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Neutron Stars in Scalar-Tensor Theories: Analytic Scalar Charges and Universal Relations

ORAL

Abstract

Neutron stars are ideal astrophysical sources to probe general relativity due to their large compactnesses and strong gravitational fields. For example, binary pulsar and gravitational wave observations have placed stringent bounds on certain scalar-tensor theories in which a massless scalar field is coupled to the metric through matter. A remarkable phenomenon of neutron stars in such scalar-tensor theories is spontaneous scalarization, where a normalized scalar charge remains order unity even if the matter-scalar coupling vanishes asymptotically far from the neutron star. On the other hand, certain quasi-universal relations have been found for global quantities of neutron stars (such as the moment of inertia and quadrupole moment) that are insensitive to the underlying equations of state. While most works on scalarization of neutron stars focus on numerical analysis, we derive accurate scalar charges \textit{analytically}, providing ready-to-use expressions for scalar charges in massless scalar-tensor theories. We also find a new quasi-universal relation in these theories between the scalar charge and stellar binding energy (related to stellar compactness) and give mathematical support for this relation.

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Authors

  • Michael Stepniczka

    University of Virginia

  • Robert Grzywacz

    Moscow Institute of Physics and Technology, University of Virginia, California Institute of Technology, National High Magnetic Field Laboratory, University and Student Affairs; Oak Ridge Laboratory, Brookhaven National Laboratory, Physicist, Brookhaven National Laboratory, Oak Ridge National Laboratory, USA, Center for Nuclear Study, University of Tokyo, Advanced Science Research Center, Japan Atomic Energy Agency, Florida State University, Presidency University, Kolkata, INDIA, VECC,Kolkata, INDIA, SINP,Kolkata, INDIA, UGC-DAE CSR (Kolkata), INDIA, IFIN-HH, ELI-NP, Romania, Variable Energy Cyclotron Centre,Kolkata, INDIA, IEM, Kolkata, India, Victoria Institution (College), Kolkata, INDIA, Variable Energy Cyclotron Centre, Kolkata, INDIA, NHMFL; Florida State University, FAMU-FSU College of Engineering, Florida State University, Physics Department, Florida State University, Mississippi State University, NHMFL-FSU, U. Colorado at Boulder, NHMFL, University of Alabama at Birmingham, Oak Ridge National Laboratory, Argonne National Laboratory, Alabama School of Math and Science, University of South Alabama, University of Florida, University of Notre Dame, University of Texas at Dallas, Bob Jones University, University of Tennessee at Chattanooga, The Autonomous University of San Luis Potosí, Northern Arizona University, Flagstaff, AZ, Harvard-Smithsonian Center for Astrophysics, Cambridge, National Institute of Standards and Technology, Clemson University, University of South Florida, Phenikaa University, University of Ulsan, Ohio University, University of Hawaii, University of California, Davis, University of California, Davis., Saleh Research Centre, Department of Physics, Florida State university, Tallahassee, FL32306, USA, WestCHEM, School of Chemistry, University of Glasgow, Glasgow, G12 8QQ, UK, Professor, facility manager, Student, Florida State University(Former), Hebrew University, Israel \& Ioffe Institute, St.\ Petersburg, Russia, University of Tennessee, Knoxville