The Inspiral Merger Ringdown Consistency Test (IMRCT) is one among a battery of tests of general relativity (GR) employed by the LIGO-Virgo-KAGRA (LVK) collaboration. It is used to search for deviations from GR in detected gravitational waves (GWs) from compact binary coalescences (CBCs) in a model-agnostic way. The test compares source parameter estimates extracted independently from the inspiral and post-inspiral portions of the CBC signals and, therefore, crucially relies on the accurate modeling of the waveform. Current implementations of the IMRCT routinely use quasicircular waveforms, under the assumption that the residual eccentricity of the binary when the emitted GWs enter the frequency band of the LVK detector network will be negligible. In this work, we perform a detailed study to investigate the typical magnitudes of this residual eccentricity that could potentially lead to spurious violations of the IMRCT. To that end, we conduct injection campaigns for a range of eccentricities and recover with both quasicircular and eccentric waveforms. We find that an eccentric GW signal from a GW150914-like system with eccentricity $e_{\text{gw}} \gtrsim$ 0.04 at an orbit averaged frequency $\langle f_{\text{ref}} \rangle=$ 25 Hz breaks the IMRCT if recovered with quasicircular waveforms at $\gtrsim 68%$ confidence. The violation becomes more severe ($\gtrsim 90%$ confidence) for $e_{\text{gw}} =$ 0.055 at $\langle f_{\text{ref}} \rangle=$ 25 Hz. On the other hand, when eccentric waveforms are used, the IMRCT remains intact for all eccentricities considered. We also briefly investigate the effect of the magnitude and orientation (aligned/antialigned) of the component spins of the binary on the extent of the spurious violations of the IMRCT. Our work, therefore, demonstrates the need for accurate eccentric waveform models in the context of tests of GR.

**A study of the inspiral-merger-ringdown consistency test with
gravitational-wave signals from compact binaries in eccentric orbits**

__Md Arif Shaikh__, S. A. Bhat and S. J. Kapadia

Phys. Rev. D,
**110**, 024030, (2024).

The Inspiral Merger Ringdown Consistency Test (IMRCT) is one among a battery of tests of general relativity (GR) employed by the LIGO-Virgo-KAGRA (LVK) collaboration. It is used to search for deviations from GR in detected gravitational waves (GWs) from compact binary coalescences (CBCs) in a model-agnostic way. The test compares source parameter estimates extracted independently from the inspiral and post-inspiral portions of the CBC signals and, therefore, crucially relies on the accurate modeling of the waveform. Current implementations of the IMRCT routinely use quasicircular waveforms, under the assumption that the residual eccentricity of the binary when the emitted GWs enter the frequency band of the LVK detector network will be negligible. In this work, we perform a detailed study to investigate the typical magnitudes of this residual eccentricity that could potentially lead to spurious violations of the IMRCT. To that end, we conduct injection campaigns for a range of eccentricities and recover with both quasicircular and eccentric waveforms. We find that an eccentric GW signal from a GW150914-like system with $e_{\text{gw}} \gtrsim$ 0.04 at an orbit averaged frequency $\langle f_{\text{ref}} \rangle=$ 25 Hz breaks the IMRCT if recovered with quasicircular waveforms at $\gtrsim 68%$ confidence. The violation becomes more severe ($\gtrsim 90%$ confidence) for $e_{\text{gw}} =$ 0.055 at $\langle f_{\text{ref}} \rangle=$ 25 Hz. On the other hand, when eccentric waveforms are used, the IMRCT remains intact for all eccentricities considered. We also briefly investigate the effect of the magnitude and orientation (aligned/antialigned) of the component spins of the binary on the extent of the spurious violations of the IMRCT. Our work, therefore, demonstrates the need for accurate eccentric waveform models in the context of tests of GR.

