Open Journal of Applied Sciences, 2013, 3, 89-93 doi:10.4236/ojapps.2013.31B1018 Published Online April 2013 (http://www.scirp.org/journal/ojapps) 1-A Cosmological Model with Varying G and in General Relativity Harpreet, R. K. Tiwari, H. S. Sahota Department of Applied Sciences , Sant Baba Bhag Singh Institute of Engineering & Technology, Khiala, Padhiana, Jalandhar- 144030,Punjab, India Email: sahota.harpreet@rediffmail.com Received 2013 ABSTRACT In this paper homogeneous Bianchi type -I space-time with variable G and containing matter in the form of a perfect fluid assuming the cosmological term proportional to H2 (where H is Hubble Parameter). Initially the model has a point type singularity, gravitational constant G (t) is decreasing and cosmological constant is infinite at this time. When time increases, decrease. The model does not approach isotropy, if it is small. The model is quasi-isotropic for large value of it. Keywords: Bianchi Type-I Universe; Varying G and ; Cosmology; Hubble Parameter 1. Introduction Cosmology is study of large scale structures of universe. The simplest homogeneous and anisotropic model is Bi-anchi type –I cosmological model which is gener- aliza-tion of Friedmann-Robertson-Walker (FRW) model. Cosmological model with cosmological constant are se- rious participants to describe the dynamics of the uni- verse. The origin of universe is greatest cosmological mystery even today. As we are aware that the expansion of the universe is undergoing time acceleration Perlmut- ter et al.,(1997,1998,1999), Riess et al.,(1998,2004), Al- len et al.,(2004), Peebles et al.,(2003), Padmanabhan. (2003) & Lima.(2004).To resolve the problem of a huge differ-ence between the effective cosmological constant ob-served today and the vacuum energy density predicted by the quantum field theory, several mechanisms have been proposed by (Weinberg, 1989). A possible way is to consider a varying cosmological term due to the coupling of dynamic degree of freedom with the matter fields of the universe. The cosmological constant is small because the uni- verse is old. Models with dynamically decaying cosmo- logical term representing the energy density of vacuum have been studied by Vishwakarma, R. G. (2000, 2001,2005), Arbab, A. I.(1998), Berman, M. S.(1991a, 1991b). Cosmological scenarios with a time varying cosmological constant were proposed by several re- searchers. A number of models with different decay laws for the variation of cosmological term were investigated during the last two decades Chen & Wu (1990); Pavan (1991); Carvalho et al.,(1992); Lima & Maia(1994); Lima & Trodden (1996); Arbab & Abdel-Rahman(1994); Cunha & Santos (2004); Carneiro & Lima(2005). A number of authers investigated Bianchies models, using the approach that there is link between variation of gravitational constant and cosmological constant [Abdel- Rahman 1990;Berman 1991a ;Kalligas et al.1992; Ab- dussattar and Vishkarma 2005;Pradhan et al 2006;Singh and Tiwari 2007 ]. Lot of work has been done by Saha (2005a, 2005b, 2006a, 2006b), in studying the anisot- ropic Bianchi type-I Cosmological Model in general relativity with varying G and. In this paper we study homogeneous Bianchi type -I space-time with variable G and containing matter in the form of a perfect fluid. We obtain solution of the Einstein field equations assuming the cosmological term proportional to H2 (where H is Hubble Parameter). 1.1. The Metric and Field Equations We consider the Bianchi type - I metric in the orthogonal form (1) The non-zero components of the Ricci tensor Rij. We assume that cosmic matter is taken to be perfect fluid given by the energy- momentum tensor (2) where p, are the isotropic pressure and energy density of the fluid. We take equation of state Copyright © 2013 SciRes. OJAppS
