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Harald P. Pfeiffer

Publications and source records attributed to Harald P. Pfeiffer.

At least 19 recordsLinked to original sources

Enabling gravitational-wave astronomy with spin-precessing black holes on generic orbits

Binary black holes (BBHs) formed in dense stellar environments or in hierarchical triples can coalesce on eccentric orbits and carry spins of arbitrary orientation, leaving distinctive imprints on their gravitational-wave (GW) emission. We present SEOBNRv6EPHM: the first generic-orbit, spin-precessing model in the effective-one-body SEOBNR family, whose waveforms have underpinned LIGO-Virgo GW analyses since 2011. The model describes the dynamics and multipolar GW signal of generic BBHs, covering the inspiral-merger-ringdown of coalescing binaries and extending to dynamical captures and scattering encounters. We perform the first systematic accuracy assessment of a generic-orbit model against numerical relativity (NR) waveforms of spin-precessing BBHs, using 1437 quasi-circular (QC) and 87 eccentric simulations: median waveform mismatches remain below $1 \%$, matching the accuracy of the QC model SEOBNRv5PHM, and improving on the state-of-the-art generic-orbit model TEOBResumS-Dalí by a median factor of $ 4 $. The model also reproduces the non-perturbative phenomenology observed in NR simulations of generic-spin BBH scattering. It is $\sim 2 - 3$ times faster than SEOBNRv5PHM in the QC limit, and up to an order of magnitude faster than TEOBResumS-Dalí, bringing eccentric inference to the cost of current QC analyses. As a proof of principle, we analyze eleven GW events and focus on GW200129, strengthening its evidence for eccentricity $-$ a result supported by injection-recovery studies with synthetic NR signals of eccentric, spin-precessing BBHs. SEOBNRv6EPHM thus enables, for the first time, accurate and efficient GW analyses that jointly account for eccentricity and spin precession.

gr-qc

Towards long and accurate numerical relativity waveforms of binary black holes beyond general relativity

Numerical relativity (NR) simulations of compact binaries in theories beyond general relativity (GR) will be pivotal for the continued development of future tests of gravity with gravitational waves (GWs). In this Letter, we show that the combination of spectral methods and the "fixing-the-equations" approach allows us to produce the longest waveforms in the literature for a genuine beyond-GR theory, thus bringing NR methods for alternative theories of gravity closer to the state-of-the-art in GR. For concreteness, we focus on the well-known shift-symmetric version of scalar Gauss-Bonnet gravity, a theory postulating the existence of an additional dynamical scalar and describing black holes (BHs) different from the Kerr solution. We extract the gravitational and scalar waveforms at future null infinity for equal-mass, nonspinning, eccentricity-reduced BH binaries, and quantify the phase errors to be $\lesssim$ 1 rad after 40+ GW cycles (20+ orbits). We also show that the GW phase corrections in this alternative theory are distinguishable from Einstein's theory and lead to an earlier coalescence time than in GR. Obtaining such waveforms is a stepping stone to perform precise comparisons with Post-Newtonian theory and to calibrate waveform models beyond GR.

gr-qc

High-accuracy drivers to simulate black hole binaries beyond general relativity with the fixing-the-equations approach

We implement the "fixing-the-equations" approach [Phys.Rev.D 96 (2017) 8, 084043] in spectre, an NR code using a pseudo-spectral discontinuous Galerkin scheme, to produce long and accurate NR waveforms in the well-known shift-symmetric version of scalar Gauss-Bonnet (sGB) gravity. To achieve this, we introduce a new family of comoving driver equations that exploits the approximate symmetries of quasicircular binary systems and is designed to recover the exact (quasi-)stationary solutions of the fully-coupled theory. We validate our single black hole (BH) solutions against analytic predictions and show that, even for binary BHs in the early inspiral, the intrinsic BH quantities are relatively insensitive to the timescales entering the driver equation. Attention is given to the prescription of driver equations for tensors, for which we give an example of how treating tensor components as scalars can lead to undesired behaviour over long timescales, including spurious growth of the BH spins. A more appropriate generalization to the tensor case is given for the comoving driver, which is shown to avoid these issues. Overall, our implementation leverages state-of-the-art methods for eccentricity reduction and wave extraction with Cauchy Characteristic Evolution to simulate systems with eccentricity $\lesssim 10^{-3}$. We obtain waveforms with phase errors $\lesssim \mathcal{O}(1) \, \mathrm{rad}$ over almost 40 GW-cycles, which naturally incorporate memory contributions.

