Falsifications and constraints due to GW measurements

[Auto-Didact]

This thread is to serve as
- a collection of theories that have been falsified by and/or have had new constrained placed on them by the ongoing gravitational wave measurements.
- a place to discuss the further constraining/falsifying of still existing models using GW data.

I'll start by posting a few papers offering falsifications and/or new constraints:
Boran et al. 2017, GW170817 Falsifies Dark Matter Emulators

On August 17, 2017 the LIGO interferometers detected the gravitational wave (GW) signal (GW170817) from the coalescence of binary neutron stars. This signal was also simultaneously seen throughout the electromagnetic (EM) spectrum from radio waves to gamma-rays. We point out that this simultaneous detection of GW and EM signals rules out a class of modified gravity theories, which dispense with the need for dark matter. This simultaneous observation also provides the first ever test of Einstein's Weak Equivalence Principle (WEP) between gravitons and photons. We calculate the Shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation in arXiv:1710.05834) to be about 1000 days. Using this estimate for the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma-rays, we can constrain violations of WEP using the parameterized post-Newtonian (PPN) parameter γ, and is given by |γGW−γEM|<3.9×10−8.

Baker et al. 2017, Strong constraints on cosmological gravity from GW170817 and GRB 170817A

The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational wave signal (GW170817) from the merger of two neutron stars opens a completely new arena for testing theories of gravity. We show that this measurement allows us to place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing us to place an independent bound on the graviton mass in bimetric theories of gravity. These constraints severely reduce the viable range of cosmological models that have been proposed as alternatives to general relativistic cosmology.

Di Valentino et al. 2017, Cosmological constraints combining Planck with the recent gravitational-wave standard siren measurement of the Hubble constant

The recent observations of gravitational-wave and electromagnetic emission produced by the merger of the binary neutron-star system GW170817 have opened the possibility of using standard siren to constrain the value of the Hubble constant. While the reported bound is significantly weaker than those recently derived by usual luminosity distances methods, they do not require any form of cosmic distance ladder and can be considered as complementary and, in principle, more conservative. Here we combine the new measurement with the Planck Cosmic Microwave Background observations in a 12 parameters extended LambdaCDM scenario, where the Hubble constant is weakly constrained by CMB data and bound to a low value H0=55+7−20 km/s/Mpc at 68 % C.L. The non-Gaussian shape of the GW170817 bound makes lower values of the Hubble constant in worst agreement with observations. The inclusion of the new GW170817 Hubble constant measurement significantly reduces the allowed parameter space, improving the cosmological bounds on several parameters as the neutrino mass, curvature and the dark energy equation of state.

Margalit et al. 2017, Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817

We combine electromagnetic (EM) and gravitational wave (GW) information on the binary neutron star (NS) merger GW170817 in order to constrain the radii Rns and maximum mass Mmax of NSs. GW170817 was followed by a range of EM counterparts, including a weak gamma-ray burst (GRB), kilonova (KN) emission from the radioactive decay of the merger ejecta, and X-ray/radio emission consistent with being the synchrotron afterglow of a more powerful off-axis jet. The type of compact remnant produced in the immediate merger aftermath, and its predicted EM signal, depend sensitively on the high-density NS equation of state (EOS). For a soft EOS which supports a low Mmax, the merger undergoes a prompt collapse accompanied by a small quantity of shock-heated or disk wind ejecta, inconsistent with the large quantity ≳10−2M⊙ of lanthanide-free ejecta inferred from the KN. On the other hand, if Mmax is sufficiently large, then the merger product is a rapidly-rotating supramassive NS (SMNS), which must spin-down before collapsing into a black hole. A fraction of the enormous rotational energy necessarily released by the SMNS during this process is transferred to the ejecta, either into the GRB jet (energy EGRB) or the KN ejecta (energy Eej), also inconsistent with observations. By combining the total binary mass of GW170817 inferred from the GW signal with conservative upper limits on EGRB and Eej from EM observations, we constrain the likelihood probability of a wide-range of previously-allowed EOS. These two constraints delineate an allowed region of the Mmax−Rns parameter space, which once marginalized over NS radius places an upper limit of Mmax≲2.17M⊙ (90\%), which is tighter or arguably less model-dependent than other current constraints.