HARPREET ET AL. 90 (2 1) vi is four velocity vector of the fluid satisfying (3) Einstein's field equations with time dependent G and are (4) For the metric (1) and energy-momentum tensor (2) in commoving system of coordinates, the field equation (4) yields. (5) (6) (7) (8) In view of vanishing of the divergence of Einstein tensor, we have (9) The usual energy conservation equation of general relativity quantities is (10) Equation (9) together with (10) puts G and in some sort of coupled field given by (11) implying that is a constant whenever G is constant. Using equation (21) in equation (10) and then integrating, we get k> 0 (111) We define, R as the average scale factor of Bianchi type- I universe. (12) The Hubble parameter H, volume expansion , shear and deceleration parameter q are given by Einstein's field equations (5)-(8) can be also written in terms of Hubble parameter H, shear and decelera- tion parameter q as (13) (14) On integrating (5) - (8), we obtain (15) and (16) Where k1 and k2 are constants of integration. From (14), we obtain (17) Implying that 0 Thus the presence of positive lowers the upper limit of anisotropy whereas a negative contributes to the anisotropy. Equation (17) can also be written as (18) where 2 3 8 c G is the critical density and 8 vG is the vacuum density. From (13) and (14), we get, (19) Copyright © 2013 SciRes. OJAppS
HARPREET ET AL. 91 Thus the universe will be in decelerating phase for negative and for positive universe will slow down the rate of decrease showing that the rate of volume ex- pansion decreases during time evolution and presence of positive , slows down the rate of this decrease whereas a negative would promote it. 1.2. Solution of the Field Equation The system of equations (5)-(8) and (11) supply only five equations in seven unknown parameters (A, B, C,, p, , and G). Two extra equations are needed to solve the sys- tem completely. For this purpose we take cosmological term is proportional to H2 . (20) This variation law was proposed by Olson, et al., (1987), Pavon(1991), Maia, et al., (1994); Silveira, et al., (1994, 1997), Torres, et al.,(1996).Because observations suggest that is very small in the present universe, a decreasing functional form permits to be large in early universe. Using equation (111) and equation (20) in equation (11) we get (21) From equations (13), (14), (20) and (201) we get (22) Find the time evolution of Hubble parameter, integrate (22), we get (23) where t0 is a constant of integration. The integration con- stant is related to the choice of origin of time. From equation (23), we obtain the scale factor (24) By using equation (24) in (15) and (16), the metric (1), we get (25) where M = and m1,m2 and m3 are constants. For the model (25), the spatial V, density , gravitational con- stant G and cosmological constant are (26) (27) (28) (29) Expansion scalar and shear are (30) (31) (32) (33) (34) (35) 2. Observations and Conclusions 1. Thus we observe that as spatial volume V0 at t = 0 and expansion scalar is infinite, which shows that universe starts evolving with zero volume at t = 0 infinite rate of expansion. Hence the model has a point type sin- gularity at initial epoch. 2. Initially at t = 0 the energy density ‘ ’, pres-sures ‘p’, shear ,cosmological term tend all infinite. 