arXiv subjects

A. Bhatnagar

Publications and source records attributed to A. Bhatnagar.

10 recordsLinked to original sources

arXiv2021

Leggett-Garg tests for macrorealism: interference experiments and the simple harmonic oscillator

Leggett-Garg (LG) tests for macrorealism were originally designed to explore quantum coherence on the macroscopic scale. Interference experiments and systems modelled by harmonic oscillators provide useful examples of situations in which macroscopicity has been approached experimentally and are readily turned into LG tests for a single dichotomic variable Q. Applying this approach to the double-slit experiment in which a non-invasive measurement at the slits is included, we exhibit LG violations. We find that these violations are always accompanied by destructive interference. The converse is not true in general and we find that there are non-trivial regimes in which there is destructive interference but the two-time LG inequalities are satisfied which implies that it is in fact often possible to assign (indirectly determined) probabilities for the interferometer paths. Similar features have been observed in recent work involving a LG analysis of a Mach-Zehnder interferometer and we compare with those results. We extend the analysis to the triple-slit experiment again finding LG violations, and we also exhibit examples of some surprising relationships between LG inequalities and NSIT conditions that do not exist for dichotomic variables. For the simple harmonic oscillator, we find an analytically tractable example showing a two-time LG violation with a gaussian initial state, echoing in simpler form recent results of Bose et al (Phys. Rev. Lett. 120, 210402 (2018)).

quant-ph↗

arXiv2020

Holography of pp-waves in conformal gravity

We consider holography of two pp-wave metrics in conformal gravity, their one point functions, and asymptotic symmetries. One of the metrics is a generalization of the standard pp-waves in Einstein gravity to conformal gravity. The holography of this metric shows that within conformal gravity one can have realised solution which has non-vanishing partially massless response (PMR) tensor even for vanishing subleading term in the Fefferman-Graham expansion (i.e. Neumann boundary conditions), and vice-versa.

hep-th↗

arXiv2002

How good are the predictions for oscillation frequencies

We have used available intermediate degree p-mode frequencies for the solar cycle 23 to check the validity of previously derived empirical relations for frequency shifts (Jain et al.: 2000, Solar Phys., 192, 487). We find that the calculated and observed frequency shifts during the rising phase of the cycle 23 are in good agreement. The observed frequency shift from minimum to maximum of this cycle as calculated from MDI frequency data sets is 251 $\pm$ 7 nHz and from GONG data is 238 $\pm$ 11 nHz. These values are in close agreement with the empirically predicted value of 271 $\pm$ 22 nHz.

astro-ph↗

arXiv2002

Variation of solar irradiance and mode frequencies during Maunder minimum

Using the sunspot numbers reported during the Maunder minimum and the empirical relations between the mode frequencies and solar activity indices, the variations in the total solar irradiance and 10.7 cm radio flux for the period 1645 to 1715 is estimated. We find that the total solar irradiance and radio flux during the Maunder minimum decreased by 0.19% and 52% respectively, as compared to the values for solar cycle 22.

astro-ph↗

arXiv2001

Temporal evolution of f-mode frequencies and radius

We have analysed temporal evolution in centroid frequencies and splitting coefficients of solar f-modes obtained from MDI/SOHO. The data were divided into 20 sets covering a period from May 1, 1996 to August 31, 2000. The variation in frequencies is estimated to be 68 nHz over the period of four years which includes the rapidly rising phase of the solar cycle 23. This change is much smaller than that observed for p-mode frequencies. It is also noticed that the f-mode frequencies appear to be weakly correlated with solar activity indices as compared to the p-mode frequencies. We have also inferred the relative change in the solar radii and notice a 1 year periodicity which may be associated with the solar cycle variation.

astro-ph↗

arXiv2001

On the solar rotation rate in the upper convection zone

We present results on variation in rotation rate in the upper convection zone using data from GONG and MDI/SOHO covering a period of more than four years. We find that the first few odd-order splitting coefficients vary systematically with the solar cycle. The rotation rate near the solar surface calculated from analytical methods agrees well with that of inversion techniques. The residual rotation rate in the outer layers seem to be correlated with the solar activity.

astro-ph↗

arXiv2001

Analysis of hysteresis effect in p mode frequency shifts and solar activity indices

Using intermediate degree p mode frequency data sets for solar cycle 22, we find that the frequency shifts and magnetic indices show a `hysteresis' phenomenon. It is observed that the magnetic indices follow different paths for the ascending and descending phases of the solar cycle, the descending path always seems to follow a higher track than the ascending one. However, for the radiative indices, the paths cross each other indicating phase reversal.

astro-ph↗

arXiv2000

Solar cycle induced variations in GONG p-mode frequencies and splittings

We have analysed the recently available GONG p-mode frequencies and splitting coefficients for a period of three and half years, including the rapidly rising phase of solar cycle 23. The analysis of mean frequency shift with different activity indices shows that the shift is equally correlated with both magnetic and radiative indices. During the onset of the new cycle 23, we notice that the change in $b_4$ splitting coefficient is more prominent than the change in $b_2$. We have estimated the solar rotation rate with varying depth and latitude. In the equatorial region, the rotation first increases with depth and then decreases, while an opposite behaviour is seen in the polar region. We also find a small but significant temporal variation in the rotation rate at high latitudes.

astro-ph↗

arXiv1999

Empirical estimate of p-mode frequency shift for solar cycle 23

We have obtained empirical relations between the p-mode frequency shift and the change in solar activity indices. The empirical relations are determined on the basis of frequencies obtained from BBSO and GONG stations during solar cycle 22. These relations are applied to estimate the change in mean frequency for the cycle 21 and 23. A remarkable agreement between the calculated and observed frequency shifts for the ascending phase of cycle 23 indicates that the derived relations are independent of epoch and do not change significantly from cycle to cycle. We propose that these relations could be used to estimate the shift in p-mode frequencies for past, present and future solar activity cycles, if the solar activity index is known. The maximum frequency shift for cycle 23 is estimated to be 265 \pm 90 nHz corresponding to the predicted maximum smoothed sunspot number 118.1 \pm 35.

astro-ph↗

arXiv1999

GONG p-mode frequency changes with solar activity

We present a correlation analysis of GONG p-mode frequencies with nine solar activity indices for the period 1995 August to 1997 August. This study includes spherical harmonic degree in the range 2 to 150 and the frequency range of 1500-3500 μHz. Using three statistical tests, the measured mean frequency shifts show strong to good correlation with activity indices. A decrease of 0.06 μHz in frequency, during the descending phase of solar cycle 22 and an increase of 0.04 μHz in the ascending phase of solar cycle 23 is observed. These results provide the first evidence for change in p-mode frequencies around the declining phase of solar cycle 22 and beginning of new cycle 23. This analysis further confirms that the temporal behaviour of the solar frequency shifts closely follow the phase of the solar activity cycle.

astro-ph↗