arXiv subjects

David Tsang

Publications and source records attributed to David Tsang.

At least 19 recordsLinked to original sources

arXiv2026

Measuring radii of merging neutron stars with interface-mode asteroseismology informed by nuclear theory and experiment

The structure and dynamics of neutron stars can be used to probe the physics of extreme matter at nuclear densities and beyond. Nucleonic matter up to ~2-3 times nuclear saturation density is well-studied by nuclear experiments and theoretical modelling. Matter beyond these densities may contain non-nucleonic degrees of freedom that determine the structure of the neutron star inner core and influence bulk observables like stellar radius. Neutron star radius is a key parameter for constraining the core equation of state, but is not a direct gravitational-wave observable during neutron star mergers. Here we show that, if nucleonic physics is well constrained at low densities, the frequency of the asteroseismic crust-core interface mode in a neutron star can be used to infer its radius to within 5-10%, in a way which is notably insensitive to the details of the inner core. This frequency can be measured through multimessenger coincident timing of resonant shattering flares, or direct observation of dynamical tidal resonance with next-generation gravitational-wave detectors. We show that improved constraints on low-density nucleonic physics by nuclear experimental and theoretical efforts will substantially improve such a radius measurement, leveraging low-density efforts for an improved understanding of physics at higher densities.

astro-ph.HE↗

arXiv2025

Dense Matter in Neutron Stars with eXTP

In this White Paper, we present the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission to constrain the equation of state of dense matter in neutron stars, exploring regimes not directly accessible to terrestrial experiments. By observing a diverse population of neutron stars - including isolated objects, X-ray bursters, and accreting systems - eXTP's unique combination of timing, spectroscopy, and polarimetry enables high-precision measurements of compactness, spin, surface temperature, polarimetric signals, and timing irregularity. These multifaceted observations, combined with advances in theoretical modeling, pave the way toward a comprehensive description of the properties and phases of dense matter from the crust to the core of neutron stars. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is planned to be launched in early 2030.

astro-ph.HE↗

arXiv2024

Resonant shattering flares as asteroseismic tests of chiral effective field theory

Chiral effective field theory ($\chi$EFT) has proved to be a powerful microscopic framework for predicting the properties of neutron-rich nuclear matter with quantified theoretical uncertainties up to about twice the nuclear saturation density. Tests of $\chi$EFT predictions are typically performed at low densities using nuclear experiments, with neutron star (NS) constraints only being considered at high densities. In this work, we discuss how asteroseismic quasi-normal modes within NSs could be used to constrain specific matter properties at particular densities, not just the integrated quantities to which bulk NS observables are sensitive. We focus on the crust-core interface mode, showing that measuring this mode's frequency would provide a meaningful test of $\chi$EFT at densities around half the saturation density. Conversely, we use nuclear matter properties predicted by $\chi$EFT to estimate that this mode's frequency is around 185 $\pm$ 50 Hz. Asteroseismic observables such as resonant phase shifts in gravitational-wave signals and multimessenger resonant shattering flare timings, therefore, have the potential to provide useful tests of $\chi$EFT.

astro-ph.HE↗

arXiv2024

Strengthening nuclear symmetry energy constraints using multiple resonant shattering flares of neutron stars with realistic mass uncertainties

With current and planned gravitational-wave (GW) observing runs, coincident multimessenger timing of Resonant Shattering Flares (RSFs) and GWs may soon allow for neutron star (NS) asteroseismology to be used to constrain the nuclear symmetry energy, an important property of fundamental nuclear physics that influences the composition and equation of state of NSs. In this work we examine the effects of combining multiple RSF detections on these symmetry energy constraints, and consider how realistic uncertainties in the masses of the progenitor NSs may weaken them. We show that the detection of subsequent multimessenger events has the potential to substantially improve constraints beyond those obtained from the first, and that this improvement is insensitive to the mass of the NSs which produce the RSFs and its uncertainty. This sets these asteroseismic constraints apart from bulk NS properties such as radius, for which the NS mass is highly important, meaning that any multimessenger RSF and GW events can equally improve our knowledge of fundamental physics.

astro-ph.HE↗

arXiv2022

Constraining Nuclear Symmetry Energy with Multi-messenger Resonant Shattering Flares

Much effort is devoted to measuring the nuclear symmetry energy through neutron star (NS) and nuclear observables. Since matter in the NS core may be non-hadronic, observables like radii and tidal deformability may not provide reliable constraints on properties of nucleonic matter. We demonstrate that coincident timing of a resonant shattering flare (RSF) and gravitational wave signal during binary NS inspiral probes the crust-core transition region and provides constraints on the symmetry energy comparable to terrestrial nuclear experiments. We show that nuclear masses, RSFs and measurements of NS radii and tidal deformabilities constrain different density ranges of the EOS, providing complementary probes.