Ezquiaga et al. 2017, Dark Energy after GW170817 (1)

Multi-messenger gravitational wave (GW) astronomy has commenced with the detection of the binary neutron star merger GW170817 and its associated electromagnetic counterparts. The almost coincident observation of the GW and the gamma ray burst GRB170817A constrain the speed of GWs at the level of |cg/c−1|≤4.5⋅10−16. We use this result to probe the nature of dark energy (DE), showing that scalar-tensor theories with derivative interactions with the curvature are highly disfavored. As an example we consider the case of Galileons, a well motivated gravity theory with viable cosmology, which predicts a variable GW speed at low redshift, and is hence strongly ruled out by GW170817. Our result essentially eliminates any cosmological application of these DE models and, in general, of quartic and quintic Horndeski and most beyond Horndeski theories. We identify the surviving scalar-tensor models and, in particular, present specific beyond Horndeski theories avoiding this constraint. The viable scenarios are either conformally equivalent to theories in which cg=c or rely on cancellations of the anomalous GW speed that are valid on arbitrary backgrounds. Our conclusions can be extended to any other gravity theory predicting an anomalous GW propagation speed such as Einstein-Aether, Ho\v{r}ava gravity, Generalized Proca, TeVeS and other MOND-like gravities.

Sakstein et al. 2017, Implications of the Neutron Star Merger GW170817 for Cosmological Scalar-Tensor Theories

The LIGO/VIRGO collaboration has recently announced the detection of gravitational waves from a neutron star-neutron star merger (GW170817) and the simultaneous measurement of an optical counterpart (the gamma-ray burst GRB 170817A). The close arrival time of the gravitational and electromagnetic waves limits the difference in speed of photons and gravitons to be less than about one part in 1015. This has three important implications for cosmological scalar-tensor gravity theories that are often touted as dark energy candidates and alternatives to ΛCDM. First, for the most general scalar-tensor theories---beyond Horndeski models---three of the five parameters appearing in the effective theory of dark energy can now be severely constrained on astrophysical scales; we present the results of combining the new gravity wave results with galaxy cluster observations. Second, the combination with the lack of strong equivalence principle violations exhibited by the supermassive black hole in M87, constrains the quartic galileon model to be cosmologically irrelevant. Finally, we derive a new bound on the disformal coupling to photons that implies that such couplings are irrelevant for the cosmic evolution of the field.

Creminelli at al. 2017, Dark Energy after GW170817 (2)

The observation of GW170817 and its electromagnatic counterpart implies that gravitational waves travel at the speed of light, with deviations smaller than a few parts in 10−15. We discuss the consequences of this experimental result for models of dark energy and modified gravity characterized by a single scalar degree of freedom. To avoid tuning, the speed of gravitational waves must be unaffected not only for our particular cosmological solution, but also for nearby solutions obtained by slightly changing the matter abundance. For this to happen the coefficients of various operators must satisfy precise relations that we discuss both in the language of the Effective Field Theory of Dark Energy and in the covariant one, for Horndeski, beyond Horndeski and degenerate higher-order theories. The simplification is dramatic: of the three functions describing quartic and quintic beyond Horndeski theories, only one remains and reduces to a standard conformal coupling to the Ricci scalar for Horndeski theories. We show that the deduced relations among operators do not introduce further tuning of the models, since they are stable under quantum corrections.

Wang et al. 2017, GW170817/GRB 170817A/AT2017gfo association: some implications for physics and astrophysics

On 17 August 2017, a gravitational wave event (GW170817) and an associated short gamma-ray burst (GRB 170817A) from a binary neutron star merger had been detected. The followup optical/infrared observations also identified the macronova/kilonova emission (AT2017gfo). In this work we discuss some implications of the remarkable GW170817/GRB 170817A/AT2017gfo association. We show that the ∼1.7s time delay between the gravitational wave (GW) and GRB signals imposes very tight constraint on the superluminal movement of gravitational waves (i.e., the relative departure of GW velocity from the speed of light is ≤4.3×10−16) or the possible violation of weak equivalence principle (i.e., the difference of the gamma-ray and GW trajectories in the gravitational field of the galaxy and the local universe should be within a factor of ∼3.4×10−9). The so-called Dark Matter Emulators and a class of contender models for cosmic acceleration ("Covariant Galileon") are ruled out, too. The successful identification of Lanthanide elements in the macronova/kilonova spectrum also excludes the possibility that the progenitors of GRB 170817A are a binary strange star system. The high neutron star merger rate (inferred from both the local sGRB data and the gravitational wave data) together with the significant ejected mass strongly suggest that such mergers are the prime sites of heavy r-process nucleosynthesis.

