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Nuclear Theory·nucl-th

Tuesday·June 13, 2023

12 papers—9 primary·3 cross-listed

All12Primary9Cross-lists3
  1. 10

    [Submitted on 26 May 2023] (cross-list from astro-ph.HE)

    Pulsar as a Weber detector of gravitational waves and a probe to its internal phase transitions

    Partha Bagchi🇮🇳 · Oindrila Ganguly🇮🇳 · Biswanath Layek🇮🇳 · Anjishnu Sarkar🇮🇳 · Ajit M. Srivastava🇮🇳

    It is believed that cores of neutron stars provide a natural laboratory where exotic high baryon density QCD phases may exist.The theoretically well established {\it neutron superfluid phase} is also believed to be found only inside neutron stars. Focus on neutron stars has intensified in recent years with the direct detection of gravitational waves (GWs) from binary neutron star (BNS) merger, which has allowed the possibility of directly probing the properties of the interior of a neutron star. A remarkable phenomenon manifested by rapidly rotating neutron stars is in their {\it avatar} as {\it Pulsars}. The accuracy of pulsar timing allowed the first indirect detection of GWs from a BNS system and opened up a few exciting possibilities. Any pulsar deformation, even if incredibly tiny, can leave imprints on the pulses by introducing tiny perturbations of the moment of inertia (MI) tensor components. While the diagonal MI components of the perturbed MI tensor affect the pulse timings, the off-diagonal components lead to the pulsar's wobbling and affecting the pulse profile. This opens up an opportunity to explore various phase transitions inside a pulsar core by induced density fluctuations through the observable effects on the pulse timing and profile. Such perturbations also naturally induce a rapidly changing quadrupole moment of the star, thereby providing a new source of GW emission. Another remarkable possibility arises when we consider the effect of an external GW on a neutron star. With the possibility of detecting any minute changes in its configuration through pulse observations, the neutron star has the potential to perform as a Weber detector of GWs. This brief review focuses on these specific aspects of a pulsar, specifically on the type of physics that can be probed by utilizing the effect of changes in the MI tensor on pulse properties.

    Comments:
    Review article (revised), 31 pages, title changed, abstract reduced, fig.6 is corrected (larger fonts), references added, accepted for publication in Modern Physics Letters A (MPLA)
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2305.16850 [pdf]
    Mod.Phys.Lett.A(2024)·5 citations
  2. 11

    [Submitted on 9 Jun 2023] (cross-list from physics.comp-ph)

    On the unimportance of memory for the time non-local components of the Kadanoff-Baym equations

    Cian C. Reeves · Yuanran Zhu · Chao Yang · Vojtech Vlcek

    The generalized Kadanoff-Baym ansatz (GKBA) is an approximation to the Kadanoff-Baym equations (KBE), that neglects certain memory effects that contribute to the Green's function at non-equal times. Here we present arguments and numerical results to demonstrate the practical insignificance of the quantities neglected when deriving the GKBA at conditions at which KBE and GKBA are appropriate. We provide a mathematical proof that places a scaling bound on the neglected terms, further reinforcing that these terms are typically small in comparison to terms that are kept in the GKBA. We perform calculations in a range of models, including different system sizes and filling fractions, as well as experimentally relevant non-equilibrium excitations. We find that both the GKBA and KBE capture the dynamics of interacting systems with moderate and even strong interactions well. We explicitly compute terms neglected in the GKBA approximation and show, in the scenarios tested here, that they are orders of magnitude smaller than the terms that are accounted for, i.e., they offer only a small correction when included in the full Kadanoff-Baym equations.

    Comments:
    14 pages, 3 figures, Supplemental information with 10 figures
    Subjects:
    Computational Physics (physics.comp-ph); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
    arXiv:
    2306.06225 [pdf]
    PRB(2023)·4 citations
  3. 12

    [Submitted on 12 Jun 2023] (cross-list from hep-lat)

    Dynamics of the critical point in QCD: critical pions and diffusion in Model G

    Adrien Florio🇺🇸 · Eduardo Grossi🇮🇹 · Derek Teaney🇺🇸

    We present a detailed study of the finite momentum dynamics of the critical point of QCD, which lies in the dynamic universality class of Model G. The critical scaling of the model is analyzed in multiple dynamical channels. For instance, the finite momentum analysis allows us to precisely extract the pion dispersion curve below the critical point. The pion velocity is in striking agreement with the predictions relation and static universality. The pion damping rate and velocity are both consistent with the dynamical critical exponent of Model G. Similarly, although the critical amplitude for the diffusion coefficient of the conserved charges is small, it is clearly visible both in the restored phase and with finite explicit symmetry breaking, and its dynamical scaling is again consistent with . We determine a new set of universal dynamical critical amplitude ratios relating the diffusion coefficient to a suitably defined order parameter relaxation time. We also show that in a finite volume simulation, the chiral condensate diffuses on the coset manifold in a manner consistent with dynamical scaling, and with a diffusion coefficient that is determined by the transport coefficients of hydrodynamic pions. Finally, the amplitude ratios (together with other non-universal amplitudes also reported here) compile all relevant information for further studies of Model G both in and out of equilibrium.

    Comments:
    34 pages, 13 figures
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2306.06887 [pdf]
    PRD(2024)·25 citations

Affiliations

first authorsco-authorsvia INSPIRE