6,111 research outputs found
Topological Excitations near the Local Critical Point in the Dissipative 2D XY model
The dissipative XY model in two spatial dimensions belongs to a new
universality class of quantum critical phenomena with the remarkable property
of the decoupling of the critical fluctuations in space and time. We have shown
earlier that the quantum critical point is driven by proliferation in time of
topological configurations that we termed warps. We show here that a warp may
be regarded as a configuration of a monopoles surrounded symmetrically by
anti-monopoles so that the total charge of the configuration is zero. Therefore
the interaction with other warps is local in space. They however interact with
other warps at the same spatial point logarithmically in time. As a function of
dissipation warps unbind leading to a quantum phase transition. The critical
fluctuations are momentum independent but have power law correlations in time
Narasimham Committee Report - Some Further Ramifications and Suggestions
This paper while agreeing with the general thrust of the Narasimham Committee Report. Calls attention to some logical corollaries of the Report and analyses some possible fallout from implementing the Report. We agree with the view that control of banking system should be under an autonomous body supervised by the RBI. However at the level of individual banks, closer scrutiny of lending procedures may be called for than is envisaged in the Report. In a freely functioning capital market the potential of government bonds is enormous, but this necessitates restructuring of the government bond market. The government bonds may then also be used as suitable hedging mechanisms by introducing options and futures trading. We recommend freeing up the operation of pension and provident fund to enable at least partial investment of such funds in risky securities. In the corporate sector, we believe that the current 2:1 debt equity norm is too high and not sustainable in the long term. We envisage that high debt levels and higher interest rates, combined with higher business risk may result in greater incidence of corporate sickness. This may call for various schemes for retrenched workers and amendment to land laws for easy exit of companies. On account of interdependencies across different policies, any sequencing of their implementation may be highly problematic. We therefore suggest a near simultaneity in the implementation of various reforms in order to build up a momentum which would be irreversible if people are to have confidence that the reforms will endure, and if we are to retain our credibility with international financial institutions.
Heavy-Fermions in a Transition-Metal Compound:
The recent discovery of heavy-Fermion properties in Lithium Vanadate and the
enormous difference in its properties from the properties of Lithium Titanate
as well as of the manganite compounds raise some puzzling questions about
strongly correlated Fermions. These are disscussed as well as a solution to the
puzzles provided.Comment: late
Anomalous Resonance of the Symmetric Single-Impurity Anderson Model in the Presence of Pairing Fluctuations
We consider the symmetric single-impurity Anderson model in the presence of
pairing fluctuations. In the isotropic limit, the degrees of freedom of the
local impurity are separated into hybridizing and non-hybridizing modes. The
self-energy for the hybridizing modes can be obtained exactly, leading to two
subbands centered at . For the non-hybridizing modes, the second order
perturbation yields a singular resonance of the marginal Fermi liquid form. By
multiplicative renomalization, the self-energy is derived exactly, showing the
resonance is pinned at the Fermi level, while its strength is weakened by
renormalization.Comment: 4 pages, revtex, no figures. To be published in Physical Review
Letter
Non - Fermi Liquid Behavior in Fluctuating Gap Model: From Pole to Zero of the Green's function
We analyze non - Fermi liquid (NFL) behavior of fluctuating gap model (FGM)
of pseudogap behavior in both 1D and 2D. We discuss in detail quasiparticle
renormalization (Z - factor), demonstrating a kind of "marginal" Fermi liquid
or Luttinger liquid behavior and topological stability of the "bare" Fermi
surface (Luttinger theorem). In 2D case we discuss effective picture of Fermi
surface "destruction" both in "hot spots" model of dielectric (AFM, CDW)
pseudogap fluctuations, as well as for qualitatively different case of
superconducting d - wave fluctuations, reflecting NFL spectral density behavior
and similar to that observed in ARPES experiments on copper oxides.Comment: 11 pages, 8 figure
Ginzburg-Landau theory of superconducting surfaces under electric fields
A boundary condition for the Ginzburg-Landau wave function at surfaces biased
by a strong electric field is derived within the de Gennes approach. This
