A characteristic observational signature of cosmic strings are short duration gravitational wave (GW) bursts. These have been searched for by the LIGO-Virgo-KAGRA (LVK) collaboration, and will be searched for with LISA. We point out that these burst signals are repeated, since cosmic string loops evolve quasi-periodically in time, and will always appear from essentially the same position in the sky. We estimate the number of GW repeaters for LVK and LISA, and show that the string tension that can be probed scales as detector sensitivity to the sixth power, which raises hope for detection in future GW detectors. The observation of repeated GW bursts from the same cosmic string loop helps distinguish between the GW waveform parameters and the sky-localization.
We explore the possibility that Fast Radio Bursts are due to the annihilation of cusps on cosmic string loops. We compute the energy released in the annihilation events in the radio region, the expected event rate, and the time scale of the bursts. We find that the energy and event rates are sufficiently high and the time scale is sufficiently small to explain the current data. We predict how the event rate will change as the resolution of telescopes improves. Since the burst rate depends on the string tension, future data will allow the determination of the tension.
We explore the kinematical effect of having extra dimensions on the gravity wave emission from cosmic strings. Additional dimensions both round off cusps, and reduce the probability of their formation. We recompute the gravity wave burst, taking into account these two factors, and find a potentially significant damping on the gravity waves of the strings.
The high-redshift gamma-ray bursts (GRBs), GRBs 080913 and 090423, challenge the conventional GRB progenitor models by their short durations, typical for short GRBs, and their high energy releases, typical for long GRBs. Meanwhile, the GRB rate inferred from high-redshift GRBs also remarkably exceeds the prediction of the collapsar model, with an ordinary star formation history. We show that all these contradictions could be eliminated naturally, if we ascribe some high-redshift GRBs to electromagnetic bursts of superconducting cosmic strings. High-redshift GRBs could become a reasonable way t…
Cusps of cosmic strings emit strong beams of high-frequency gravitational waves (GW). As a consequence of these beams, the stochastic ensemble of gravitational waves generated by a cosmological network of oscillating loops is strongly non Gaussian, and includes occasional sharp bursts that stand above the rms GW background. These bursts might be detectable by the planned GW detectors LIGO/VIRGO and LISA for string tensions as small as $G μ\sim 10^{-13}$. The GW bursts discussed here might be accompanied by Gamma Ray Bursts.
We analyze the gravitational wave signatures of a network of metastable cosmic strings. We consider the case of cosmic string instability to breakage, with no primordial population of monopoles. This scenario is well motivated from GUT and string theoretic models with an inflationary phase below the GUT/string scale. The network initially evolves according to a scaling solution, but with breakage events resulting from confined monopoles (beads) being pair produced and accelerated apart. We find these ultra-relativistic beads to be a potent source of gravitational waves bursts, detectable by In…
Galactic nuclei are densely populated by stellar mass compact objects such as black holes and neutron stars. Bound, highly eccentric binaries form as a result of gravitational wave (GW) losses during close flybys between these objects. We study the evolution of these systems using 2.5 and 3.5 order post-Newtonian equations of motion. The GW signal consists of many thousand repeated bursts (RB) for minutes to days (depending on the impact parameter and masses), followed by a powerful GW chirp and an eccentric merger. We show that a significant signal to noise ratio (SNR) accumulates already in …
We investigate the behavior of classical closed strings in a gravitational wave burst and discover an intriguing resonant behavior where the energy absorbed by the strings is crucially dependent on the amplitude and frequency of the gravitational wave. This behavior can be traced to the well-known behavior of the solutions to the Mathieu equation.
Superconducting cosmic strings may be able to power energetic gamma-ray bursts, in particular at high-redshifts ($z>6$). The ultra-relativistic outflows driven by the superconducting cosmic strings, however, seem too narrow to be consistent with the afterglow data of GRB 090423 and GRB 080913.