astro-ph.HE↗

arXiv2022

Resonant Shattering Flares in Black Hole-Neutron Star and Binary Neutron Star Mergers

Resonant Shattering flares (RSFs) are bursts of gamma-rays expected to be triggered by tidal resonance of a neutron star (NS) during binary inspiral. They are strongly dependent on the magnetic field strength at the surface of the NS. By modelling these flares as being the result of multiple colliding relativistic shells launched during the resonance window, we find that the prompt non-thermal gamma-ray emission may have luminosity up to a few $\times10^{48}\text{ erg/s}$, and that a broad-band afterglow could be produced. We compute the expected rates of detectable RSFs using the BPASS population synthesis code, with different assumptions about the evolution of surface magnetic field strengths before merger. We find the rate of detectable RSFs to be $\sim 0.0001-5$ per year for BHNS mergers and $\sim 0.0005-25$ per year for NSNS mergers, with the lower bound corresponding to surface-field decay consistent with magneto-thermal evolution in purely crustal fields, while the upper bounds are for systems which have longer-lived surface magnetic fields supported by flux frozen into the superconducting core. If some of the observed SGRB precursor flares are indeed RSFs, this suggests the presence of a longer-lived surface field for some fraction of the neutron star population, and that we could expect RSFs to be the most common detectable EM counterpart to GW detections of BHNS mergers. The non-detection of a RSF prior to GRB170817A provides an upper bound on the magnetic fields of the progenitor NSs of $B_{\rm surf}\sim 10^{13.5} \text{ G}$.

astro-ph.HE↗

arXiv2021

Resonant Shattering Flares as Multimessenger Probes of the Nuclear Symmetry Energy

The behaviour of the nuclear symmetry energy near saturation density is important for our understanding of dense nuclear matter. This density dependence can be parameterised by the nuclear symmetry energy and its derivatives evaluated at nuclear saturation density. In this work we show that the core-crust interface mode of a neutron star is sensitive to these parameters, through the (density-weighted) shear-speed within the crust, which is in turn dependent on the symmetry energy profile of dense matter. We calculate the frequency at which the neutron star quadrupole ($\ell = 2$) crust-core interface mode must be driven by the tidal field of its binary partner to trigger a Resonant Shattering Flare (RSF). We demonstrate that coincident multimessenger timing of an RSF and gravitational wave chirp from a neutron star merger would enable us to place constraints on the symmetry energy parameters that are competitive with those from current nuclear experiments.

astro-ph.HE↗

arXiv2019

The Rate of Short Duration Gamma-Ray Bursts in the local Universe

The binary neutron star merger responsible for the gravitational wave event, GW170817, strengthened the merger association with short-duration gamma-ray bursts (SGRBs) following the detection of the SGRB counterpart, GRB 170817A. Here we consider the constraints on a population of local gamma-ray bursts with moderately short duration ($T_{90}<4 \textrm{ s}$) and within $d < 200 \textrm{ Mpc}$, that may have originated from similar compact binary mergers. Using well localised gamma-ray bursts from $\sim14.5 \textrm{ years}$ of Swift/Burst Alert Telescope monitoring, we find no events with high likelihood of being in this distance range, and place an upper limit for the all-sky rate of such events of $<4\ \textrm{y}^{-1}$. For Fermi/Gamma-ray Burst Monitor (GBM) and CGRO/Burst And Transient Source Experiment (BATSE) detected bursts, where the localisation has considerably larger uncertainties, we cross-correlated with 2MASS Redshift Survey galaxies at $d<100 \textrm{ Mpc}$, obtaining a weaker constraint of $< 12\ \textrm{y}^{-1}$. A separate correlation search from the GBM and BATSE bursts for giant flares originating from soft gamma-ray repeaters in nearby galaxies ($d < 11 \textrm{ Mpc} $ ) yields an upper limit of $<3\ \textrm{y}^{-1}$.