3. As t increases the spatial volume increases but the expansion rate decreases. Thus the rate of expansion slows down with increase in time and tend to zero. 4. As t the spatial volume V becomes infi-nitely large. All parameters , , p, ,Ὠ, , 0 asymptotically but G is decreasing. Therefore at large value of t model gives empty universe. The cosmic scenario starts from a big bang at t = 0 and continues until t=. 5. The ratio / 0 as t∞. So the model ap-proach isotropy for large value of t. 6. We also see for model (25), if t ∞ then q =2 im- plies universe is decelerating as q is positive. 7. The possibility of G increasing with time, at least in some stages of the development of the universe, has been investigated by Abdel-Rahman (1990), Chow (1981), Levit (1980) and Milne (1935). 2 1 T Include Copyright © 2013 SciRes. OJAppS
HARPREET ET AL. 92 Berman (1990), Ber-man and Som (1990), Berman et al. (1989), and Bertolami (1986b, 1986a). This form of is physically reasonable as observations suggest that is very small in the present universe. A decreasing func- tional form permits to be large in the early universe. 8. In summary, we observed on investigation that Bi- anchi type-I cosmological model with variable G and in presence of perfect fluid with cos-mological term is proportional to H2 (H is Hub-ble Parameter) suggested by Silveira et al., (1994,1997) and others. Initially the model has a point type singularity, gravitational constant G (t) is decreasing and cosmological constant is in- finite at this time when time increases decrease.The model approach isotropy for large value of t ,the model is quasi-isotropic i.e. 0. REFERENCES [1] A. Pradhan and P. Pandey, “Some Bianchi Type I Vis- cous Fluid Cosmological Models with a Variable Cos- mological Constant Astrophys,” 2006, Space Science, Vol. 301, p. 221. [2] B. Saha, “Anisotropic Cosmological Models with a Per- fect Fluid and a ᴧ Term,” Astrophysics and Space Science, Vol. 302, No. 1-4, 2006a, pp. 83-91. doi:10.1007/s10509-005-9008-5 [3] B. Saha, “Anisotropic Cosmological Models with a Per- fect Fluid and Dark Energy Reexamined,” International Journal of Theoretical Physics, Vol. 45, No. 5, 2006b, pp. 952-964. [4] B. Saha, “Bianchi Type I Universe with Viscous Fluid,” Modern Physics Letters A, Vol. 20, No. 28, 2005a, p. 2127. doi:10.1142/S021773230501830X [5] B. Saha, “Anisotropic Cosmological Models with Perfect Fluid and Dark Energy,” Chinese, 2005b. [6] R. G. Vishwakarma, “A Model to Explain Varying ᴧ,G and Simultaneously,” General Relativity and Gravi- tation, Vol. 37,2005, pp. 1305-1311. doi:10.1007/s10714-005-0113-0 [7] S. Carneiro and J. A. S. Lima, “Time Dependent Cosmo- logical Term and Holography,” International Journal of Modern Physics A, Vol. 20, No. 11, 2005, p. 2465. doi:10.1142/S0217751X0502478X [8] R. K. Tiwari, “An LRS Bianchi Type–I Cosmological Models with Time Dependent L Term,” International Journal of Modern Physics D, Vol. 16, No. 4, 2007, pp. 745-754. doi:10.1142/S0218271807009863 [9] J. V. Cunha and R. C. Santos, “The Existence of an Old Quasar at z=3.91 and Its Implications for λ(t) Deflation- ary Cosmologies,” International Journal of Modern Phys- ics D, Vol. 13, 2004, p. 1321. doi:10.1142/S0218271804005481 [10] A. G. Riess, et al., “Type Ia Supernova Discoveries at z > 1 from the Hubble Space Telescope: Evidence for Past Deceleration and Constraints on Dark Energy Evolu- tion*,” The Astrophysical Journal, Vol. 607, 2004, p. 665. doi:10.1086/383612 [11] S. W. Allen, et