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Search Results: 1 - 10 of 461413 matches for " A. Gopakumar "
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Gravitational waves from compact binaries inspiralling along post-Newtonian accurate eccentric orbits: Data analysis implications
M. Tessmer,A. Gopakumar
Physics , 2007, DOI: 10.1103/PhysRevD.78.084029
Abstract: Compact binaries inspiralling along eccentric orbits are plausible gravitational wave (GW) sources for the ground-based laser interferometers. We explore the losses in the event rates incurred when searching for GWs from compact binaries inspiralling along post-Newtonian accurate eccentric orbits with certain obvious non-optimal search templates. For the present analysis, GW signals having 2.5 post-Newtonian accurate orbital evolution are modeled following the phasing formalism, presented in [T. Damour, A. Gopakumar, and B. R. Iyer, Phys. Rev. D \textbf{70}, 064028 (2004)]. We demonstrate that the search templates that model in a gauge-invariant manner GWs from compact binaries inspiralling under qudrupolar radiation reaction along 2PN accurate circular orbits are very efficient in capturing our somewhat realistic GW signals. However, three types of search templates based on the adiabatic, complete adiabatic and gauge-dependent complete non-adiabatic approximants, detailed in [P. Ajith, B. R. Iyer, C. A. K. Robinson and B. S. Sathyaprakash, %``A new class of post-Newtonian approximants to the dynamics of inspiralling %compact binaries: Test-mass in the Schwarzschild spacetime,'' Phys. Rev. D {\bf 71}, 044029 (2005)], relevant for the circular inspiral under the qudrupolar radiation reaction were found to be inefficient in capturing the above mentioned eccentric signal. We conclude that further investigations will be required to probe the ability of various types of PN accurate circular templates, employed to analyze the LIGO/VIRGO data, to capture GWs from compact binaries having tiny orbital eccentricities.
Gravitational waves from inspiralling compact binaries: Angular momentum flux, evolution of the orbital elements and the wave form to the second post-Newtonian order
A. Gopakumar,Bala R. Iyer
Physics , 1997, DOI: 10.1103/PhysRevD.56.7708
Abstract: The post-post-Newtonian (2PN) accurate mass quadrupole moment, for compact binaries of arbitrary mass ratio, moving in general orbits is obtained by the multi-polar post Minkowskian approach of Blanchet, Damour, and Iyer (BDI). Using this, for binaries in general orbits, the 2PN contributions to the gravitational waveform, and the associated far-zone energy and angular momentum fluxes are computed. For quasi-elliptic orbits, the energy and angular momentum fluxes are averaged over an orbital period, and employed to determine the 2PN corrections to the rate of decay of the orbital elements.
Second post-Newtonian gravitational wave polarizations for compact binaries in elliptical orbits
A. Gopakumar,Bala R. Iyer
Physics , 2001, DOI: 10.1103/PhysRevD.65.084011
Abstract: The second post-Newtonian (2PN) contribution to the `plus' and `cross' gravitational wave polarizations associated with gravitational radiation from non-spinning, compact binaries moving in elliptic orbits is computed. The computation starts from our earlier results on 2PN generation, crucially employs the 2PN accurate generalized quasi-Keplerian parametrization of elliptic orbits by Damour, Sch\"afer and Wex and provides 2PN accurate expressions modulo the tail terms for gravitational wave polarizations incorporating effects of eccentricity and periastron precession.
Second post-Newtonian gravitational radiation reaction for two-body systems: Nonspinning bodies
A. Gopakumar,Bala R. Iyer,Sai Iyer
Physics , 1997, DOI: 10.1103/PhysRevD.57.6562
Abstract: Starting from the recently obtained 2PN accurate forms of the energy and angular momentum fluxes from inspiralling compact binaries, we deduce the gravitational radiation reaction to 2PN order beyond the quadrupole approximation - 4.5PN terms in the equation of motion - using the refined balance method proposed by Iyer and Will. We explore critically the features of their construction and illustrate them by contrast to other possible variants. The equations of motion are valid for general binary orbits and for a class of coordinate gauges. The limiting cases of circular orbits and radial infall are also discussed.