gr-qc

Chase Orbits, not Time: A Scalable Paradigm for Long-Duration Eccentric Gravitational-Wave Surrogates

Orbital eccentricity is a key tracer of the astrophysical origins of compact binaries. Yet it remains absent from routine LIGO-Virgo-KAGRA analyses, in part because of the prohibitive computational cost of generating eccentric template waveforms. The complicated morphology of these waveforms due to the eccentric orbital timescale variations makes it difficult to construct their accurate and efficient surrogate models, especially for waveforms long enough to comprehensively cover the sensitivity bands of current ground-based gravitational-wave detectors. We present a novel and scalable surrogate building technique which makes surrogate modeling of long-duration eccentric binary black hole waveforms both feasible and highly efficient. The technique aims to simplify the harmonic content of intermediate eccentric waveform data-pieces by modeling them in terms of an angular orbital element called the mean anomaly, instead of time. We show that this parameterization yields much more compressed surrogates than the standard time-based parameterizations. We also significantly simplify variations in waveform data-pieces across the parameter space by expressing them in terms of the instantaneous orbital eccentricity and mean anomaly to ease their parametric fitting. Building on these developments, we construct InspiralESIGMASur: a $2.77 \times 10^6M$ (850-1250 orbits) long non-spinning surrogate for the inspiral-only eccentric waveform model InspiralESIGMA [K. Paul et al., Phys. Rev. D 111, 084074 (2025)]. The methods presented in this work make it feasible to build long-duration eccentric surrogates for current as well as future third-generation gravitational-wave detectors.

gr-qc

Laying the foundation of the effective-one-body waveform models SEOBNRv5: improved accuracy and efficiency for spinning non-precessing binary black holes

We present SEOBNRv5HM, a more accurate and faster inspiral-merger-ringdown gravitational waveform model for quasi-circular, spinning, nonprecessing binary black holes within the effective-one-body (EOB) formalism. Compared to its predecessor, SEOBNRv4HM, the waveform model i) incorporates recent high-order post- Newtonian results in the inspiral, with improved resummations, ii) includes the gravitational modes (l, |m|) = (3, 2), (4, 3), in addition to the (2, 2), (3, 3), (2, 1), (4, 4), (5, 5) modes already implemented in SEOBNRv4HM, iii) is calibrated to larger mass-ratios and spins using a catalog of 442 numerical-relativity (NR) simulations and 13 additional waveforms from black-hole perturbation theory, iv) incorporates information from second-order gravitational self-force (2GSF) in the nonspinning modes and radiation-reaction force. Computing the unfaithfulness against NR simulations, we find that for the dominant (2, 2) mode the maximum unfaithfulness in the total mass range $10-300 M_{\odot}$ is below $10^{-3}$ for 90% of the cases (38% for SEOBNRv4HM). When including all modes up to l = 5 we find 98% (49%) of the cases with unfaithfulness below $10^{-2} (10^{-3})$, while these numbers reduce to 88% (5%) when using SEOBNRv4HM. Furthermore, the model shows improved agreement with NR in other dynamical quantities (e.g., the angular momentum flux and binding energy), providing a powerful check of its physical robustness. We implemented the waveform model in a high-performance Python package (pySEOBNR), which leads to evaluation times faster than SEOBNRv4HM by a factor 10 to 50, depending on the configuration, and provides the flexibility to easily include spin-precession and eccentric effects, thus making it the starting point for a new generation of EOBNR waveform models (SEOBNRv5) to be employed for upcoming observing runs of the LIGO-Virgo-KAGRA detectors.

gr-qc

Accurate waveforms for generic planar-orbit binary black holes: The multipolar effective-one-body model SEOBNRv6EHM