We study the relative contribution of cusps and pseudocusps, on cosmic (super)strings, to the emitted bursts of gravitational waves. The gravitational wave emission in the vicinity of highly relativistic points on the string follows, for a high enough frequency, a logarithmic decrease. The slope has been analytically found to be $^{-4}/_3$ for points reaching exactly the speed of light in the limit $c=1$. We investigate the variations of this high frequency behaviour with respect to the velocity of the points considered, for strings formed through a numerical simulation, and we then compute nu…
Compact object binaries formed from dynamics interactions will generically have non-zero orbital eccentricity. The gravitational waves from such binaries can change drastically depending on how large the eccentricity is, ranging from emitted in small a subset of orbital harmonics at low eccentricities, to being concentrated into intense bursts of radiation from each pericenter passage at large eccentricities. Gravitational waves from such highly eccentric binaries present themselves an intriguing systems for probing fundamental physics, but also present interesting challenges in terms of detec…
Cusps of superconducting strings can serve as GRB engines. A powerful beamed pulse of electromagnetic radiation from a cusp produces a jet of accelerated particles, whose propagation is terminated by the shock responsible for GRB. A single free parameter, the string scale of symmetry breaking $η\sim 10^{14} GeV$, together with reasonable assumptions about the magnitude of cosmic magnetic fields and the fraction of volume that they occupy, explains the GRB rate, duration and fluence, as well as the observed ranges of these quantities. The wiggles on the string can drive the short-time structure…
In this article we update constraints on superconducting cosmic strings (SCSs) in light of the recent observational developments of fast radio bursts (FRBs) astronomy. Assuming strings follow an exponential distribution characterized by current, we show that two parameters in our context, which are the characteristic tension ($Gμ$) and a parameter which describes the aforementioned exponential distribution ($I_c$), can be constrained by FRB experiments. Particularly, we investigate data sets from Parkes and ASKAP. We looked through a parameter space where $Gμ\sim [10^{-17}, 10^{-12}]$ and $I_c…
The emission of axions from supernovae is an interesting possibility to account for the Gamma-Ray Bursts provided their energy can be effectively converted into electromagnetic energy elsewhere. The connection between supernova and gamma-ray bursts has been recently confirmed by the observed correlation between the burst of April 25, 1998 and the supernova SN1998bw. We argue that the axion convertion into photons can be more efficient if one considers the coupling between an intermediate scale axion and the string theory dilaton along with the inclusion of string loops. We also discuss the way…
The GRB outflow driven by superconducting cosmic strings is likely to be an arc rather than a usually-considered spherical cap. In such a case, the afterglows of the cosmic string GRBs could be basically consistent with the observation of the high-redshift GRBs.
Highly beamed, short-duration electromagnetic bursts could be produced by superconducting cosmic string (SCS) loops oscillating in cosmic magnetic fields. We demonstrated that the basic characteristics of SCS bursts such as the electromagnetic frequency and the energy release could be consistently exhibited in the recently discovered fast radio bursts (FRBs). Moreover, it is first showed that the redshift distribution of the FRBs can also be well accounted for by the SCS burst model. Such agreements between the FRBs and SCS bursts suggest that the FRBs could originate from SCS bursts and thus …
Cosmic strings are potential gravitational wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes PTA data. We find four events with a false alarm probability less than 1%. However further investigation shows that all of these are likely to be spurious. As there are no convincing detections we place upper limits on the GW amplitude for different event durations. From these bounds we place limits on the cosmic string tension of G mu ~ 10^{-5}, and highlight that this…
Recent studies of scalar and gravitational waveforms from high-eccentricity, extreme mass-ratio black hole binaries show the presence of quasi-normal bursts (QNB) -- lingering high frequency decaying oscillations (also known as ``wiggles'') -- soon after each periapsis passage. One puzzle associated with these QNB is that in the case of a nearly-extreme rotating central black hole the frequency of the QNB has been found to be in a range which is lower than the corresponding range of relevant quasi-normal modes. We reproduce these results using a different approach and perform a detailed analys…
A variety of gravitational-wave transient sources can be modeled in the Fourier domain using a power law. This simple power-law model provides a reasonable approximation for gravitational-wave bursts from cosmic string cusps, cosmic string kinks, and the memory effect. Each of these sources is described using a different spectral index. In this work, we simulate interferometer strain data with injections of power-law and memory bursts to demonstrate parameter estimation, signal detection, and model selection. We show how Bayesian inference can be used to measure the power-law spectral index, t…