Padé approximants for truncated post-Newtonian neutron star models
Anshu Gupta,A. Gopakumar,Bala R. Iyer,Sai Iyer
Physics , 2000, DOI: 10.1103/PhysRevD.62.044038
Abstract: Pad\'e approximants to truncated post-Newtonian neutron star models are constructed. The Pad\'e models converge faster to the general relativistic (GR) solution than the truncated post-Newtonian ones. The evolution of initial data using the Pad\'e models approximates better the evolution of full GR initial data than the truncated Taylor models. In the absence of full GR initial data (e.g., for neutron star binaries or black hole binary systems), Pad\'e initial data could be a better option than the straightforward truncated post-Newtonian (Taylor) initial data.
Transforming water supply regimes in India: Do public-private partnerships have a role to play?
Govind Gopakumar
Water Alternatives , 2010,
Abstract: Public-private partnerships (PPP) are an important governance strategy that has recently emerged as a solution to enhance the access of marginalised residents to urban infrastructures. With the inception of neo-liberal economic reforms in India, in Indian cities too PPP has emerged as an innovative approach to expand coverage of water supply and sanitation infrastructures. However, there has been little study of the dynamics of partnership efforts in different urban contexts: What role do they play in transforming existing infrastructure regimes? Do reform strategies such as partnerships result in increased privatisation or do they make the governance of infrastructures more participative? Reviewing some of the recent literature on urban political analysis, this article develops the concept of water supply regime to describe the context of water provision in three metropolitan cities in India. To further our understanding of the role of PPP within regimes, this article sketches five cases of water supply and sanitation partnerships located within these three metropolitan cities. From these empirical studies, the article arrives at the conclusion that while PPP are always products of the regime-context they are inserted within, quite often strategic actors in the partnership use the PPP to further their interests by initiating a shift in the regime pathway. This leads us to conclude that PPPs do play a role in making water supply regimes more participative but that depends on the nature of the regime as well as the actions of partners.
New Class of Gravitational Wave Templates for Inspiralling Compact Binaries
Achamveedu Gopakumar
Physics , 2007,
Abstract: Compact binaries inspiralling along quasi-circular orbits are the most plausible gravitational wave (GW) sources for the operational, planned and proposed laser interferometers. We provide new class of restricted post-Newtonian accurate GW templates for non-spinning compact binaries inspiralling along PN accurate quasi-circular orbits. Arguments based on data analysis, theoretical and astrophysical considerations are invoked to show why these time-domain Taylor approximants should be interesting to various GW data analysis communities.
The Master Field in Generalised $QCD_2$
Rajesh Gopakumar
Physics , 1995, DOI: 10.1016/0550-3213(96)00191-5
Abstract: As an illustration of the formalism of the master field we consider generalised $QCD_2$. We show how Wilson Loop averages for an arbitrary contour can be computed explicitly and with some ease. A generalised Hopf equation is shown to govern the behaviour of the eigenvalue density of Wilson loops. The collective field description of the theory is therefore deduced. Finally, the non-trivial master gauge field and field strengths are obtained. These results do not seem easily accessible with conventional means.
${\cal N}=1$ Theories and a Geometric Master Field
Rajesh Gopakumar
Physics , 2002, DOI: 10.1088/1126-6708/2003/05/033
Abstract: We study the large $N$ limit of the class of U(N) ${\CN}=1$ SUSY gauge theories with an adjoint scalar and a superpotential $W(\P)$. In each of the vacua of the quantum theory, the expectation values $\la$Tr$\Phi^p$$\ra$ are determined by a master matrix $\Phi_0$ with eigenvalue distribution $\rho_{GT}(\l)$. $\rho_{GT}(\l)$ is quite distinct from the eigenvalue distribution $\rho_{MM}(\l)$ of the corresponding large $N$ matrix model proposed by Dijkgraaf and Vafa. Nevertheless, it has a simple form on the auxiliary Riemann surface of the matrix model. Thus the underlying geometry of the matrix model leads to a definite prescription for computing $\rho_{GT}(\l)$, knowing $\rho_{MM}(\l)$.
BPS states in Matrix Strings
Rajesh Gopakumar
Physics , 1997, DOI: 10.1016/S0550-3213(97)00586-5
Abstract: Matrix string theory (or more generally U-Duality) requires Super Yang-Mills theory to reflect a stringy degeneracy of BPS short multiplets. These are found as supersymmetric states in the Yang-Mills carrying (fractionated) momentum, or in some cases, instanton number. Their energies also agree with those expected from M(atrix) theory. A nice parallel also emerges in the relevant cases, between momentum and instanton number, (both integral as well as fractional) providing evidence for a recent conjecture relating the two.
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