FIZIKA B 17 (2008) 3, 393  404
A NEW CLASS OF BIANCHI TYPE I VISCOUS FLUID UNIVERSE WITH A TIME DEPENDENT
COSMOLOGICAL TERM
PRADHAN^{a}, ANJU RAI^{a} and SAEED OTAROD^{b}
^{a}Department of Mathematics, Hindu Postgraduate College, Zamania232 331, Ghazipur, India
^{b}Department of Physics, Yasouj University, Yasouj, Iran
Email addresses: pradhan@iucaa.ernet.in,
acpradhan@yahoo.com,
anjuraianju@yahoo.co.in,
sotarod@mail.yu.ac.ir,
sotarod@yahoo.com
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 viscousfluid 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 (H_{1}
= A_{4}/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