Accurate and computationally efficient waveform models are required to infer the parameters of compact binaries from their gravitational wave (GW) emission. Among these parameters, orbital eccentricity serves as a smoking gun for dynamical formation channels and must be accounted for to avoid systematic errors in GW analyses. Here, we present SEOBNRv6EHM, a time-domain, multipolar waveform model for binaries on generic planar orbits, calibrated to quasi-circular (QC) numerical-relativity (NR) simulations from the SXS collaboration. In addition to the dominant $(2,2)$ mode, the model provides the $(2,1)$, $(3,3)$, $(3,2)$, $(4,4)$, and $(4,3)$ multipoles for the full inspiral-merger-ringdown process of coalescing binaries, as well as for dynamical captures and scattering encounters. The model is built within the effective-one-body (EOB) framework, and it employs novel resummations of the radiation-reaction force and waveform modes. We validate its accuracy through comparisons against 592 QC, 319 eccentric, one dynamical-capture, and two scattering SXS NR waveforms, and through scattering-angle comparisons against 61 SXS NR simulations. For QC and small-eccentricity binaries, its accuracy is comparable to previous-generation SEOBNRv5 models. For highly eccentric systems, however, SEOBNRv6EHM attains unprecedented accuracy, with waveform mismatches remaining below or close to $ 2\% $ across the total mass range $ 20-200\, \mathrm{M}_\odot $ for eccentricities up to $\sim 0.9$ at 14 periastron passages before merger. Additionally, SEOBNRv6EHM achieves waveform-generation walltimes that are $ 2 - 6 $ times faster than other state-of-the-art EOB eccentric models, enabling efficient and accurate applications in GW astronomy.

gr-qc

Assessing the Relative Importance of Neutrino Matter Interaction Channels in Post-Merger Remnant of Binary Neutron Stars

Neutron star mergers are amongst the most promising sources for the joint detection of gravitational waves and electromagnetic signals. They are also potential sites for the production of r-process elements and probes of the equation of state of matter above nuclear saturation density. Neutrino-matter interactions during and after merger strongly influence the thermodynamic evolution and composition of the remnant and its outflows, thereby affecting kilonova emission and nucleosynthesis yields. However, existing merger simulations remain limited by significant approximations in the treatment of neutrino transport and interaction rates. In this work, we assess the thermodynamic conditions under which neutrinos decouple from matter and show the effect of charged-current absorption, quasi-elastic scattering on nucleons and nuclei, pair-production processes, and inelastic neutrino-electron scattering for electron neutrinos, electron antineutrinos, and heavy-lepton neutrinos in the different thermodynamical conditions sampled by a simulation using an energy-dependent Monte Carlo neutrino transport. We first estimate opacities in the post-merger remnant assuming neutrinos in equilibria with the fluid, and find results consistent with previous studies performed on simulations using a gray two-moment scheme. We note the very distinct regions in which nucleon-nucleon Bremmstrahlung and electron-positron annihilation are active (high and low density regions, respectively). We then evaluate opacities using the actual distribution function of neutrinos within a Monte Carlo simulation. We show greatly increased pair annihilation rates in cold, low-density regions, especially for heavy-lepton neutrinos. We also show that inelastic scattering on electrons, which has not been included in merger simulations so far, makes important contributions to the thermalization of heavy-lepton neutrinos.

astro-ph.HE

Merger remnant and eccentricity dynamics surrogates for eccentric nonspinning black hole binaries

Accurate models of merger remnants are increasingly important for gravitational-wave science, including precision tests of gravity with ringdown, inference of black-hole populations, and modeling hierarchical mergers. For eccentric binaries, remnant mass, spin, and recoil carry nontrivial imprints of eccentricity that are both physically informative and more challenging to model, yet remain less developed than in the quasi-circular case. We present two new models trained on numerical-relativity (NR) simulations of unequal-mass, non-spinning eccentric binary black holes: NRSurE_q4NoSpin_Remnant, which predicts remnant properties, and NRSurE_q4NoSpin_Dynamics, a time-domain surrogate for the evolution of eccentricity and mean anomaly. Both models are trained on NR simulations over a three-dimensional parameter space with mass ratios $q \leq 4$, eccentricity $e < 0.23$, and mean anomaly $\ell \in [0,2π)$ radians, where both $e$ and $\ell$ defined at $t=-1000M$ relative to peak amplitude and $M$ is the total mass. We highlight some applications, including the phenomenological impact of eccentricity on remnant properties and the enhancement or suppression of recoil. We also provide error estimates for all modeled quantities, supporting reliable use in current and future gravitational-wave parameter-estimation analyses. Both models will be made available through open-source codes.

