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N. D. Hari Dass

Publications and source records attributed to N. D. Hari Dass.

At least 37 records · Page 2Linked to original sources
arXiv2011

OPERA, SN1987a and energy dependence of superluminal neutrino velocity

This is a brief note discussing the energy dependence of superluminal neutrino velocities recently claimed by OPERA [1,2]. The analysis is based on the data provided there on this issue, as well as on consistency with neutrino data from SN1987a as recorded by the Kamioka detector [3]. It is seen that it is quite difficult to reconcile OPERA with SN1987a. The so called Coleman- Glashow dispersion relations do not do that well, if applied at all neutrino energies. The so called quantum gravity inspired dispersion relations perform far worse. Near OPERA energies both an energy-independent velocity, as well as a linear energy dependence with an offset that is comparable in value to the observed δv by OPERA at 28.1 GeV works very well. Our analysis shows that precision arrival time data from SN1987a still allow for superluminal behaviour for supernova neutrinos. A smooth interpolation is given that reconciles OPERA and SN1987a quite well. It suggests a fourth power energy dependence for δv of supernova neutrinos. This behaviour is insensitive to whether the velocities are energy-independent, or linearly dependent on energy, near OPERA scale of energies. Suggestions are made for experimental checks for these relations.

hep-ph↗
arXiv2011

Critique of Protective Measurements

Recently proposed idea of "protective" measurement of a quantum state is critically examined, and generalized. Earlier criticisms of the idea are discussed and their relevance to the proposal assessed. Several constraints on measuring apparatus required by "protective" measurements are discussed, with emphasis on how they may restrict their experimental feasibility. Though "protective" measurements result in an unchanged system state and a shift of the pointer proportional to the expectation value of the measured observable in the system state, the actual reading of the pointer position gives rise to several subtleties. We propose several schemes for reading pointer position, both when the apparatus is treated as a classical system as well as when its quantum aspects are taken into account, that address these issues. The tiny entanglement which is always present due to deviation from extreme adiabaticity in realistic situations is argued to be the weakest aspect of the proposal. Because of this, one can never perform a protective measurement on a single quantum system with absolute certainty. This clearly precludes an ontological status for the wave function. Several other conceptual issues are also discussed.

quant-ph↗
arXiv2010

Magnetars From Magnetized Cores Created by a Strong Interaction Phase Transition

We consider a model where the strong magnetic fields of magnetars arise from a high baryon density, magnetized core. In this framework magnetars are distinguished from pulsars by their higher masses and central density. For magnetars, as core densities exceed a threshold, the strong interaction induces a phase transition to a neutral pion condensate that aligns all magnetic moments. The core magnetic field is initially shielded by the ambient high conductivity plasma. With time the shielding currents dissipate transporting the core field out, first to the crust and then breaking through the crust to the surface of the star. Recent observations provide strong support for this model which accounts for several properties of magnetars and also enables us to identify new magnetars.

astro-ph.SR↗
arXiv2010

On string momentum in effective string theories

Centre of mass momentum for strings is an important ingredient in the calculation of the spectrum of string theories. It is calculated by the Nöther prescription for two types of conformally invariant effective string theories of the Polchinski-Strominger type. One is the so called Polyakov-Liouville theory \cite{liouville} and the other an extension of the original Polchinski-Strominger action analysed upto order $R^{-3}$ where $2πR$ is the length of the string. In the first case analysis is carried out to order $R^{-2}$ and in the second case to order $R^{-3}$. In both cases the correction to the free bosonic theory result is shown to be of the {\em improvement} type so that the correction to the total string momentum, obtained by integrating over the spatial coordinate of the string world sheet, vanishes.

hep-th↗
arXiv2010

A new form of the no-cloning theorem for harmonic oscillator coherent states

We give an alternative formulation of the no-cloning theorem that applies to harmonic oscillator coherent states. It says that {\em unknown} single harmonic oscillator coherent states can not be {\em amplified}. Conversely it says that {\em known} harmonic oscillator coherent states can be directly amplified through an universal unitary process. It is also shown that such a formulation is needed for the consistency of {\em information cloning} proposed by us long ago.

