Gamma-ray bursts as QG signal

[marcus]

In the usual BH model, evaporation ends in a final flare and the possibility has been studied that a class of gamma-ray bursts, the VERY SHORT ones (VSGRB) could represent final explosions of PRIMORDIAL black holes (PBH).
http://inspirehep.net/record/901360?ln=en

When quantum corrections are taken into account one gets a different model of PBH evaporation and different predictions concerning final explosions.
http://arxiv.org/abs/1401.6562
As in the usual model, the evaporation lifetime depends on the initial mass, but in addition the total energy of the explosion and photons comprising it also depend on the initial mass!

See for example equation (22) on page 4 of the paper cited. Taking QG into account, the final mass, when the BH explodes, is estimated at about 70% of the initial mass.

This clearly has observational consequences. It's a different story with the usual BH model, where the final flash only comes when the BH has almost completely evaporated and can involve only a very limited amount of energy.

VSGRB appear to be a separate class, statistically, and to require a separate explanation from other GRB. One explanation that has been considered is that they're exploding PBH.
http://arxiv.org/abs/arXiv:1105.5363
Do Very Short Gamma Ray Bursts originate from Primordial Black Holes? Review
David B. Cline, Stan Otwinowski, Bozena Czerny, Agnieszka Janiuk
(Submitted on 26 May 2011)
We present the state of current research of Very Short Gamma Ray Bursts (VSGRBs) from seven GRB detectors. We found that VSGRBs form distinct class of GRBs, which in our opinion, in most cases can originate from the evaporating Primordial Black Holes (PBHs). Arguments supporting our opinion:
1. GRBs with time duration (T90) < 100 ms form distinct class: VSGRBs.
2. We observe significant anisotropy in the galactic angular distribution of BATSE VSGRB events.
3. V/Vmax distribution for BATSE VSGRB events indicates the local distance production.
4. VSGBBs have more energetic γ-ray burst than other GRBs with longer duration (KONUS).
5. We observe small number of afterglows in SWIFT VSGRB sample (25%), in contrast with the noticeable afterglow frequency in SGRB sample (78%).
6. Time profile of rising part BATSE VSGRBs is in agreement with the evaporation PBH model.
12 pages, 10 figures

Here's one of several earlier papers on this topic:
http://inspirehep.net/record/577330?ln=en
http://arxiv.org/abs/astro-ph/0110276
Evidence for a Galactic Origin of Very Short Gamma Ray Bursts and Primordial Black Hole Sources
D.B. Cline, C. Matthey, S. Otwinowski
(Submitted on 11 Oct 2001)
We systematically study the shortest time duration gamma ray bursts and find unique features that are best interpreted as sources of a galactic origin. There is a significant angular asymmetry and the V/Vmax distribution provides evidence for a homogenous or Euclidean source distribution. We review the arguments that primordial black hole evaporation can give such GRBs. The rate of events is consistent with a PBH origin if we assume on enhanced local density, as are the other distributions. We suggest further tests of this hypothesis.
10 pages, 4 figures, published in Astroparticle Physics. 18 (2003) 531-538

 

[marcus]

the Loop dark matter story

An essential part of the Loop Dark Matter story is the TINY SIZE OF primordial BH constituting clouds of DM.

One of these PBH is so small that it could pass through your body as if you were empty space.

A typical dark matter PBH might mass around a billion metric tonnes

That is the mass of a modest-size asteroid, or a cube of ice one kilometer on a side. The Schwarzschild radius of such a thing is inconceivably small.

 

[marcus]

An interesting side to the Loop dark matter scenario is that the rare explosions of these objects as they reach end-of-life would very gradually increase over time. Because the more massive ones take longer to reach the end of their evaporation phase and have a larger final mass.

The lifetime (before explosion) goes as the cube of the initial mass. The final mass (which converts to gamma ray energy) is about 70% of the initial mass. So dark matter PBHs in the distant future will have brighter terminal flashes. The size of current flashes (and the dominant photon energys/wavelengths) should be predictable.

Source: http://arxiv.org/abs/1401.6562

 

[marcus]

I find this 2011 pre-print by Cline et al very interesting especially when combined with the RV model of black hole (the "planck star" version), so will re-copy for easy reference:

http://arxiv.org/abs/arXiv:1105.5363
Do Very Short Gamma Ray Bursts originate from Primordial Black Holes? Review
David B. Cline, Stan Otwinowski, Bozena Czerny, Agnieszka Janiuk
(Submitted on 26 May 2011)
We present the state of current research of Very Short Gamma Ray Bursts (VSGRBs) from seven GRB detectors. We found that VSGRBs form distinct class of GRBs, which in our opinion, in most cases can originate from the evaporating Primordial Black Holes (PBHs). Arguments supporting our opinion:
1. GRBs with time duration (T90) < 100 ms form distinct class: VSGRBs.
2. We observe significant anisotropy in the galactic angular distribution of BATSE VSGRB events.
3. V/Vmax distribution for BATSE VSGRB events indicates the local distance production.
4. VSGBBs have more energetic γ-ray burst than other GRBs with longer duration (KONUS).
5. We observe small number of afterglows in SWIFT VSGRB sample (25%), in contrast with the noticeable afterglow frequency in SGRB sample (78%).
6. Time profile of rising part BATSE VSGRBs is in agreement with the evaporation PBH model.
12 pages, 10 figures

According to the sample calculation given in the RV paper ( http://arxiv.org/abs/1401.6562 ) the Planck star version PBH evaporates normally via Hawking radiation until its mass gets down to
sqrt (1/2) of the original mass--when it explodes in a gamma-ray burst.

since the lifespan of BH goes as the cube of the initial mass this mean that the final 35% of the conventional lifespan is lopped off, that being the fraction (sqrt(1/2))³.

