe for sufficiently large times, which is in agreement with current astronomical observations. The cosmological constant A is found to be a positive decreasing function of time which is corroborated by results from recent supernovae Ia observations. The physical and geometric properties of the models have been also discussed in detail.展开更多
We have constructed cosmological models for string cloud and domain walls coupled with quark matter in Lyra geometry. For this purpose we have solved the field equations using anisotropy feature of the universe, speci...We have constructed cosmological models for string cloud and domain walls coupled with quark matter in Lyra geometry. For this purpose we have solved the field equations using anisotropy feature of the universe, special law of variation for Hubble’s parameter proposed by Berman [78] which yields constant deceleration parameter;and time varying displacement field . Further some properties of the obtained solutions are discussed.展开更多
Considering five dimensional plane symmetric metric, we discuss a model universe with different situations, by solving the modified Einstein field equations within the framework of Lyra geometry. We obtain many intere...Considering five dimensional plane symmetric metric, we discuss a model universe with different situations, by solving the modified Einstein field equations within the framework of Lyra geometry. We obtain many interesting realistic solutions governing the present day model of the universe. Physical and kinematical properties of the models are discussed in detail.展开更多
We utilize homology and co-homology of a K3-Kähler manifold as a model for spacetime to derive the cosmic energy density of our universe and subdivide it into its three fundamental constituents, namely: 1) or...We utilize homology and co-homology of a K3-Kähler manifold as a model for spacetime to derive the cosmic energy density of our universe and subdivide it into its three fundamental constituents, namely: 1) ordinary energy;2) pure dark energy and 3) dark matter. In addition, the fundamental coupling of dark matter to pure dark energy is analyzed in detail for the first time. Finally, the so-obtained results are shown to be in astounding agreement with all previous theoretical analysis as well as with actual accurate cosmic measurements.展开更多
基金supported by the Youth Program of the Natural Science Foundation of Guangxi(Grant No.2021GXNSFBA075049)the Doctor Start-up Foundation of Guangxi University of Science and Technology(Grant No.19Z21)+3 种基金supported by the National Natural Science Foundation of China(Grant No.12165009)supported by the National Natural Science Foundation of China(Grant No.11865005)Hunan Natural Provincial Science Foundation(Grant No.2023JJ30487)supported by the starting Foundation of Guangxi University of Science and Technology(Grant No.24Z17)。
文摘In this work we study gravitational lensing of the wormhole in the Eddington-inspired Born–Infeld(EiBI)spacetime that incorporates with a cosmic string.It is found that the presence of a cosmic string can enhance the light deflection in the strong-field limit,compared to the Ellis–Bronnikov wormhole.The magnification effects of this composite structure could cause some substantial impacts on the angle separation between the first and the rest of the images,and their relative brightness.Furthermore,based on these observables,we model some observable aspects in the strong-and the weak-field limits.The presence of a cosmic string can affect some distinguishable observables compared to the wormhole without cosmic string.This work could deepen our understanding of the spacetime structure of the wormhole in EiBI spacetime with one-dimensional topological defects.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11465006 and 11565009)。
文摘We study a two-dimensional generalized Kemmer oscillator in the cosmic string spacetime with the magnetic field to better understand the contribution from gravitational field caused by topology defects,and present the exact solutions to the generalized Kemmer equation in the cosmic string with the Morse potential and Coulomb-liked potential through using the Nikiforov-Uvarov(NU)method and biconfluent Heun equation method,respectively.Our results give the topological defect’s correction for the wave function,energy spectrum and motion equation,and show that the energy levels of the generalized Kemmer oscillator rely on the angular deficitαconnected with the linear mass density m of the cosmic string and characterized the metric’s structure in the cosmic string spacetime.
文摘The recently discovered alignment of quasar polarizations on very large scales could possibly be explained by considering cosmic strings on a warped five dimensional spacetime. Compact objects, such as cosmic strings, could have tremendous mass in the bulk, while their warped manifestations in the brane can be consistent with general relativity in 4D. The self-gravitating cosmic string induces gravitational wavelike disturbances which could have effects felt on the brane, i.e., the massive effective 4D modes (Kaluza-Klein modes) of the perturbative 5D graviton. This effect is amplified by the time dependent part of the warp factor. Due to this warp factor, disturbances don’t fade away during the expansion of the universe. From a nonlinear perturbation analysis it is found that the effective Einstein 4D equations on an axially symmetric spacetime, contain a “back-reaction” term on the righthand side caused by the projected 5D Weyl tensor and can act as a dark energy term. The propagation equations to first order for the metric components and scalar-gauge fields contain -dependent terms, so the approximate wave solutions are no longer axially symmetric. The disturbances, amplified by the warp factor, can possess extremal values for fixed polar angles. This could explain the two preferred polarization vectors mod .