**A study of the Inspiral-Merger-Ringdown Consistency Test with
gravitational-wave signals from compact binaries in eccentric orbits**

__Md Arif Shaikh__, Sajad A. Bhat and Shasvath J. Kapadia

**arXiv:2402.15110**, (2022)

Eccentric compact binary mergers are significant scientific targets for current and future gravitational wave observatories. To detect and analyze eccentric signals, there is an increasing effort to develop waveform models, numerical relativity simulations, and parameter estimation frameworks for eccentric binaries. Unfortunately, current models and simulations use different internal parametrizations of eccentricity in the absence of a unique natural definition of eccentricity in general relativity, which can result in incompatible eccentricity measurements. In this paper, we adopt a standardized definition of eccentricity and mean anomaly based solely on waveform quantities and make our implementation publicly available through an easy-to-use python package, gw_eccentricity. This definition is free of gauge ambiguities, has the correct Newtonian limit, and can be applied as a postprocessing step when comparing eccentricity measurements from different models. This standardization puts all models and simulations on the same footing and enables direct comparisons between eccentricity estimates from gravitational wave observations and astrophysical predictions. We demonstrate the applicability of this definition and the robustness of our implementation for waveforms of different origins, including post-Newtonian theory, effective-one-body, extreme mass ratio inspirals, and numerical relativity simulations. We focus on binaries without spin precession in this work, but possible generalizations to spin-precessing binaries are discussed.

**Defining eccentricity for gravitational wave astronomy**

__Md Arif
Shaikh__, Vijay Varma, Harald P. Pfeiffer, Antoni Ramos-Buades, and Maarten
van de Meent

Phys. Rev. D,
**108**, 104007, (2023).

First and foremost, I would like to express my heartfelt gratitude to Prof. Hyung Mok Lee for his exceptional kindness and generosity throughout my stay. I had numerous opportunities to collaborate with groups and participate in meetings all around the world.

I also want to extend my thanks to all my colleagues in the gravitational wave group at SNU and at the Center for the GW Universe. It has been a wonderful journey living in Korea, and I hope to return in the near future as a visitor. Thank you for making my time at SNU so memorable.

]]>This marks my second attendance at the KAS meeting, and it's particularly exciting to have the event hosted in the beautiful location of Jeju. I'm eagerly anticipating reconnecting with familiar faces from the Korean Astronomical Society.

Jeju, situated in the southern region of Korea, is a renowned tourist destination known for its captivating beauty. Amid the conference, I'm hoping to set aside some time to explore the island's attractions before heading back to Seoul.

]]>Travelling in Korea is very easy. I took the KTX train from Seoul to SinGyeongju. It took about two hours. From SinGyeongju station there are frequent buses to the Gyeongju city which takes less than half an hour. However, since the conference was at the Kolon Hotel, which is a little far and located near the southeastern part of Gyeongju, I just took a cab. Gyeongju is very close to Busan and can be reached by either KTX or bus very easily.

**Bulguksa temple:**Very close to Kolon Hotel and reachable by Bus No 10 or 11 from the city. It is said to be one of the most sacred Buddhist temples in Korea. There are a lot of places to eat here. Cafes and convenience stores are there if you need something.**Seokguram Grotto:**A UNESCO World Heritage. From the Bulguksa temple bust, there is Bus No 12 which goes to this place every one hour so and returns also every one hour.**Gyeongju National Museum:**Located near the city itself. A Museum with articles from the Silla period. Free to enter.**Woljeonggyo Bridge:**Enjoyed a nice walk from the National Museum to the Woljeonggyo Bridge through the Korean rural landscape. From afar the bridge looks beautiful.**Gyeongju Daereungwon Ancient Tomb Complex:**Enjoyed a walk through the tomb complex. Many tombs of the Silla kings.**Golgulsa Temple:**From the city, took the Bus No 150 to Andong, the entrance of the Golgulsa temple. From Andong, it is a 20 minutes walk.**Najeong Beach:**Took Bus 150 again from Andong to reach the Najeong beach on the east coast of Korea. It took only 10 minutes from Andong.

Today Prof David Shoemaker joined our group in an exciting discussion on the future gravitational wave detectors - including LISA, Cosmic Explorer and Einstein Telescope. We got many interesting insights on the Advanced LIGO project as well as an idea of the challenges that lies ahead in the future gravitational detectors.

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