Previous studies on high-energy gamma-ray burst neutrinos from IceCube suggest a neutrino speed variation at the Lorentz violation~(LV) scale of $\sim 6.4\times 10^{17}$~GeV, with opposite velocity variances between neutrinos and antineutrinos. Within a space-time foam model, inspired by string theory, we develop an approach to describe the suggested neutrino/antineutrino propagation properties with both Lorentz invariance and CPT symmetry breaking. A threshold analysis on the bremsstrahlung of electron-positron pair~($ν\rightarrowνee^{+}$) for the superluminal~(anti)neutrino is performed. We …
In this paper we calculate the radio burst signals from three kinds of structures of superconducting cosmic strings. By taking into account the observational factors including scattering and relativistic effects, we derive the event rate of radio bursts as a function of redshift with the theoretical parameters $Gμ$ and $\mathcal{I}$ of superconducting strings. Our analyses show that cusps and kinks may have noticeable contributions to the event rate and in most cases cusps would dominate the contribution, while the kink-kink collisions tend to have secondary effects. By fitting theoretical pre…
The strong beams of high-frequency gravitational waves (GW) emitted by cusps and kinks of cosmic strings are studied in detail. As a consequence of these beams, the stochastic ensemble of GW's generated by a cosmological network of oscillating loops is strongly non Gaussian, and includes occasional sharp bursts that stand above the ``confusion'' GW noise made of many smaller overlapping bursts. Even if only 10% of all string loops have cusps these bursts might be detectable by the planned GW detectors LIGO/VIRGO and LISA for string tensions as small as $G μ\sim 10^{-13}$. In the implausible ca…
A network of observable, macroscopic cosmic (super-)strings may have formed in the early universe. If so, the cusps that generically develop on cosmic-string loops emit bursts of gravitational radiation that could be detectable by both ground- and space-based gravitational-wave interferometers. Here we report on two versions of a LISA-oriented string-burst search pipeline that we have developed and tested within the context of the Mock LISA Data Challenges. The two versions rely on the publicly available MultiNest and PyMC software packages, respectively. To reduce the effective dimensionality…
Berezinsky, Hnatyk and Vilenkin showed that superconducting cosmic strings could be central engines for cosmological gamma-ray bursts and for producing the neutrino component of ultra-high energy cosmic rays. A consequence of this mechanism would be that a detectable cusp-triggered gravitational wave burst should be released simultaneously with the $γ$-ray surge. If contemporary measurements of both $γ$ and $ν$ radiation could be made for any particular source, then the cosmological time-delay between them might be useful for putting unprecedently tight bounds on the neutrino mass spectrum. Su…
The gravitational wave (GW) signals emitted by a network of cosmic strings are reexamined in view of the possible formation of a network of cosmic superstrings at the end of brane inflation. The reconnection probability $p$ of intersecting fundamental or Dirichlet strings might be much smaller than 1, and the properties of the resulting string network may differ significantly from those of ordinary strings (which have $p=1$). In addition, it has been recently suggested that the typical length of newly formed loops may differ by a factor $ε\ll 1$ from its standard estimate. Here, we analyze the…
Junctions on cosmic string loops give rise to the proliferation of sharp kinks. We study the effect of this proliferation on the gravitational wave (GW) signals emitted from string networks with junctions, assuming a scaling solution. We calculate the rate of occurrence and the distribution in amplitude of the GW bursts emitted at cusps and kinks in the frequency bands of LIGO and LISA as a function of the string tension, the number of sharp kinks on loops with junctions and the fraction of loops in the cosmological network which have junctions. Combining our results with current observational…
We discuss data analysis techniques that can be used in the search for gravitational wave bursts from cosmic strings. When data from multiple interferometers are available, we describe consistency checks that can be used to greatly reduce the false alarm rates. We construct an expression for the rate of bursts for arbitrary cosmic string loop distributions and apply it to simple known solutions. The cosmology is solved exactly and includes the effects of a late-time acceleration. We find substantially lower burst rates than previous estimates suggest and explain the disagreement. Initial LIGO …
We consider the femto-lensing due to a cosmic string. If a cosmic string with the deficit angle $Δ\sim 100$ [femto-arcsec] $\sim10^{-18}$ [rad] exists around the line of sight to a gamma-ray burst, we may observe characteristic interference patterns caused by gravitational lensing in the energy spectrum of the gamma-ray burst. This "femto-lensing" event was first proposed as a tool to probe small mass primordial black holes. In this paper, we propose use of the femto-lensing to probe cosmic strings with extremely small tension. Observability conditions and the event rate are discussed. Differe…