 

[mfb]

A nice collection.

I wonder how constraints on GR alternatives will change with future observations. Improving the time correlation between GW and electromagnetic signal by a small factor shouldn't make a big difference. We can get more independent estimates of the Hubble constant, of course, but that is a different topic.

 

[lpetrich]

If one could observe more of this sort of event, one could get some idea of the time from the G-wave signal to the gamma-ray one. One may then look for how it varies with distance, or more precisely, estimated Shapiro gravitational time delay from nearby galaxies. The error in the time-delay estimate will go as 1/sqrt(N) for N events, meaning that it may take a lot of events to improve very much on this result.

Also, it's an interesting term for G-wave events: "standard siren". Presumably because "standard candle" is not a good fit.

 

[physika]

General Relativity rules!


Reining in Alternative Gravity

https://physics.aps.org/articles/v10/134#c5

----

Dark Energy After GW170817: Dead Ends and the Road Ahead

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.251304

We use this result to probe the nature of dark energy (DE), showing that a large class of scalar-tensor theories and DE models are highly disfavored. As an example we consider the covariant Galileon, a cosmologically viable, well motivated gravity theory which predicts a variable GW speed at low redshift. Our results eliminate any late-universe application of these models, as well as their Horndeski and most of their beyond Horndeski generalizations. Three alternatives (and their combinations) emerge as the only possible scalar-tensor DE models: (1) restricting Horndeski’s action to its simplest terms, (2) applying a conformal transformation which preserves the causal structure, and (3) compensating the different terms that modify the GW speed (to be robust, the compensation has to be independent on the background on which GWs propagate). Our conclusions extend to any other gravity theory predicting varying cg such as Einstein-Aether, Hořava gravity, Generalized Proca, tensor-vector-scalar gravity (TEVES), and other MOND-like gravities.


.

 

[strangerep]

ArXiv version here.

 

[Chronos]

I am inclined to interpret all these as merely slightly different ways of reaching the same core conclusion: empty 'space' has no measurable affect upon the propagation speed of gravitational or electromagnetic waves. Sounds suspiciously similar to the conclusion reached by Einstein.

 

[physika]

.

Bounding the Speed of Gravity with Gravitational Wave Observations
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.161102

The time delay between gravitational wave signals arriving at widely separated detectors can be used to place upper and lower bounds on the speed of gravitational wave propagation. Using a Bayesian approach that combines the first three gravitational wave detections reported by the LIGO Scientific and Virgo Collaborations we constrain the gravitational waves propagation speed cgw to the 90% credible interval 0.55c<cgw<1.42c, where c is the speed of light in vacuum. These bounds will improve as more detections are made and as more detectors join the worldwide network. Of order 20 detections by the two LIGO detectors will constrain the speed of gravity to within 20% of the speed of light, while just five detections by the LIGO-Virgo-Kagra network will constrain the speed of gravity to within 1% of the speed of light.

.

 

[ohwilleke]

Not sure if this is on topic or not, although it is certainly related to some extent.

Indications of an unexpected signal associated with the GW170817 binary neutron star inspiral
E. Fischbach, V. E. Barnes, N. Cinko, J. Heim, H. B. Kaplan, D. E. Krause, J. R. Leeman, S. A. Mathews, M. J. Mueterthies, D. Neff, M. Pattermann
(Submitted on 10 Jan 2018)
We report experimental evidence at the 2.5σ level for an unexpected signal associated with the GW170817 binary neutron star inspiral. This evidence derives from a laboratory experiment simultaneously measuring the β-decay rates of Si-32 and Cl-36 in a common detector. Whereas the Si-32 and Cl-36 decay rates show no statistical correlation before or after the inspiral, they are highly correlated (∼95%) in the 5 hour time interval immediately following the inspiral. If we interpret this correlation as arising from the influence of particles emitted during the inspiral, then we can estimate the mass mx of these particles from the time delay between the gravity-wave signal and a peak in the β-decay data. We find for particles of energy 10 MeV, mx ≲ 16 eV which includes the neutrino mass region mν ≲ 2 eV. The latter is based on existing limits for the masses mi of the three known neutrino flavors. Additionally, we find that the correlation is even stronger if we include data in the 80 minute period before the arrival of the gravity wave signal. Given the large number of radionuclides whose decays are being monitored at any given time, we conjecture that other groups may also be in a position to search for statistically suggestive fluctuations of radionuclide decay rates associated with the GW170817 inspiral.