基金Supported by the National Natural Science Foundation of China under Grant No.10873004the State Key Development Program for Basic Research Program of China under Grant No.2010CB832803
文摘In this paper we investigate the scattering of massless Dirac wave from several different black hole spacetimes(i.e. the Schwarzschild black hole, the RN extremal black hole, the Schwarzschild de Sitter black hole, and the extremal Schwarzschild de Sitter black hole) which are influenced by the cosmic string, respectively. All these cases show us that the total absorption cross sections oscillate around the geometric-optical limit and decrease with linear mass density μof the cosmic string. All of the total scattering cross sections exhibit that the main scattering angle becomes narrower for the high partial frequency wave. Due to the influence of cosmic string, the glory peak becomes wider for larger values of linear mass density μ of the cosmic string.
文摘We find an azimuthal-angle dependent approximate wave like solution to second order on a warped five-dimensional manifold with a self-gravitating U(1) scalar gauge field (cosmic string) on the brane using the multiple-scale method. The spectrum of the several orders of approximation show maxima of the energy distribution dependent on the azimuthal-angle and the winding numbers n of the subsequent orders of scalar field. This breakup of the quantized flux quanta does not lead to instability of the asymptotic wavelike solution, due to the suppression of the n-dependency in the energy mo-mentum tensor components by the warp factor. This effect is triggered by the contribution of the five dimensional Weyl tensor on the brane. This con-tribution can be understood as dark energy and can trigger the self-acceleration of the universe without the need of a cosmological constant. There is a striking relation between the symmetry breaking of the Higgs field described by the winding number and the SO(2) breaking of the axially symmetric configuration into a discrete subgroup of rotations about 180°. The discrete sequence of non-axially symmetric deviations, cancelled by the emission of gravitational waves in order to restore the SO(2) symmetry, triggers the pressure Tzz for discrete values of the azimuthal-angle. There can be a possible relation between the recently discovered angle-preferences of polarization axes of quasars on large scales and our theoretical predicted angle-dependency and can be an evidence for the existence of cosmic strings. The discovery of the increase of polarization rate in smaller subgroups of the several large-quasar groups (LQGs), the red shift dependency and the relative orientation of the spin axes with respect to the major axes of their host LQGs, point at a fractional azimuthal structure, were also found in our cosmic string model. This peculiar discontinuous large scale structure, i.e., polarizations directions of multiples of, for example, π/2 orπ/4, can be explained by the spectrum of azimuthal-angle dependent wavelike modes without the need of conventional density perturbations in standard 4D cosmological models. Carefully com-parison of the spectrum of extremal values of the first and second order φ-dependency and the distribution of the alignment of the quasar polarizations is necessary. This can be accomplished when more observational data become available.
基金Supported by the Guangzhou Science and Technology Planning Project(2024A04J4026)。
文摘We investigate the influence of an early matter-dominated era in cosmic history on the dynamics of cosmic strings and the resulting stochastic gravitational waves.Specifically,we examine the case where this era originates from the dark matter dilution mechanism within the framework of the minimal left-right symmetric model.By numerically solving the Boltzmann equations governing the energy densities of the relevant components,we meticulously analyze the modifications to the cosmological scale factor,the number density of cosmic string loops,and the gravitational wave spectrum.Our results reveal that the early matter-dominated era causes a characteristic suppression in the high-frequency regime of the gravitational wave spectrum,providing distinct and testable signatures for future ground-based interferometer experiments.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0503304)the National Natural Science Foundation of China(Grant No.11921003)+2 种基金the New Cornerstone Science Foundation through the XPLORER PRIZEthe Chinese Academy of Sciencesthe Entrepreneurship and Innovation Program of Jiangsu Province。
文摘Recently,pulsar timing array(PTA)experiments have provided compelling evidence for the existence of the nanohertz stochastic gravitational wave background(SGWB).In this work,we demonstrated that cosmic string loops generated from cosmic global strings offer a viable explanation for the observed nanohertz SGWB data,requiring a cosmic string tension parameter of log(Gμ)~-12 and a loop number density of log N~4.Additionally,we revisited the impact of cosmic string loops on the abundance of massive galaxies at high redshifts.However,our analysis revealed challenges in identifying a consistent parameter space that can concurrently explain both the SGWB data and observations from the James Webb Space Telescope.This indicates the necessity for either extending the existing model employed in this research or acknowledging distinct physical origins for these two phenomena.
基金Supported by the National Natural Science Foundation of China(11805288)。
文摘We study stochastic gravitational waves from cosmic strings generated in an ultraviolet-complete model for pseudo-Nambu-Goldstone dark matter with a hidden U(1)gauge symmetry.The dark matter candidate in this model can naturally evade direct detection bounds and easily satisfy other phenomenological constraints.The bound on the dark matter lifetime implies an ultraviolet scale higher than 10^(9)GeV.The spontaneous U(1)symmetry breaking at such a high scale would induce cosmic strings with high tension,resulting in a stochastic gravitational wave background with a high energy density.We investigate the constraints from current gravitational wave experiments as well as the future sensitivity.We find that most viable parameter points can be well studied in future gravitational waveexperiments.
基金supported in part by the National Key Research and Development Program of China(2021YFC2203004)in part by the National Natural Science Foundation of China(12075041,12047564)+1 种基金the Fundamental Research Funds for the Central Universities of China(2021CDJQY-011,2020CDJQY-Z003)Chongqing Natural Science Foundation(cstc2020jcyj-msxmX0814)。
文摘We study the possibility of probing high scale phase transitions that are inaccessible by LIGO.Our study shows that the stochastic gravitational-wave radiation from cosmic strings that are formed after the first-order phase transition can be detected by space-based interferometers when the phase transition temperature is T_(n)~O(10^(8−11))GeV.
