Nonlinear anisotropy growth in Bianchi-I spacetime in metric 
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 cosmology

Bhattacharya, Kaushik; Chakraborty, Saikat

doi:10.1103/physrevd.99.023520

Cited by 9 publications

(8 citation statements)

References 44 publications

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“…We do not set a lower limit for the spin periods. We use the standard expression B P 2 = 0.17 × 10 12 G s −2 (4) (Ruderman & Sutherlandt 1975;Bhattacharya et al 1992) for the pulsar death line. Note that the exact location of the death line is still under debate (see, e.g., Zhang et al 2000;Zhang 2002;Zhou et al 2017).…”

Section: Magnetic Field and Spin-period Evolutionmentioning

confidence: 99%

Millisecond Pulsars and Black Holes in Globular Clusters

Kremer

Chatterjee

et al. 2019

ApJ

119

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Over a hundred millisecond radio pulsars (MSPs) have been observed in globular clusters (GCs), motivating theoretical studies of the formation and evolution of these sources through stellar evolution coupled to stellar dynamics. Here we study MSPs in GCs using realistic N -body simulations with our Cluster Monte Carlo code. We show that neutron stars (NSs) formed in electron-capture supernovae (including both accretion-induced and merger-induced collapse of white dwarfs) can be spun up through mass transfer to form MSPs. Both NS formation and spin-up through accretion are greatly enhanced through dynamical interaction processes. We find that our models for average GCs at the present day with masses ≈ 2 × 10 5 M can produce up to 10 − 20 MSPs, while a very massive GC model with mass ≈ 10 6 M can produce close to 100. We show that the number of MSPs is anti-correlated with the total number of stellar-mass black holes (BHs) retained in the host cluster. The radial distributions are also affected: MSPs are more concentrated towards the center in a host cluster with a smaller number of retained BHs. As a result, the number of MSPs in a GC could be used to place constraints on its BH population. Some intrinsic properties of MSP systems in our models (such as the magnetic fields and spin periods) are in good overall agreement with observations, while others (such as the distribution of binary companion types) less so, and we discuss the possible reasons for such discrepancies. Interestingly, our models also demonstrate the possibility of dynamically forming NS-NS and NS-BH binaries in GCs, although the predicted numbers are very small.

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Section: Magnetic Field and Spin-period Evolutionmentioning

confidence: 99%

Millisecond Pulsars and Black Holes in Globular Clusters

Kremer

Chatterjee

et al. 2019

ApJ

119

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“…The dynamics of the Bianchi-I metric (12) under f (R) gravity in presence of such an isotropic fluid can be described by the following set of equations [40,41],…”

Section: Isotropic Fluidmentioning

confidence: 99%

“…where δ · β ′ is defined analogously to (26), instead of (39) and (40). Again, given some form of the function f (R), we can find the Einstein frame scalar field potential V (φ) by using Eq.…”

Section: Anisotropic Fluidmentioning

confidence: 99%

Dynamical equivalence of f(R) gravity in Jordan and Einstein frames

2019

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We investigate the dynamics of f (R) gravity in Jordan and Einstein frames. First, we perform a phase-space singularities analysis in both frames. We show that, typically, anisotropic singularities are absent in the Einstein frame, whereas they may appear in the Jordan frame. We conciliate this apparent inconsistency by showing that the necessary conditions for the existence of the Einstein frame are namely the same ones assuring the absence of the anisotropic singularities in the Jordan frame. In other words, we show that, at least in the context of Bianchi I cosmologies, the Einstein frame is available only when the original formulation in the Jordan frame is free of anisotropic singularities. Furthermore, we present a novel dynamical system formulation for anisotropic cosmologies in which both frames, provided they exist, will be manifestly equivalent from the dynamical point of view, even though they fail to be diffeomorphic in general. Our results could help not only the construction of viable (free of anisotropic singularities) f (R) cosmological models, but also contribute to the still active debate on the physical interpretation of the two frames.

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“…They also argued that this may be due to scattering from large scale inhomogeneities in the line of sight to the pulsar. Bhattacharya et al (1992) fitted a broken power-law (sum of two power-laws) to the τ sc −DM relation, since they saw a flattening from a simple power-law spectrum at low DMs (below a DM of ∼30 pc cm −3 ). Their fit showed that the measured τ sc follows Kolmogorov turbulence at low DMs and deviates at higher DMs.…”

Section: Dm Dependence Of Scatteringmentioning

confidence: 99%

“…Thus, we chose 200 MHz as a reference frequency for comparison of different models. The model relations we chose from the literature are (1) a simple power law model (Slee et al 1980;Alurkar, Slee & Bobra 1986), (2) a broken power law model as in Equation 4, (3) a broken power law model by fixing the value of ζ = 2.2 in Equation 4 (Bhattacharya et al 1992;Ramachandran et al 1997), and (4) a second order polynomial fit following Bhat et al (2004) as given in Equation 5. Since we measured α for the pulsars used in this study, we have scaled τ sc using it and removed the last term in Equation 5 while fitting (Lewandowski et al 2015a;Geyer et al 2017).…”

Section: Dm Dependence Of Scatteringmentioning

confidence: 99%

Multi-frequency Scatter-broadening Evolution of Pulsars. II. Scatter-broadening of Nearby Pulsars

Krishnakumar

Maan

Joshi

et al. 2019

ApJ

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We present multi-frequency scatter broadening evolution of 29 pulsars observed with the LOw Frequency ARray (LOFAR) and Long Wavelength Array (LWA). We conducted new observations using LOFAR Low Band Antennae (LBA) as well as utilized the archival data from LOFAR and LWA. This study has increased the total of all multi-frequency or wide-band scattering measurements up to a dispersion measure (DM) of 150 pc cm −3 by 60%. The scatter broadening timescale (τ sc ) measurements at different frequencies are often combined by scaling them to a common reference frequency of 1 GHz. Using our data, we show that the τ sc -DM variations are best fitted for reference frequencies close to 200-300 MHz, and scaling to higher or lower frequencies results in significantly more scatter in data. We suggest that this effect might indicate a frequency dependence of the scatter broadening scaling index (α). However, a selection bias due to our chosen observing frequencies can not be ruled out with the current data set. Our data did not favour any particular model of the DM -τ sc relations, and we do not see a statistically significant break at the low DM range in this relation. The turbulence spectral index (β) is found to be steeper than that is expected from a Kolmogorov spectrum. This indicates that the local ISM turbulence may have a low wave-number cutoff or presence of large scale inhomogeneities in the line of sight to some of the reported pulsars.

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Nonlinear anisotropy growth in Bianchi-I spacetime in metric f(R) cosmology

Cited by 9 publications

References 44 publications

Millisecond Pulsars and Black Holes in Globular Clusters

Millisecond Pulsars and Black Holes in Globular Clusters

Dynamical equivalence of f(R) gravity in Jordan and Einstein frames

Multi-frequency Scatter-broadening Evolution of Pulsars. II. Scatter-broadening of Nearby Pulsars

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