 

[mfb]

Given the large number of radionuclides whose decays are being monitored at any given time

... we should expect a 2.5 sigma deviation somewhere every day.

Needless to mention that the neutrino detectors didn't pick up anything.

 

[Vanadium 50]

Fischbach has a track record of finding dramatic new physics effects in other people's data - effects that subsequently are shown not to exist.

 

[alantheastronomer]

I was going to ask if the neutrino detectors observed anything from this event. mfb are you sure nothing was detected?

 

[mfb]

No neutrinos detected

 

[sophiecentaur]

No neutrinos detected

So, would we expect to detect some at a later time? (but not before lol.)

 

[mfb]

No, certainly not at a later time. They either come directly (even before visible light for supernovae) or not at all (in measurable amounts). There is no mechanism that would produce a large amount of slower neutrinos.

 

[snorkack]

Does neutron star merger produce neutrinos or antineutrinos?

 

[mfb]

Some for sure, and the following beta decays produce some more. But not enough for our detectors if the event is not close enough.

 

[Auto-Didact]

Pardo et al. 2018, Limits on the number of spacetime dimensions from GW170817

The observation of GW170817 in both gravitational and electromagnetic waves provides a number of unique tests of general relativity. One question we can answer with this event is: Do large-wavelength gravitational waves and short-frequency photons experience the same number of spacetime dimensions? In models that include additional non-compact spacetime dimensions, as the gravitational waves propagate, they "leak" into the extra dimensions, leading to a reduction in the amplitude of the observed gravitational waves, and a commensurate systematic error in the inferred distance to the gravitational wave source. Electromagnetic waves would remain unaffected. We compare the inferred distance to GW170817 from the observation of gravitational waves, dGWL, with the inferred distance to the electromagnetic counterpart NGC 4993, dEML. We constrain dGWL=(dEML/Mpc)γ with γ=1.01+0.04−0.05 (for the SHoES value of H0) or γ=0.99+0.03−0.05 (for the Planck value of H0), where all values are MAP and minimal 68% credible intervals. These constraints imply that gravitational waves propagate in D=3+1 spacetime dimensions, as expected in general relativity. In particular, we find that D=4.02+0.07−0.10 (SHoES) and D=3.98+0.07−0.09 (Planck). Furthermore, we place limits on the screening scale for theories with D>4 spacetime dimensions, finding that the screening scale must be greater than ∼20 Mpc. We also place a lower limit on the lifetime of the graviton of t>4.50×10^8 yr.

 

[lpetrich]

Does neutron star merger produce neutrinos or antineutrinos?

One has to look at what goes on in the merger.

Neutron-star material spewed out will be too neutron-rich to be stable at low pressures, so some of the neutrons will decay into protons, electrons, and antineutrinos.

If the neutron-star material gets hot enough, then it will glow in both ordinary neutrinos and antineutrinos.

As the two neutron stars merge, if they form a combined neutron star, then it may force some of its residual protons to become neutrons, releasing ordinary neutrinos.

 

[LURCH]

If I understand correctly, the total Shapiro delay is estimated around 2,000 days (I think I read somewhere that it was 1,800), and certain modified theories of GR predicted the difference in arrival times between gravity waves and EM radiation at around 1,000 days, right?

In any case, the difference in arrival time was less than these models predicted, but it was not zero. Any word on the cause of the 1.7 second delay? Is that a result of the event being originally shrouded by a cloud that temporarily resisted or impeded the release of EM, while allowing GW through? Or perhaps just dust and gas in the interstellar medium? Also, am I correct in understanding that pretty much everything is predicted to be transparent to GW’s?

I will have time in the next couple of days to read the articles above in their entirety, so apologies if these questions are already answered. (I got a bit excited)

 

[Matterwave]

Pardo et al. 2018, Limits on the number of spacetime dimensions from GW170817

I posted a Question about this on the physics stack exchange about why only gravity is expected to leak into these extra dimensions and got back an answer that basically said in String theory "closed strings" like gravity can leak but "open strings" like EM fields are confined to the 3+1 dim brane. I have say that such an explanation wasn't entirely satisfactory to me (but maybe I just don't know enough to understand the answer)...maybe some string theorist experts here could elaborate a bit more.