quant-ph↗
arXiv2009

Spectrum to all orders of Polchinski-Strominger {Effective} String Theory of Polyakov-Liouville Type

The spectrum of a Polchinski-Strominger type effective string theory, extended to all orders, herein called an effective string theory of the \emph{Polyakov-Liouville Type} (for obvious reasons) is investigated to all orders in the small parameter $R^{-1}$. Here $R$ is the length of the \emph{closed} string. It is established that to \emph{all orders} the spectrum of this theory is \emph{identical} to that of the free bosonic string theory. While the latter is consistent only in the critical dimension $D_c=26$, the PS- type effective string theories are by construction consistent in \emph{all} dimensions. This work extends earlier results by Drummond, and, by Hari Dass and Matlock to order $R^{-3}$. When combined with Drummond's results about absence of candidate actions at orders $R^{-4},R^{-5}$, our results imply that the spectrum of \emph{all} effective string theories coincides with that of free bosonic string theories to order $R^{-5}$. This agrees with the recent results by Aharony and Karzbrun. Our work is the first all order analysis of any effective string theory.

hep-th↗
arXiv2009

Spectrum to all orders of Polchinski-Strominger Effective String Theories of the Drummond Type

Drummond had proposed four actions for Polchinski-Strominger effective string theories at order $R^{-6}$, where $2πR$ is the length of the (closed) string >. In \cite{covariant} it had been shown, based on covariance arguments, that only two of them are independent. We analyse the spectral content of effective string theories with these two actions. We show that the inclusion of these actions does not yield corrections to the spectrum of Nambu-Goto theory \cite{Arv}.

hep-th↗
arXiv2007

Subleading properties of the QCD flux-tube in 3-d lattice gauge theory

We study the continuum limit of the string-like behaviour of flux tubes formed between static quarks and anti-quarks in three dimensional SU(2) lattice gauge theory. We compare our simulation data with the predictions of both effective string models as well as perturbation theory. On the string side we obtain clear evidence for convergence of data to predictions of Nambu-Goto theory. We comment on the scales at which the static potential starts departing from one loop perturbation theory and then again being well described by effective string theories. We also estimate the leading corrections to the one-loop perturbative potential as well as the Nambu-Goto effective string. In the intermediate regions we find an empirical formula which gives surprisingly good fits.

hep-lat↗
arXiv2007

Covariant Calculus for Effective String Theories

A covariant calculus for the construction of effective string theories is developed. Effective string theory, describing quantum string-like excitations in arbitrary dimension, has in the past been constructed using the principles of conformal field theory, but not in a systematic way. Using the freedom of choice of field definition, a particular field definition is made in a systematic way to allow an explicit construction of effective string theories with manifest exact conformal symmetry. The impossibility of a manifestly invariant description of the Polchinski-Strominger Lagrangian is demonstrated and its meaning is explained.

hep-th↗
arXiv2007

On Loop States in Loop Quantum Gravity

We explicitly construct and characterize all possible independent loop states in 3+1 dimensional loop quantum gravity by regulating it on a 3-d regular lattice in the Hamiltonian formalism. These loop states, characterized by the (dual) angular momentum quantum numbers, describe SU(2) rigid rotators on the links of the lattice. The loop states are constructed using the Schwinger bosons which are harmonic oscillators in the fundamental (spin half) representation of SU(2). Using generalized Wigner Eckart theorem, we compute the matrix elements of the volume operator in the loop basis. Some simple loop eigenstates of the volume operator are explicitly constructed.

gr-qc↗
arXiv2007

Continuum limit of string formation in 3-d SU(2) LGT

We study the continuum limit of the string-like behaviour of flux tubes formed between static quarks and anti-quarks in three dimensional SU(2) lattice gauge theory. We compare our simulation data with the predictions of both effective string models as well as perturbation theory. On the string side we obtain clear evidence for convergence of data to predictions of Nambu-Goto theory. We comment on the scales at which the static potential starts departing from one loop perturbation theory and then again being well described by effective string theories. We also estimate the leading corrections to the one-loop perturbative potential as well as the Nambu-Goto effective string. In the intermediate regions we find that a modified Lennard-Jones type potential gives surprisingly good fits.