gr-qc

Biased parameter inference of eccentric, spin-precessing binary black holes

While the majority of gravitational wave (GW) events observed by the LIGO and Virgo detectors are consistent with mergers of binary black holes (BBHs) on quasi-circular orbits, some events are also consistent with non-zero orbital eccentricity, indicating that the binaries could have formed via dynamical interactions. Moreover, there may be GW events which show support for spin-precession, eccentricity, or both. In this work, we study the interplay of spins and eccentricity on the parameter estimation of GW signals from BBH mergers. We inject eccentric signals with no spins, aligned spins, and precessing spins using hybrids, TEOBResumS-DALI, and new Numerical Relativity (NR) simulations, respectively, and study the biases in the posteriors of source parameters when these signals are recovered with a quasi-circular precessing-spin waveform model, as opposed to an aligned-spin eccentric waveform model. We find significant biases in the source parameters, such as chirp mass and spin-precession ($χ_p$), when signals from highly-eccentric BBHs are recovered with a quasi-circular waveform model. Moreover, we find that for signals with both eccentricity and spin-precession effects, Bayes factor calculations confirm that an eccentric, aligned-spin model is preferred over a quasi-circular precessing-spin model. Our study highlights the complex nature of GW signals from eccentric, precessing-spin binaries and the need for readily usable inspiral-merger-ringdown eccentric, spin-precessing waveform models for unbiased parameter estimation.

gr-qc

Waveform Modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.

gr-qc

Including higher-order modes in a quadrupolar eccentric numerical relativity surrogate using universal eccentric modulation functions

\texttt{gwNRHME} is a framework that converts multi-modal (i.e., containing several spherical harmonic modes) quasi-circular waveforms into their eccentric counterparts, provided the quadrupolar eccentric mode is known, by exploiting universal eccentric modulation functions. Leveraging this framework, we combine the quasi-circular NR surrogate model \texttt{NRHybSur3dq8} with the quadrupolar, non-spinning, eccentric surrogate \texttt{NRSurE\_q4NoSpin\_22} to construct a multi-modal, non-spinning, eccentric model, denoted as \model{}, which includes nine modes: $(2,\{1,2\})$, $(3,\{1,2,3\})$, $(4,\{2,3,4\})$, and $(5,5)$. When compared against 156 eccentric SXS NR waveforms, \model{} achieves median frequency-domain mismatches (computed using the Advanced LIGO design sensitivity) of $\sim 9\times 10^{-5}$, with a standard deviation of $\sim 2 \times 10^{-4}$. To demonstrate the modularity of the framework, we further combine \texttt{NRSurE\_q4NoSpin\_22} with effective-one-body (EOB) models \texttt{SEOBNRv5HM} and \texttt{TEOBResumS-Dali} in their non-spinning limits, yielding eccentric waveforms with median mismatches of $\sim 2\times10^{-4}$ and $\sim 10^{-3}$, respectively, with standard deviation of $\sim 2 \times 10^{-3}$ and $\sim 2 \times 10^{-2}$ respectively. Finally, we provide both a surrogate model, \texttt{gwEccEvolve\_q4NoSpin\_Sur}, and an analytical model, \texttt{gwEccEvNSv2}, for the eccentricity evolution up to $2M$ before merger, based on eccentricity definitions derived from the universal modulation functions. The \texttt{gwNRHME} framework is publicly available through the \texttt{gwModels} package, and the resulting waveform models will be released via the \texttt{gwsurrogate} package.