al., “Constraints on Dark Energy from Chandra Observations of the Largest Relaxed Galaxy Clusters,” Monthly Notices of the Royal Astronomical So- ciety, Vol. 353, No. 2, 2005, pp. 457-467. doi:10.1111/j.1365-2966.2004.08080.x [12] J. A. S. Lima, “Alternative Dark Energy Models: An Overview,” Brazilian Journal of Physics, Vol. 34, No. 1a, 2004, pp. 194-200. doi:10.1590/S0103-97332004000200009 [13] T. Padmanabhan, “Cosmological Constant the Weight of the Vacuum,” Physics Reports, Vol. 380, No. 5-6, 2003, pp. 235-320. doi:10.1016/S0370-1573(03)00120-0 [14] P. J. E. Peebles and B. Ratra, “The Cosmological Con- stant and Dark Energy,” Reviews of Modern Physics, Vol. 75, No. 2,2003, pp. 559-606. doi:10.1103/RevModPhys.75.559 [15] R. G. Vishwakarma, “Study of the Magnitude-Redshift Relation for Type Ia Supernovae in a Model Resulting from a Ricci-Symmetry,” General Relativity and Gravita- tion, Vol. 33, No. 11, 2001, pp. 1973-1984. doi:10.1023/A:1013051026760 [16] R. G. Vishwakarma, “A Study of Angular Size-redshift Relation for Models in Which ᴧ Decays as the Energy Density,” Class Quantum Gravity, Vol. 17, 2000, pp. 38-33. doi:10.1088/0264-9381/17/18/317 [17] S. Perlmutter, et al., “Measurements of Ω and Λ from 42 High-Redshift Supernovae,” The Astrophysical Journal, Vol. 517, No. 2, 1999, p. 565. doi:10.1086/307221 [18] I. Arbab, “Bianchi Type I Universe with Variable G and ᴧ,” General Relativity and Gravitation, Vol. 30, No. 9, 1998, pp. 1401-1405. doi:10.1023/A:1018856625508 [19] S. Perlmutter, et al., “Discovery of a Supernova Explo- sion at Half the Age of the Universe,” Nature, Vol. 391 1998, p. 51. [20] A. G. Riess, et al., “Observational Evidence from Super- novae for an Accelerating Universe and a Cosmological Constant,” The Astrophysical Journal, Vol. 116, 1998, P. 1009. [21] S. Perlmutter, et al., “Measurements of the Cosmological Parameters Ω and Λ from the First Seven Supernovae at z ≥ 0.35,” The Astrophysical Journal, Vol. 483, No. 2, 1997, p. 565. doi:10.1086/304265 [22] V. Silveira and J. Waga, “Cosmological Poperties of a Class of ᴧ Decaying Cosmologies,” Physical Revview D, Vol. 56, 1997, p. 4625. [23] J. A. S. Lima and M. Trodden, “Decaying Vacuum En- ergy and Deflationary Cosmology in Open and Closed Universes,” Physical Revview D, Vol. 53, No. 8,1996, pp. 4280-4286. doi:10.1103/PhysRevD.53.4280 [24] J. A. S. Lima, “Thermodynamics of Decaying Vacuum Cosmologies,”Physical Revview D, Vol. 54, No. 4, 1996, pp. 2571-2577. doi:10.1103/PhysRevD.54.2571 Copyright © 2013 SciRes. OJAppS
HARPREET ET AL. Copyright © 2013 SciRes. OJAppS 93 [25] L. F. B. Torres and I. Waga, “Decaying Lambda Cos- mologies and Statistical Properties of Gravitational Lens- es,” Monthly Noices of the Royal Astronomical Society, Vol. 279, No. 3,1996, pp. 712-726. doi:10.1093/mnras/279.3.712 [37] D. Pavon, “Nonequilibrium Fluctions in Cosmic Vacuum Decay,” Physical Review D, Vol. 43, No. 2,1991, pp. 375-378. doi:10.1103/PhysRevD.43.375 [38] Abdel - Rahaman, AMM (1990).A Critical Density Cos- mological Model with Varying Gravitation and Cosmo- logical”Constants”General Relativity and Gravitation Vol. 22, No. 6, p. 655.doi:10.1007/BF00755985 [26] D. Kalligas, P. S. Wesson and C. W. F. Everitt, “Bianchi type I Cosmological Models with VariableG and Λ: A Comment,” General Relativity and Gravitation, Vol. 27, No. 6, 1995, pp. 645-650. doi:10.1007/BF02108066 [39] Berman MS, Static Universe in a Modified Brans-Dicke Cosmology. International Journal of Theoretical Physics. Vol. 29, No. 6,1990, pp. 