condition provides a simple theory of the field effect on the critical
temperature of superconducting layers.Comment: 4 pages, 1 figur
Swimming statistics of cargo-loaded single bacteria
Burgeoning interest in the area of bacteria-powered micro robotic systems
prompted us to study the dynamics of cargo transport by single bacteria. In
this paper, we have studied the swimming behaviour of oil-droplets attached as
a cargo to the cell bodies of single bacteria. The oil-droplet loaded bacteria
exhibit super-diffusive motion which is characterized by high degree of
directional persistence. Interestingly, bacteria could navigate even when
loaded with oil-droplets as large as 8 microns with an effective increase in
rotational drag by more than 2 orders when compared to free bacteria. Further,
the directional persistence of oil-droplet loaded bacteria was independent of
the cargo size
Hints of spin-orbit resonances in the binary black hole population
Binary black hole spin measurements from gravitational wave observations can reveal the binary's evolutionary history. In particular, the spin orientations of the component black holes within the orbital plane, and , can be used to identify binaries caught in the so-called spin-orbit resonances. In a companion paper, we demonstrate that and are best measured near the merger of the two black holes. In this work, we use these spin measurements to provide the first constraints on the full six-dimensional spin distribution of merging binary black holes. In particular, we find that there is a preference for in the population, which can be a signature of spin-orbit resonances. We also find a preference for with respect to the line of separation near merger, which has not been predicted for any astrophysical formation channel. However, the strength of these preferences depends on our prior choices, and we are unable to constrain the widths of the and distributions. Therefore, more observations are necessary to confirm the features we find. Finally, we derive constraints on the distribution of recoil kicks in the population, and use this to estimate the fraction of merger remnants retained by globular and nuclear star clusters. We make our spin and kick population constraints publicly available
Measuring binary black hole orbital-plane spin orientations
Binary black hole spins are among the key observables for gravitational wave astronomy. Among the spin parameters, their orientations within the orbital plane, , and , are critical for understanding the prevalence of the spin-orbit resonances and merger recoils in binary black holes. Unfortunately, these angles are particularly hard to measure using current detectors, LIGO and Virgo. Because the spin directions are not constant for precessing binaries, the traditional approach is to measure the spin components at some reference stage in the waveform evolution, typically the point at which the frequency of the detected signal reaches 20 Hz. However, we find that this is a poor choice for the orbital-plane spin angle measurements. Instead, we propose measuring the spins at a fixed dimensionless time or frequency near the merger. This leads to significantly improved measurements for and for several gravitational wave events. Furthermore, using numerical relativity injections, we demonstrate that will also be better measured near the merger for louder signals expected in the future. Finally, we show that numerical relativity surrogate models are key for reliably measuring the orbital-plane spin orientations, even at moderate signal-to-noise ratios like
Up-down instability of binary black holes in numerical relativity
Binary black holes with spins that are aligned with the orbital angular momentum do not precess. However, post-Newtonian calculations predict that "up-down" binaries, in which the spin of the heavier (lighter) black hole is aligned (antialigned) with the orbital angular momentum, are unstable when the spins are slightly perturbed from perfect alignment. This instability provides a possible mechanism for the formation of precessing binaries in environments where sources are preferentially formed with (anti) aligned spins. In this paper, we present the first full numerical relativity simulations capturing this instability. These simulations span orbits and - precession cycles before merger, making them some of the longest numerical relativity simulations to date. Initialized with a small perturbation of -, the instability causes a dramatic growth of the spin misalignments, which can reach near merger. We show that this leaves a strong imprint on the subdominant modes of the gravitational wave signal, which can potentially be used to distinguish up-down binaries from other sources. Finally, we show that post-Newtonian and effective-one-body approximants are able to reproduce the unstable dynamics of up-down binaries extracted from numerical relativity
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