astro-ph.HE↗

arXiv2018

Dense matter with eXTP

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

astro-ph.HE↗

arXiv2018

The Rate of Short-Duration Gamma-Ray Bursts in the Local Universe

Following the faint gamma-ray burst, GRB 170817A, coincident with a gravitational wave-detected binary neutron star merger at $d\sim40$ Mpc, we consider the constraints on a local population of faint short duration GRBs (defined here broadly as $T_{90}<4$ s). We review proposed low-redshift short-GRBs and consider statistical limits on a $d\lessapprox200$ Mpc population using Swift/Burst Alert Telescope (BAT), Fermi/Gamma-ray Burst Monitor (GBM), and Compton Gamma-Ray Observatory (CGRO) Burst and Transient Source Experiment (BATSE) GRBs. Swift/BAT short-GRBs give an upper limit for the all-sky rate of $<4$ y$^{-1}$ at $d<200$ Mpc, corresponding to $<5$% of SGRBs. Cross-correlation of selected CGRO/BATSE and Fermi/GBM GRBs with $d<100$ Mpc galaxy positions returns a weaker constraint of $\lessapprox12\ {\rm y^{-1}}$. A separate search for correlations due to SGR giant flares in nearby ($d<11$ Mpc) galaxies finds an upper limit of $<3\ {\rm y^{-1}}$. Our analysis suggests that GRB 170817A-like events are likely to be rare in existing SGRB catalogues. The best candidate for an analogue remains GRB 050906, where the Swift/BAT location was consistent with the galaxy IC0327 at $d\approx132$ Mpc. If binary neutron star merger rates are at the high end of current estimates, then our results imply that at most a few percent will be accompanied by detectable gamma-ray flashes in the forthcoming LIGO/Virgo science runs.

astro-ph.HE↗

arXiv2017

Electromagnetic Chirps from Neutron Star-Black Hole Mergers

We calculate the electromagnetic signal of a gamma-ray flare coming from the surface of a neutron star shortly before merger with a black hole companion. Using a new version of the Monte Carlo radiation transport code Pandurata that incorporates dynamic spacetimes, we integrate photon geodesics from the neutron star surface until they reach a distant observer or are captured by the black hole. The gamma-ray light curve is modulated by a number of relativistic effects, including Doppler beaming and gravitational lensing. Because the photons originate from the inspiraling neutron star, the light curve closely resembles the corresponding gravitational waveform: a chirp signal characterized by a steadily increasing frequency and amplitude. We propose to search for these electromagnetic chirps using matched filtering algorithms similar to those used in LIGO data analysis.

astro-ph.HE↗

arXiv2015

Self-Trapping of Diskoseismic Corrugation Modes in Neutron Star Spacetimes

We examine the effects of higher-order multipole contributions of rotating neutron star (NS) spacetimes on the propagation of corrugation (c-)modes within a thin accretion disk. We find that the Lense-Thirring precession frequency, which determines the propagation region of the low-frequency fundamental corrugation modes, can experience a turnover allowing for c-modes to become self-trapped for sufficiently high dimensionless spin $j$ and quadrupole rotational deformability $α$. If such self-trapping c-modes can be detected, e.g. through phase-resolved spectroscopy of the iron line for a high-spin low-mass accreting neutron star, this could potentially constrain the spin-induced NS quadrupole and the NS equation of state.

astro-ph.HE↗

arXiv2015

Slimplectic Integrators: Variational Integrators for General Nonconservative Systems

Symplectic integrators are widely used for long-term integration of conservative astrophysical problems due to their ability to preserve the constants of motion; however, they cannot in general be applied in the presence of nonconservative interactions. In this Letter, we develop the "slimplectic" integrator, a new type of numerical integrator that shares many of the benefits of traditional symplectic integrators yet is applicable to general nonconservative systems. We utilize a fixed time-step variational integrator formalism applied to the principle of stationary nonconservative action developed in Galley, 2013; Galley, Tsang & Stein, 2014. As a result, the generalized momenta and energy (Noether current) evolutions are well-tracked. We discuss several example systems, including damped harmonic oscillators, Poynting-Robertson drag, and gravitational radiation reaction, by utilizing our new publicly available code to demonstrate the slimplectic integrator algorithm. Slimplectic integrators are well-suited for integrations of systems where nonconservative effects play an important role in the long-term dynamical evolution. As such they are particularly appropriate for cosmological or celestial N-body dynamics problems where nonconservative interactions, e.g. gas interactions or dissipative tides, can play an important role.

astro-ph.IM↗

arXiv2014

The principle of stationary nonconservative action for classical mechanics and field theories

We further develop a recently introduced variational principle of stationary action for problems in nonconservative classical mechanics and extend it to classical field theories. The variational calculus used is consistent with an initial value formulation of physical problems and allows for time-irreversible processes, such as dissipation, to be included at the level of the action. In this formalism, the equations of motion are generated by extremizing a nonconservative action $\mathcal{S}$, which is a functional of a doubled set of degrees of freedom. The corresponding nonconservative Lagrangian contains a potential $K$ which generates nonconservative forces and interactions. Such a nonconservative potential can arise in several ways, including from an open system interacting with inaccessible degrees of freedom or from integrating out or coarse-graining a subset of variables in closed systems. We generalize Noether's theorem to show how Noether currents are modified and no longer conserved when $K$ is non-vanishing. Consequently, the nonconservative aspects of a physical system are derived solely from $K$. We show how to use the formalism with examples of nonconservative actions for discrete systems including forced damped harmonic oscillators, radiation reaction on an accelerated charge, and RLC circuits. We present examples for nonconservative classical field theories. Our approach naturally allows for irreversible thermodynamic processes to be included in an unconstrained variational principle. We present the nonconservative action for a Navier-Stokes fluid including the effects of viscous dissipation and heat diffusion, as well as an action that generates the Maxwell model for viscoelastic materials, which can be easily generalized to more realistic rheological models. We show that the nonconservative action can be derived as the classical limit of a more complete quantum theory.