This means that we can predict the absolute magnitude of the VSGRB which should be occurring in the present era. If the Planck star model is correct then the VSGRB should correspond to the explosion of a mass of around a billion metric tons, according to Rovelli Vidotto's calculation. They also give a representative GAMMA WAVELENGTH that would theoretically be produced, given their model of the PBH that would be exploding at this point in expansion history.

 

[marcus]

The question arises as to how abundant primordial black holes (PBH) would be, according to the Rovelli Vidotto "planck star" model, if they should happen account for most of the dark matter in the solar neighborhood.

There are various estimates of dark matter density at our distance from Galactic center ranging from 0.2 to 1.3 GeV/cm^3.

If we take a benchmark of 0.6 GeV/cm^3, this corresponds in metric terms to a mass density of 10^-12 kg in a cubic kilometer.

So how much DM mass would there be in a cube 100 million km on a side? That distance is comparable to the orbital radius of Venus about 2/3 of an astronomical unit . Obviously that volume would be expected to contain on average 10^12 kg, or a billion metric tons.

This is the smallest PBH now existing, according to the RV paper, because the lifespan of less massive ones will have already run out.

So if dark matter consists of primordial black holes, a cube 100 million km on a side would contain at most one of them, according to the sample calculation in the Planck star paper.

 

[MTd2]

This is from an old thread :marcus

http://arxiv.org/abs/1007.1317
Black holes in an asymptotically safe gravity theory with higher derivatives
Yi-Fu Cai, Damien A. Easson
22 pages, 3 figures
(Submitted on 8 Jul 2010)
"We present a class of spherically symmetric vacuum solutions to an asymptotically safe theory of gravity containing high-derivative terms. We find quantum corrected Schwarzschild-(anti)-de Sitter solutions with running gravitational coupling parameters. The evolution of the couplings is determined by their corresponding renormalization group flow equations. These black holes exhibit properties of a classical Schwarzschild solution at large length scales. At the center, the metric factor remains smooth but the curvature singularity, while softened by the quantum corrections, persists. The solutions have an outer event horizon and an inner Cauchy horizon which equate when the physical mass decreases to a critical value. Super-extremal solutions with masses below the critical value correspond to naked singularities. The Hawking temperature of the black hole vanishes when the physical mass reaches the critical value. Hence, the black holes in the asymptotically safe gravitational theory never completely evaporate. For appropriate values of the parameters such stable black hole remnants make excellent dark matter candidates."

Earlier this year Easson co-authored a couple of cosmology papers with Nobel laureate George Smoot. He and Cai have some interesting things to say here.

One helpful extra feature of the paper is that it gives a concise summary of the present situation in A.S. research. We have been following AS here at PF Beyond forum since 2006 or so. It has come a long way since then and it's nice to have a fresh perspective overview from someone like Easson who is new to it.
__________________

Here is an excerpt from the Introduction on page 2 of the Cai Easson paper:

One of the most challenging tasks facing theoretical physicists today is the construction of a consistent ultraviolet (UV) complete theory of gravity. Weinberg has suggested that the effective quantum field description of a gravitation theory may be UV complete and non-perturbatively renormalizable by virtue of asymptotic safety (AS) [1]. In this scenario the renormalization group (RG) flows have a fixed point in the UV limit and a finite dimensional critical surface of trajectories approach this point at short distances. This theory has been extensively studied in the literature [2–9], and recent evidence suggests the UV critical surface is only three-dimensional even in truncations of the exact RG equations with more than three independent coupling parameters [10–15]. Until now, the majority of the work on the subject has considered significant truncations of the action, taking into account only the Einstein-Hilbert and occasionally cosmological constant terms. In this paper, we initiate the study of black hole solutions in an asymptotically safe gravity theory including higher derivative terms and running gravitational couplings...

We've discussed some of this. Weinberg's July 2009 talk at CERN where he pointed out to the many string theorists in the audience that string might not be needed and might not be "how the world is" because of asymptotic safety (his original idea back in 1976). UV complete gravity + "good old" QFT, as he put it. His own research at that point was using AsymSafety to explain cosmological inflation without needing some exotic inflaton field---just by the running of couplings.*

Now Cai Easson seem to be trying to explain dark matter using running couplings, without needing to invoke some exotic new particle. It seems like an ambitious and risky proposal, but they claim it is testable.

FWIW I still lean towards thinking of dark matter as some particle, which will in due time be determined, but why reject Cai Easson's idea as long as what they say is right about it's being testable?