567-570. doi:10.1007/BF00672031 [27] A. I. Arbab and A. M. M. Abdel-Rahaman, “Nonsingular Cosmology with a Time-dependent Cosmological Term,” Physical Revview D, Vol. 50, No. 12,1994, pp. 7725-7728. doi:10.1103/PhysRevD.50.7725 [40] Berman MS and Som MM Brans-Dicke Models with Time-Dependent Cosmological Term, International Jour- nal of Theoretical Physics , Vol. 29, No. 12,1990, pp. 1411-1414. doi:10.1007/BF00674120 [28] A. Beesham, “Bianchi Type I Cosmological Models with VariableG and A,” General Relativity and Gravitation , Vol. 26, No. 2,1994, pp. 159-165. doi:10.1007/BF02105151 [41] W. Chen and Y. S. Wu, “Implication of a Cosmological Constant Varying as ,” Physical Review D, Vol. 41,1990, p. 695. [29] J. A. S. Lima and J. M. F. Maia, “Deflationary Cosmol- ogy with Decaying Vacuum Energy Density,” Physical Revview D, Vol. 49, No. 10,1994, pp. 5597-5600. doi:10.1103/PhysRevD.49.5597 [42] E. A. Milne, “Relativity, Gravitation and World Struc- ture,” Oxford University Press, Oxford ,1935. [43] M. S. Berman, M. M. Som and F. M. Gomide, “Brans-Dicke Static Universes,” General Relativity and Gravitation, Vol. 21, No. 3,1989, pp. 287-292. doi:10.1007/BF00764101 [30] J. A. S. Lima and J. C. Carvalho, “Dirac's Cosmology with Varying Cosmological Constant,” General Relativity and Gravitation, Vol. 26, No. 9, pp. 909-916. doi:10.1007/BF02107147 [44] S. Weinberg, “The Cosmological Constant Problem,” Reviews of Modern Physics, Vol. 61, No. 1,1989, pp. 1-23. doi:10.1103/RevModPhys.61.1 [31] M. D. Maia and G. S. Silva, “Geometrical Constraints on the Cosmological Constant,” Physical Review D, Vol. 50, No. 12 ,1994, pp. 7233-7238. doi:10.1103/PhysRevD.50.7233 [45] T. S. Olson and T. F. Jordan, “Ages of the Universe for Decreasing Cosmological Constants,” Physical Review D, Vol. 35, 1987, p. 3258.doi:10.1103/PhysRevD.35.3258 [32] V. Silveira and J. Waga, “Decaying ᴧ Cosmologies and Power Spectrum,” Physical Review D. Vol. 50, No. 8,1994, 4890-4894. doi:10.1103/PhysRevD.50.4890 [46] O. Bertolami, “Brans-Dicke Cosmology with a Scalar Field Dependent Cosmological Term,” Fortsch Physic- sics, Vol. 34,1986b, p. 829. [33] J. C. Carvalho, J. A. S. Lima and I. Waga, “Cosmological Consequences of a Time-Dependent Term,” Physical Review D, Vol. 46, No. 6,1992, pp. 2404-2407. doi:10.1103/PhysRevD.46.2404 [47] O. Bertolami, “Time-Dependence Cosmological Term,” Nuovo Cimento B, Vol. 93, No. 1,1986a, pp. 36-42. doi:10.1007/BF02728301 [48] T. L. Chow, “The Variability of the Gravitational Con- stant,” Nuovo Cimento Lettere, Vol. 31, No. 4, 1981, pp. 119-120. doi:10.1007/BF02822409 [34] D. P. S. Kalligas, Wesson and C. W. F. Everitt, “Flat FRW Models with VariableG and Λ,” General Relativity and Gravitation, Vol. 24, No. 4, 1992, pp. 351-357. doi:10.1007/BF00760411 [49] L. S. Levitt, “The Gravitational Constraint at Time Zero,” Nuovo Cimento,Lettere, Vol. 2, No. 29,1980, p. 23. [35] M. S. Berman, “Cosmological Models with Variable Gravitational and Cosmological ‘Constants’,” General Relativity and Gravitation, Vol. 23, No. 4,1991a, pp. 465-469. doi:10.1007/BF00756609 [50] V. Silveira and J. Waga, “Decaying ᴧ Cosmologies and Power Spectrum,” Physical Review D, Vol. 50, No. 8, 1994, pp. 4890-4894. doi:10.1103/PhysRevD.50.4890 [36] M. S. Berman, “Cosmological Models with Variable Cosmological Term,” Physical Review D, 1991b, pp. 1075-1078. [51] V. Silveira and J. Waga, “Cosmological Properties of a Class of ᴧ Decaying Cosmologies,” Physical Revview D, Vol. 56, 1997, p. 4625.
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