hep-lat↗
arXiv2006

Field Definitions, Spectrum and Universality in Effective String Theories

It is shown, by explicit calculation, that the third-order terms in inverse string length in the spectrum of the effective string theories of Polchinski and Strominger are also the same as in Nambu-Goto theory, in addition to the universal Luescher terms. While the Nambu-Goto theory is inconsistent outside the critical dimension, the Polchinski-Strominger theory is by construction consistent for any space-time dimension. In the analysis of the spectrum, care is taken not to use any field redefinition, as it is felt that this has the potential to obscure important points. Nevertheless, as field redefinition is an important tool and the definition of the field should be made precise, a careful analysis of the choice of field definition leading to the terms in the action is also presented. Further, it is shown how a choice of field definition can be made in a systematic way at higher orders. To this end the transformation of measure involved is calculated, in the context of effective string theory, and thereby a quantum evaluation made of equivalence of theories related by a field redefinition. It is found that there are interesting possibilities resulting from a redefinition of fluctuation field.

hep-th↗
arXiv2006

Our response to the response hep-th/0608109 by Drummond

We have carefully examined all the points raised by Drummond in his response hep-th/0608109 to our paper hep-th/0606265 wherein we had made some criticisms of his earlier work hep-th/0411017. We concede that Drummond is correct in claiming the non-existence of R^{-4} and R^{-5} order effective string actions in the parity conserving sector, though only insofar as equivalence of field theories is considered at the classical level; the situation in unclear when quantum equivalence is taken into consideration. We still maintain the existence of such terms in the parity violating sector. Nevertheless we point out that all this has no consequence for our original proof of the nonexistence of order-R^{-3} terms. Apart from this we refute Drummond's claims about our alleged use of field redefinitions as well as his criticism of our dropping R^{-4} terms in our analysis. We reject his contention that our work is merely a partial reconstruction of his original results and that our work contains technical and conceptual errors. We do acknowledge the importance of the absence of terms pointed out by Drummond.

hep-th↗
arXiv2006

String-like behaviour of 4d SU(3) Yang-Mills flux tubes

We present here results on the fine structure of the static q\bar q potential in d=4 SU(3) Yang-Mills theory. The potential is obtained from Polyakov loop correlators having separations between 0.3 and 1.2 fermi. Measurements were carried out on lattices of spatial extents of about 4 and 5.4 fermi. The temporal extent was 5.4 fermi in both cases. The results are analyzed in terms of the force between a q\bar q pair as well as in terms of a scaled second derivative of the potential. The data is accurate enough to distinguish between different effective string models and it seems to favour the expression for ground state energy of a Nambu-Goto string.

hep-lat↗
arXiv2006

Purifications Without Entanglement, State Reconstructions and Entropy

In this paper we have analysed in detail two different purification protocols. The first one, proposed by Sudarshan, is based on the preservation of probabilities.We have constructed a second protocol here based on optimisation of fidelities. We have considered both complete and partial measurements and have established bounds and inequalities for various fidelities. For every type of measurement, we have analysed post-measurement states based on the Maximum entropy principle as well as what we have proposed as unbiased states. We show that our purification protocol always leads to better state reconstruction. These schemes can be thought of as operations in the sense of Kraus and we have explicitly constructed the Kraus operators for these. We have also shown that the entropy either increases or remains the same depending on the choice of the purification basis.

quant-ph↗
arXiv2006

Universality of correction to Luescher term in Polchinski-Strominger effective string theories

We show, by explicit calculation, that the next correction to the universal Luescher term in the effective string theories of Polchinski and Strominger is also universal. We find that to this order in inverse string-length, the ground-state energy as well as the excited-state energies are the same as those given by the Nambu-Goto string theory, the difference being that while the Nambu-Goto theory is inconsistent outside the critical dimension, the Polchinski-Strominger theory is by construction consistent for any space-time dimension. Our calculation explicitly avoids the use of any field redefinitions as they bring in many other issues that are likely to obscure the main points.

hep-th↗