In any case somebody had to initiate the study of black holes under the assumption of AsymSafe gravity.

*If anyone wants links to the video of Weinberg's July 2009 CERN talk and his recent paper on cosmology with asymsafe gravity, please say. They are easy to find but I'd be glad to fetch them.

 

[marcus]

Hi MTd2,
the link to that 2010 thread (now closed) is https://www.physicsforums.com/showthread.php?t=414973
in case anyone wants to go back and read the comments.
I see it has 18 posts
6 by you
4 by Finbar
4 by me
3 by atyy
1 by Justin Levy

It's not directly related to the topic of gammaray bursts as signature of a QG theory, so it doesn't seem appropriate to discuss the paper here. You could start a separate thread, if you'd like to discuss it some more.
In Cai Easson's version of BH, evaporation leaves a cold remnant. I forget how they suggest the idea could be tested.
The Cai Easson paper generated some interest. I see it has 21 cites.
A recent review of BH in the AsymSafe context would be:

http://arxiv.org/abs/1401.4452
Black holes within Asymptotic Safety
Benjamin Koch, Frank Saueressig
(Submitted on 17 Jan 2014)
Black holes are probably among the most fascinating objects populating our universe. Their characteristic features found within general relativity, encompassing spacetime singularities, event horizons, and black hole thermodynamics, provide a rich testing ground for quantum gravity ideas. We review the status of black holes within a particular proposal for quantum gravity, Weinberg's asymptotic safety program. Starting from a brief survey of the effective average action and scale setting procedures, an improved quantum picture of the black hole is developed. The Schwarzschild black hole and its generalizations including angular momenta, higher-derivative corrections and the implications of extra dimensions are discussed in detail. In addition, the quantum singularity emerging for the inclusion of a cosmological constant is elucidated and linked to the phenomenon of a dynamical dimensional reduction of spacetime.
42 pages; Invited review for International Journal of Modern Physics A

It doesn't really fit in here, but if you are interested in cold black hole remnants in the AsymSafe context you should definitely start a thread on it and bring us up to date!
==============
EDIT: AHHH! I see what you might be driving at! Not the gammarayburst angle but the dark matter angle.

At least on the basis of a first look, I have to discard the idea that PBH could be an important contribution to dark matter (in the Planck star version). There would be too many flashes occurring and there would be too bright a gammaray background. So the dark matter story works in AsymSafe context (you pointed out) but it does not work in the Rovelli Vidotto Planck star context.
The Planck star picture of BH has other motivations: resolve the BH information paradox, explain certain types of GRB…
But it does not seem to be a viable candidate for explaining what DM could consist of.

 

[MTd2]

Yes, too many flashes. Unless they'd be at equilibrium with the CMB. And, they could had exploded mostly on the ionization era. We couldn't likely detect, but it would sprinkle many nano black holes. You see, the density of the plank star is too high, much higher than the usual black holes, so, if they decompose, the can pack again in those nano black holes, forever stable.

 

[marcus]

Anyone following this investigation of a new concept of BH might want to print off a fresh copy of
http://arxiv.org/abs/1401.6562 because version 4 is out, as of a few days ago.

The 17 January Koch Saueressig paper that I pointed to a couple of posts back was added to their references ("Black Holes within Asymptotic Safety" see post #7 this thread) as also were a couple of others co-authored by Sabine Hossenfelder, who is thanked in the acknowledgments for extended discussions of the first draft.

To be a bit more precise about the SIZE of gamma ray bursts that should be occurring at present if the Rovelli Vidotto model is correct and applies to primordial BHs, it turns out that to have a lifespan just under 14 billion years the BH initial mass should be:

one fifth gigaton

that is, 0.2 x 10⁹ metric tons, or 0.2 x 10¹² kilograms.

By Rovelli Vidotto's reckoning this leads to a lifespan of 13.9 billion years, approximately the expansion age of the universe. And the FINAL MASS is then the original one fifth gigaton divided by √2, namely about one seventh gigaton. So let's work that out in JOULES of gamma ray burst energy.
".14e12 kg*c^2" into google gives 1.26 x 10²⁸ joules (aka 1.26 x 10³⁵ ergs)
This will give a handle on the absolute luminosity of the resulting GRB.

One of the Cline et al papers I linked to earlier has this:
"One way to detect PBHs is by their Hawking radiation, when they evaporate (“explode”) at present. The properties of PBH burst emission are model dependent and were estimated [3] for γ- ray burst in the range of tens of ms with luminosity ~ 10³³ erg."

Some more links from the same Cline et al paper:
[9]. D.B. Cline et al., “The Search for Primordial Black Holes Using Very Short Gamma Ray Bursts”, http://arxiv.org/abs/0704.2398.
[10]. B. Czerny et al., “Observational Constraints on the Nature of Very Short Gamma-Ray Bursts”, New Astronomy in press, http://arxiv.org/abs/1006.1470.
[11]. B.J. Carr et al., “New Cosmological Constraints on Primordial Black Holes”, http://arxiv.org/abs/0912.5297.