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FIZIKA B 17 (2008) 3, 393 - 404
 
A NEW CLASS OF BIANCHI TYPE I VISCOUS FLUID UNIVERSE WITH A TIME DEPENDENT
COSMOLOGICAL TERM
PRADHANa, ANJU RAIa and SAEED OTARODb
aDepartment of Mathematics, Hindu Post-graduate College, Zamania-232 331, Ghazipur, India
bDepartment of Physics, Yasouj University, Yasouj, Iran
E-mail addresses: [email protected],
[email protected],
[email protected],
[email protected],
[email protected]
Received 9 April 2008; Revised manuscript received 15 September 2008
Accepted 17 September 2008 Online 17 October 2008
A new class of Bianchi type I viscous-fluid cosmological models with a
variable cosmological constant are investigated in which the expansion is
considered only in two directions, i.e. one of the Hubble parameter (H1
= A4/A) is zero. We have considered four cases: (i) coefficients of
bulk (x) and shear (h) viscosity are taken as constant, (ii) x and h are considered to be inversely dependent on time, (iii) L is taken as inverse square of t and (iv) x and h are considered as proportional to scale of expansion in the model. The
cosmological constant L is found to be positive and is a decreasing function of time which is
supported by results from recent supernovae Ia observations. Some physical and
geometric properties of the models are also discussed.
PACS numbers: 98.80.Jk, 98.80.Es
UDC 524.83
Keywords: cosmology; Bianchi type I universe, viscous fluid models, variable
cosmological constant
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