文摘The lensing effect of a cosmic string is studied, and some new methods are proposed to detect the cosmic string. The technique for using jets as extended gravitational lensing probes was first explored by Kronberg. We use the ＂alignment-breaking parameter＂ nc as a sensitive indicator of gravitational distortion by a wiggly cosmic string. Then, we applied the non-constant deflection angle to jets, and na of a specific jet is just related to the projected slope of the jet. At least three jets in the sample of Square Kilometer Array （SKA） would have significant signals （na 〉 10°） if the wiggly infinite cosmic string existed. The distortion of elliptical object is also studied and used to do a statistical research on the directions of axes and ellipticities of galaxies. In the direction of the string, we find that galaxies appear to be more elliptical for an observer and the distribution of apparent ellipticity changes correspondingly. The ellipticity distribution of current SDSS spiral sample has the signal- to-noise ratio up to 8.48 which is large enough for astronomical observations. The future survey, such as Large Synoptic Survey Telescope （LSST） and Dark Energy Survey （DES） would weaken the requirement of special geometry in the data processing. As a result, all kinds of distributions, including ellipticity axis distribution, would serve as probes to detect wiggly strings in the near future. In brief, if a wiggly cosmic string existed, these signals would be convenient to be observed with the future weak lensing survey or other surveys in the deep space. If there was no lensing signal in these distributions, it would give the upper limit of the abundance of infinite strings.
文摘It is well known that thermodynamics of the black hole whose space-time isasymptotically flat obeys the four laws proposed by Bardeen, Carter and Hawking.But for the Schwarzschild type black hole whose space-time is no longerasymptotically flat, whether the Bardeen-Carter-Hawking laws are valid is worthstudying. We all know that certain gauge theories allow possibility of topological de-
基金Project supported by the National Natural Science Foundation of China.
文摘Theories on the nucleosynthesis in the very early universe show that the baryonic matter is just a fraction of the cosmic matter. Moreover, the flatness of the space geometry of the universe shows that the cosmic density factor Ω= 1, this means that most of the cosmic matter exists in the form of dark matter. Confirmed by experiments up to the present, neutrino
文摘The reionization and the large-scale structure formation of the universe are consi-dered as results of the secondary effects of cosmic string. Primordial supermassive (～10~6M_⊙) stars and star groups M(～10^(10)M_⊙) can be formed immediately after recombinationowning to the accretions of single-string loops. The ultraviolet radiation of the starscan reionize the interstellar medium around them. The explosions of the supermassivestars sweep the interstellar medium to the shock-wave front to form mass shells of largemass and high density; the fragmentations of the mass shells lead to formations of newstars and new explosions. It is shown, when Grand Unification Theory (GUT) stringsare taken to be the seeds, the observed high ionization and large-scale cellular structureof galaxy distribution in the universe can be realized. For the usually chosen parameters,this scenario seems reasonable and imperative.
基金Supported in part by the Council of Science and Technology,Uttar Pradesh,India
文摘The present study deals with a spatially homogeneous and anisotropic Bianehi-I cosmological models representing massive strings with magnetic field and decaying vacuum energy density A. The energy-momentum tensor, as formulated by Letelier （1983）, has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is proportional to one of the components of shear tensor. The Einstein＇s field equations have been solved by applying a variation law for generalized Hubble＇s parameter in Bianchi-I space-time. The variation law for Hubble＇s parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential form. Using these two forms, Einstein＇s field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. We have made a comparative study of accelerating and decelerating models in the presence of string scenario. The study reveals that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. The strings eventually disappear from the universe for sufficiently large times, which is in agreement with current astronomical observations. The cosmological constant A is found to be a positive decreasing function of time which is corroborated by results from recent supernovae Ia observations. The physical and geometric properties of the models have been also discussed in detail.
文摘We have constructed cosmological models for string cloud and domain walls coupled with quark matter in Lyra geometry. For this purpose we have solved the field equations using anisotropy feature of the universe, special law of variation for Hubble’s parameter proposed by Berman [78] which yields constant deceleration parameter;and time varying displacement field . Further some properties of the obtained solutions are discussed.
文摘Considering five dimensional plane symmetric metric, we discuss a model universe with different situations, by solving the modified Einstein field equations within the framework of Lyra geometry. We obtain many interesting realistic solutions governing the present day model of the universe. Physical and kinematical properties of the models are discussed in detail.
文摘We utilize homology and co-homology of a K3-Kähler manifold as a model for spacetime to derive the cosmic energy density of our universe and subdivide it into its three fundamental constituents, namely: 1) ordinary energy;2) pure dark energy and 3) dark matter. In addition, the fundamental coupling of dark matter to pure dark energy is analyzed in detail for the first time. Finally, the so-obtained results are shown to be in astounding agreement with all previous theoretical analysis as well as with actual accurate cosmic measurements.
