Friday, October 30, 2015

Recent Updates and Some Recent Silly Headlines

It's been a few months. So, here are some updates:

(1) Dark matter did not kill off the dinosaurs. This is just silly. Dark matter is likely warm, and not cold, and hence doesn't clump. So, it can't be blamed for killing off the dinosaurs.

(2) China can't sustain 7%/yr growth rates when its interest rates are only 4.35%. Second, if you lower interest rates, you don't promote growth rates. Think about it. How can you improve the growth rate on your investments when you are willing to accept low rates of return from your portfolio?

(3) China's "social credit score" is creepy and downright authoritarian. Don't protest against the government or else they will lower your "social credit score." Be a good citizen and don't mind the fact that you can't vote us out of office!

(4) I no longer believe that dark energy can be explained by decaying dark matter. Instead, dark energy is likely just the vacuum energy density of the Higgs field. The expectation energy value, φ, of the Higgs field is 246 GeV, but we don't know what is the vacuum energy density V(φ).
V(φ) could be pretty much any value.
As proposed by  Mikhail Shaposhnikov, the Higgs field could be both the source of inflation and dark energy...depending on the value of known particles, such as the top quark, W boson, and Higgs boson.

(4) The case for Warm Dark Matter is even stronger. A recent paper by Garzilli and Boyarsky shows that the Lyman Alpha forest data (previously used by Viel et al. 2013 to rule out certain warm dark matter candidates) is actually pointing towards a rest mass for dark matter of ~3 keV. (Though, values greater than 3 keV are still within 1 sigma uncertainty. So, this is not an actual detection.) The point here is that Viel et al. 2013 likely did not model the temperature of the Intergalatic Medium (IGM) correctly, and likely overestimated the temperature of the IGM at large z (especially given that the value of the reionization optical depth and the z for reionization dropped significantly in the 2015 Planck results, and will likely decrease even further in future Planck data releases. A likely value for the optical depth is 0.06 rather than 0.078 quotes back in 2013 or 0.068 in 2015.) To be somewhat fair to Viel et al, they did point out in Figure 10 of their paper that the temperature at high z comes out low if they allow the temperature to flout at high z, but for their presented results, they did not allow the temperature to drop below 5000K at z=5.4.
  The results from Garzilli and Boyarsky are summarized below.

The figure above shows that a value of 3 keV appears to be consistently the best option at all four values of z. The temperature of the IGM appears to increase from <5000 10="" at="" greater="" than="" to="" z="4.2.</p">
The figure above shows the flux power spectrum of the Lyman Alpha Forest. Note the cut off in power spectra at a wavenumber of ~0.06 s/km. Viel et al. 2013 has previously understood the cut off to be due to a high temperature of the IGM. However, according to Garzilli and Boyarsky 2015, these results can be better described by a 3 keV dark matter particle and a lower temperature IGM. Note also that a 3 keV thermal relic dark matter particle is quite similar to a 7 keV sterile neutrino made with a lepton asymmetry of 0.000001. (See figure 5 of the Garzilli and Boyarsky manuscript.)