gr-qc

Emergent Turbulence in Nonlinear Gravity

Gravity in nonlinear and dynamical regimes underpins spectacular astrophysical phenomena and observable consequences, from the early universe to black hole collisions. In these extreme environments, inverse energy cascades - mediated by nonlinear interactions - may help explain the near scale-invariance of cosmic structure and the simplicity of gravitational waves from binary black hole mergers. Yet the presence, characteristics, and generality of such interactions in full General Relativity remain largely unexplored. Here we show that two types of nonlinear interactions - a four-mode and a three-mode interaction - emerge in the fully nonlinear regime, and can indeed channel inverse energy cascades by inducing resonant and anti-damping instabilities. This establishes what was previously only hinted at in highly specialized perturbative contexts. We further demonstrate a ``laminar'' to ``turbulent'' transition for the largest-possible angular structure in General Relativity, whereas finer structures remain persistently turbulent. Our results reveal the impact and generality of these nonlinear interactions (instabilities), which can be key to understanding observations ranging from cosmological to kilometer scales. We anticipate that our work will shed new light on nonlinear gravitational phenomena and their consequences, such as constructing gravitational wave templates and testing General Relativity in the most extreme regime. Moreover, our work is a starting point for addressing nonlinear gravitational interactions using ideas and methods inspired by fluid dynamics.

gr-qc

Black-hole scattering with numerical relativity: Self-force extraction and post-Minkowskian validation

The asymptotic nature of unbound binary-black-hole encounters provides a clean method for comparing different approaches for modeling the two-body problem in general relativity. In this work, we use numerical relativity simulations of black-hole scattering, generated using the Spectral Einstein Code, to explore the self-force and post-Minkowskian expansions of the scattering angle. First, we use a set of unequal-mass simulations to extract the self-force contributions to the scattering angle. Our main result is that using information up to second-order in the symmetric mass ratio (2SF) reproduces numerical relativity within the error bars across the full range of mass-ratios, including equal mass. Next, we compare our numerical relativity results to state-of-the-art post-Minkowskian predictions at larger impact parameters than previously explored. We find good agreement in the weak-field regime and discuss the relative importance of higher-order terms.

gr-qc

Highly accurate simulations of asymmetric black-hole scattering and cross validation of effective-one-body models

The study of unbound binary-black-hole encounters provides a gauge-invariant approach to exploring strong-field gravitational interactions in two-body systems, which can subsequently inform waveform models for bound orbits. In this work, we present 60 new highly accurate numerical relativity (NR) simulations of black-hole scattering, generated using the Spectral Einstein Code (SpEC). Our simulations include 14 spin-aligned configurations, as well as 16 configurations with unequal masses, up to a mass ratio of 10. We perform the first direct comparison of scattering angles computed using different NR codes, finding good agreement. We compare our NR scattering angle results to the post-Minkowskian (PM)-based effective-one-body (EOB) closed-form models SEOB-PM and $w_{\rm EOB}$, finding less than 5% deviation except near the scatter-capture separatrix. Comparisons with the post-Newtonian-based EOB evolution models SEOBNRv5 and TEOBResumS-Dalí reveal that the former agrees within 8% accuracy with non-spinning NR results across most parameter ranges, whereas the latter matches similarly at lower energies but diverges significantly at higher energies. Both evolution EOB models exhibit increased deviations for spinning systems, predicting a notably different location of the capture separatrix compared to NR. Our key result is the first measurement of disparate scattering angles from NR simulations due to asymmetric gravitational-wave emission. We compare these results to SEOB-PM models constructed to calculate the scattering angle of a single black hole in asymmetric systems.

gr-qc

Systematic Biases in Estimating the Properties of Black Holes Due to Inaccurate Gravitational-Wave Models