math-ph↗

arXiv2014

Linear Corotation Torques in Non-Barotropic Disks

I derive a fully analytic expression for the linear corotation torque to first order in eccentricity for planets in non-barotropic protoplanetary disks, taking into account the effect of disk entropy gradients. This torque formula is applicable to both the co-orbital corotation torque and the non co-orbital corotation torques -- for planets in orbits with non-zero eccentricity -- in disks where the thermal diffusivity and viscosity are sufficient to maintain linearity of these interactions. While the co-orbital corotation torque is important for migration of planets in Type I migration, the non co-orbital corotation torque plays an important role in the eccentricity evolution of giant planets that have opened gaps in the disk. The presence of an entropy gradient in the disk can significantly modify the corotation torque in both these cases.

astro-ph.EP↗

arXiv2014

Shedding Light on the Eccentricity Valley: Gap Heating and Eccentricity Excitation of Giant Planets in Protoplanetary Disks

We show that the first order (non co-orbital) corotation torques are significantly modified by entropy gradients in a non-barotropic protoplanetary disk. Such non-barotropic torques can dramatically alter the balance that, for barotropic cases, results in the net eccentricity damping for giant gap-clearing planets embedded in the disk. We demonstrate that stellar illumination can heat the gap enough for the planet's orbital eccentricity to instead be excited. We also discuss the "Eccentricity Valley" noted in the known exoplanet population, where low-metallicity stars have a deficit of eccentric planets between $\sim 0.1$ and $\sim 1$ AU compared to metal-rich systems (Dawson & Murray-Clay 2013). We show that this feature in the planet distribution may be due to the self-shadowing of the disk by a rim located at the dust sublimation radius $\sim 0.1$ AU, which is known to exist for several T Tauri systems. In the shadowed region between $\sim 0.1$ and $\sim 1$ AU lack of gap insolation allows disk interactions to damp eccentricity. Outside such shadowed regions stellar illumination can heat the planetary gaps and drive eccentricity growth for giant planets. We suggest that the self-shadowing does not arise at higher metallicity due to the increased optical depth of the gas interior to the dust sublimation radius.

astro-ph.EP↗

arXiv2013

Traversable Achronal Retrograde Domains In Spacetime

There are many spacetime geometries in general relativity which contain closed timelike curves. A layperson might say that retrograde time travel is possible in such spacetimes. To date no one has discovered a spacetime geometry which emulates what a layperson would describe as a time machine. The purpose of this paper is to propose such a space-time geometry. In our geometry, a bubble of curvature travels along a closed trajectory. The inside of the bubble is Rindler spacetime, and the exterior is Minkowski spacetime. Accelerating observers inside of the bubble travel along closed timelike curves. The walls of the bubble are generated with matter which violates the classical energy conditions. We refer to such a bubble as a Traversable Achronal Retrograde Domain In Spacetime.

gr-qc↗

arXiv2013

The Blue Box White Paper

This white paper is an explanation of Ben and Dave's TARDIS time machine, written for laypeople who are interested in time travel, but have no technical knowledge of Einstein's Theory of General Relativity. The first part of this paper is an introduction to the pertinent ideas from Einstein's theory of curved spacetime, followed by a review of other popular time machine spacetimes. We begin with an introduction to curvature and lightcones. We then explain the Alcubierre Warp Drive, the Morris-Thorne wormhole, and the Tipler cylinder. We then describe the Traversable Achronal Retrograde Domain in Spacetime (TARDIS), and explain some of its general properties. Our TARDIS is a bubble of spacetime curvature which travels along a closed loop in space and time. A person travelling within the bubble will feel a constant acceleration. A person outside of the TARDIS will see two bubbles: one which is evolving forwards in time, and one which is evolving backwards in time. We then discuss the physical limitations which may prevent us from ever constructing a TARDIS. Finally, we discuss the method through which a TARDIS can be used to travel between arbitrary points in space and time, and the possible dangers involved with exiting a TARDIS from the wrong side. Before we begin, would you like a Jelly Baby?

physics.pop-ph↗