We consider the problem of characterisation of burst sources detected with the Laser Interferometer Space Antenna (LISA) using the multi-modal nested sampling algorithm, MultiNest. We use MultiNest as a tool to search for modelled bursts from cosmic string cusps, and compute the Bayesian evidence associated with the cosmic string model. As an alternative burst model, we consider sine-Gaussian burst signals, and show how the evidence ratio can be used to choose between these two alternatives. We present results from an application of MultiNest to the last round of the Mock LISA Data Challenge, …
We investigate the effect of a large number of kinks on the gravitational power radiated by cosmic string loops. We show that the total power radiated by a loop with N left-moving and right-moving kinks is proportional to N and increases with the typical kink angle. We then apply these results to loops containing junctions which give rise to a proliferation of the number of sharp kinks. We show that the time of gravitational decay of these loops is smaller than previously assumed. In light of this we revisit the gravitational wave burst predictions from a network containing such loops. We find…
Cusps of superconducting strings can serve as GRB engines. A powerful beamed pulse of electromagnetic radiation from a cusp produces a jet of accelerated particles, whose propagation is terminated by the shock responsible for GRB. A single free parameter, the string scale of symmetry breaking $η\sim 10^{14} GeV$, together with reasonable assumptions about the magnitude of cosmic magnetic fields and the fraction of volume that they occupy, explains the GRB rate, duration and fluence, as well as the observed ranges of these quantities. The wiggles on the string can drive the short-time structure…
We report development of a code to calculate the scalar self-force on a scalar-charged particle moving on generic bound orbits in the Kerr spacetime. The scalar self-force model allows rapid development of computational techniques relevant to generic gravitational extreme-mass-ratio inspirals (EMRIs). Our frequency-domain calculations are made with arbitrary numerical precision code written in \textsc{Mathematica}. We extend spectral source integration techniques to the Kerr spacetime, increasing computational efficiency. We model orbits with nearly arbitrary inclinations $0\leqι<π/2$ and ecce…
Multi-Band Constraints on Cosmic Strings: Unifying Harmonic and Burst Spectra
International Centre for Theoretical Physics Asia-Pacific (ICTP-AP)（亚太理论物理中心）；University of Chinese Academy of Sciences (UCAS)（中国科学院大学）；Taiji Laboratory for Gravitational Wave Universe（太极引力波宇宙实验室）；King’s College London, University of London（伦敦大学国王学院）；University of Florida（佛罗里达大学）；University of Notre Dame（圣母大学）；Johannes Gutenberg-Universität Mainz（美因茨约翰内斯古腾堡大学）；The Hong Kong University of Science and Technology（香港科技大学）
We outline a model of abelian-Higgs strings with variable scalar and vector core radii. In general, the functions determining the time and position-dependent core widths may be expressed as arbitrary left or right movers, of which the usual constant values are a particular solution. In this case the string may carry momentum, even if the embedding of its central axis remains fixed, and the resulting objects resemble "necklaces". Some possible astrophysical applications of lumpy strings, including as potential engines for anomalous gamma ray bursts, are also discussed.
Gravitational waves (GWs) are one of the key signatures of cosmic strings. If GWs from cosmic strings are detected in future experiments, not only their existence can be confirmed but also their properties might be probed. In this paper, we study the determination of cosmic string parameters through direct detection of GW signatures in future ground-based GW experiments. We consider two types of GWs, bursts and the stochastic GW background, which provide us with different information about cosmic string properties. Performing the Fisher matrix calculation on the cosmic string parameters, such …
We calculate the gravitational radiation emitted by an infinite cosmic string with two oppositely moving wave-trains, in the small amplitude approximation. After comparing our result to the previously studied cases we extend the results to a new regime where the wavelengths of the opposing wave-trains are very different. We show that in this case the amount of power radiated vanishes exponentially. This means that small excitations moving in only one direction may be very long lived, and so the size of the smallest scales in a string network might be much smaller than what one would expect fro…
We do a complete calculation of the stochastic gravitational wave background to be expected from cosmic strings. We start from a population of string loops taken from simulations, smooth these by Lorentzian convolution as a model of gravitational back reaction, calculate the average spectrum of gravitational waves emitted by the string population at any given time, and propagate it through a standard model cosmology to find the stochastic background today. We take into account all known effects, including changes in the number of cosmological relativistic degrees of freedom at early times and …
Gravitational wave bursters are sources which emit repeatedly bursts of gravitational waves, and have been recently suggested as potentially interesting candidates for gravitational wave (GW) detectors. Mechanisms that could give rise to a GW burster can be found for instance in highly magnetized neutron stars (the magnetars which explain the phenomenon of soft gamma repeaters), in accreting neutron stars and in hybrid stars with a quark core. We point out that these sources have very distinctive experimental signatures. In particular, as already observed in the gamma-ray bursts from soft gamm…