Gravitational-wave (GW) observations of binary black-hole (BBH) coalescences are expected to address outstanding questions in astrophysics, cosmology, and fundamental physics. Realizing the full discovery potential of upcoming LIGO-Virgo-KAGRA (LVK) observing runs and new ground-based facilities hinges on accurate waveform models. Using linear-signal approximation methods and Bayesian analysis, we start to assess our readiness for what lies ahead using two state-of-the-art quasi-circular, spin-precessing models: \texttt{SEOBNRv5PHM} and \texttt{IMRPhenomXPHM}. We ascertain that current waveforms can accurately recover the distribution of masses in the LVK astrophysical population, but not spins. We find that systematic biases increase with detector-frame total mass, binary asymmetry, and spin-precession, with most such binaries incurring parameter biases, extending up to redshifts $\sim3$ in future detectors. Furthermore, we examine three ``golden'' events characterized by large mass ratios, significant spin magnitudes, and high precession, evaluating how systematic biases may affect their scientific outcomes. Our findings reveal that current waveforms fail to enable the unbiased measurement of the Hubble-Lemaître parameter from loud signals, even for current detectors. Moreover, highly asymmetric systems within the lower BH mass-gap exhibit biased measurements of the secondary-companion mass, which impacts the physics of both neutron stars and formation channels. Similarly, we deduce that the primary mass of massive binaries ($ > 60 M_\odot$) will also be biased, affecting supernova physics. Future progress in analytical calculations and numerical-relativity simulations, crucial for calibrating the models, must target regions of the parameter space with significant biases to develop more accurate models. Only then can precision GW astronomy fulfill the promise it holds.

gr-qc

Ringdown spectroscopy of phenomenologically modified black holes

The characteristic oscillations of black holes, as described by their quasinormal mode (QNM) spectrum, play a fundamental role in testing general relativity with gravitational waves. The so-called parametrized QNM framework was introduced to predict perturbative changes in the spectrum due to small deviations from general relativity. In this work, we extend the framework to model time domain signals and study the excitation of quasinormal modes from the time evolution of initial data. Specifically, we quantify whether the perturbative eigenvalue predictions agree with extracting excited quasinormal modes from such simulations. Addressing this issue is particularly important in the context of agnostic ringdown tests and the possible presence of spectral instabilities, which may diminish the promises of black hole spectroscopy. We find that the extracted quasinormal modes agree well with the perturbative predictions, underlining that these types of modifications can, in principle, be robustly tested from real observations. Moreover, we also report the importance of including late-time tails for accurate mode extractions. Finally, we provide a WKB-inspired analysis supporting the importance of the peak of the scattering potential and show robust scaling relations.

gr-qc

Eccentric binary black holes: A new framework for numerical relativity waveform surrogates

Mounting evidence indicates that some of the gravitational wave signals observed by the LIGO/Virgo/KAGRA observatories might arise from eccentric compact object binaries, increasing the urgency for accurate waveform models for such systems. While for non-eccentric binaries, surrogate models are efficient and accurate, the additional features due to eccentricity have posed a challenge. In this letter, we present a novel method for decomposing eccentric numerical relativity waveforms which makes them amenable to surrogate modelling techniques. We parameterize the inspiral in the radial phase domain, factoring out eccentricity-induced dephasing and thus enhancing compressibility and accuracy. This is combined with a second surrogate for the merger-ringdown in the time-domain and a novel technique to take advantage of the approximate periodicity with radial oscillations during the inspiral. We apply this procedure to the $(2,2)$ mode for non-spinning black hole binaries, and demonstrate that the resulting surrogate, NRSurE_q4NoSpin_22, is able to faithfully reproduce the underlying numerical relativity waveforms, with maximum mismatches of $5\times10^{-4}$ and median mismatches of $2\times10^{-5}$. This technique paves the way for high-accuracy parameter estimation with eccentric models, a key ingredient for astrophysical inference and tests of general relativity.

gr-qc

Defining eccentricity for spin-precessing binaries

Standardizing the definition of eccentricity is necessary for unambiguous inference of the orbital eccentricity of compact binaries from gravitational wave observations. In previous works, we proposed a definition of eccentricity for systems without spin-precession that relies solely on the gravitational waveform, is applicable to any waveform model, and has the correct Newtonian limit. In this work, we extend this definition to spin-precessing systems. This simple yet effective extension relies on first transforming the waveform from the inertial frame to the coprecessing frame, and then adopting an amplitude and a phase with reduced spin-induced effects. Our method includes a robust procedure for filtering out spin-induced modulations, which become non-negligible in the small eccentricity and large spin-precession regime. Finally, we apply our method to a set of Numerical Relativity and Effective One Body waveforms to showcase its robustness for generic eccentric spin-precessing binaries. We make our method public via Python implementation in \texttt{gw\_eccentricity}.

gr-qc