Cosmic strings are predicted to form kinks and cusps that travel along the string at close to the speed of light. These disturbances are radiated away as highly beamed gravitational waves that produce a burst like pulse as the cone of emission sweeps past an observer. Gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA) and the Laser Interferometer Gravitational wave Observatory (LIGO) will be capable of detecting these bursts for a wide class of string models. Such a detection would illuminate the fields of string theory, cosmology, and relativity. Here we develo…
Since their serendipitous discovery, Fast Radio Bursts (FRBs) have garnered a great deal of attention from both observers and theorists. A new class of radio telescopes with wide fields of view have enabled a rapid accumulation of FRB observations, confirming that FRBs originate from cosmological distances. The high occurrence rate of FRBs and the development of new instruments to observe them create opportunities for FRBs to be utilized for a host of astrophysical and cosmological studies. We focus on the rare, and as yet undetected, subset of FRBs that undergo repeated bursts and are strongl…
Aims: Recently, cosmological fast radio bursts (FRBs) have been used to provide the most stringent limit up to date on Einstein's Equivalence Principle (EEP). We study how to further test EEP with FRBs. Methods: Future systematic radio surveys will certainly find abundant FRBs at cosmological distances and some of them will inevitably be located behind clusters of galaxies. Here we suggest to use those FRBs to further test EEP. Results: We find that the robustness and accuracy of testing EEP can be improved further by orders of magnitude with these FRBs. The same methodology can also be applie…
We here present the first analytic effective fly-by (EFB) waveforms designed to accurately capture the burst of gravitational radiation from the closest approach of highly eccentric compact binaries. The waveforms are constructed by performing a re-summation procedure on the well-known Fourier series representation of the two-body problem at leading post-Newtonian order. This procedure results in two models: one in the time-domain, and one in the Fourier domain, which makes use of the stationary phase approximation. We discuss the computational efficiency of these models, and find that the tim…
I study a relativistic open string coupling through its endpoints to a plane wave with arbitrary temporal profile. The string's transverse oscillations respond linearly to the external field. This makes it possible to solve the classical equations, and to calculate the quantum-mechanical S-matrix in closed form. I analyze the dynamics of the string as the characteristic frequency and duration of the pulse are continuously varied. I derive, in particular, the multipole expansion in the adiabatic limit of very long wavelengths, and discuss also more violent phenomena such as shock waves, cusps a…
We discuss the possibility that galactic gravitational wave sources might give burst signals at a rate of several events per year, detectable by state-of-the-art detectors. We are stimulated by the results of the data collected by the EXPLORER and NAUTILUS bar detectors in the 2001 run, which suggest an excess of coincidences between the two detectors, when the resonant bars are orthogonal to the galactic plane. Signals due to the coalescence of galactic compact binaries fulfill the energy requirements but are problematic for lack of known candidates with the necessary merging rate. We examine…
A tiny fraction of observed gamma-ray bursts (GRBs) may be lensed. The time delays induced by the gravitational lensing are milliseconds to seconds if the point lenses are intermediate-mass black holes. The prompt emission of the lensed GRBs, in principle, should have repeated pulses with identical light curves and spectra but different fluxes and slightly offset positions. In this work, we search for such candidates within the GRBs detected by Fermi/GBM, Swift/BAT, and HXMT/HE and report the identification of an attractive event GRB 200716C that consists of two pulses. Both the autocorrelatio…
We present the results obtained from an all-sky search for gravitational-wave (GW) bursts in the 64-2000 Hz frequency range in data collected by the LIGO detectors during the first year (November 2005 - November 2006) of their fifth science run. The total analyzed livetime was 268.6 days. Multiple hierarchical data analysis methods were invoked in this search. The overall sensitivity expressed in terms of the root-sum-square (rss) strain amplitude h_{rss} for gravitational-wave bursts with various morphologies was in the range of 6 times 10^{-22} Hz^{-1/2} to a few times 10^{-21} Hz^{-1/2}. No…
We study the gravitational radiation from a rotating monopole-antimonopole pair connected by a string. While at not too high frequencies the emitted gravitational spectrum is described asymptotically by $P_n\propto n^{-1}$, the spectrum is exponentially suppressed in the high-frequency limit, $P_n\propto \exp(-n/n_{\rm cr})$. Below $n_{\rm cr}$, the emitted spectrum of gravitational waves is very similar to the case of an oscillating monopole pair connected by a string, and we argue therefore that the spectrum found holds approximately for any moving monopole-string system. As application, we …
