Paper 📜 day with @stephstem, Marc Kamionkowski, and @oliver_philcox! We have found that parity violation can be strongly imprinted in galaxies (and also the cosmic microwave background) through gravitational interactions in the early Universe. (1/n).

RT @just_shaun: Those interested in this talk, and parity violation in general, should check out the Parity Violation from Home conference….

RT @just_shaun: A Cosmology Talk!. Observations are flirting with the idea that parity might be violated on cosmological scales. But there….

RT @SimonsFdn: Congrats to the first class of Stony Brook Simons STEM Scholars! With support from Simons Foundation, these accomplished stu….

Overall, this project has been a great ride with @stephstem Marc and @oliver_philcox! Though there are still many more questions to answer: e.g. How does this signal look in the CMB? What about massless spin-1 particles? More concrete statements about baryogenesis? Stay tuned!🎉.

Our calculation is the first example of a parity-violating scalar trispectrum through interactions with a massless particle (the graviton) and its measurements can probe dCS in uncharted high-energy regimes. These dCS regimes can also potentially cause baryogenesis. (13/n).

And when I say much larger, I do mean in a potentially detectable manner! We consider 7 current, upcoming, and future spectroscopic galaxy and 21-cm surveys and find that they would be sensitive to models of dCS gravity (including our two examples). (12/n)

The standard dCS setup, though, yields a signal in galaxies that is too small to be detected. However, with modest modifications, we show two examples that lead to much larger signals! Our parameterization also allows for straightforward extensions to other modifications. (11/n)

We also find that the ratio of parity-even and -odd parts, in a particular limit, has a very simple relation that is described only by the degree to which both graviton polarizations are different, the graviton's spin, and an angle related to the 4-point's orientation. (10/n)

What we found is that, in dCS gravity, the 4-point function of inflaton variations (aka the scalar trispectrum) has a parity-odd (i.e. violating) part. The parity-even (i.e. preserving) part also exists and is the sum, rather than the difference, of graviton polarizations.(9/n)

How does this 4-point function relate to inflation? Remember inflation can explain the current galaxy distribution. How? Roughly by linking galaxy positions to spots where spatial variations of the inflaton δφ is large. So four galaxies can come from four such variations. (8/n).

Why four points? For two points in an isotropic Universe, a parity (P) flip is equivalent to a rotation (R). The same is true for three points, and this argument finally fails for four. (7/n)

Now that we know how parity-violation can arise in the early Universe, we return to the question: how can we see it? In galaxies, the easiest way is to consider the correlation of four points of galaxy positions. (6/n)

The graviton, like the photon, has two polarizations, h_+ and h_-, that are parity inverses of each other. Hence, parity violation occurs when the two exist in unequal amounts. The simplest model that causes such an existence is called dynamical Chern-Simons (dCS) Gravity. (5/n)

Minimal inflation models contain a field to cause the rapid acceleration, the inflaton φ, and the always-present gravitational analog of the photon, the graviton h . (4/n).

First, we must consider a concrete period of the early Universe to ask our first question. Here, we consider a period of rapid acceleration in the early Universe that could explain the current distribution of galaxies 🌌, also known as inflation. (3/n).

We know that the weak interactions already violate parity. Also, the early Universe must somehow violate a related parity in order to produce the baryon asymmetry we see today. It is natural to ask then: how can early-Universe parity-violation arise? How would we see it?🧐(2/n).

Parity, also known as mirror symmetry, is the flip of spatial coordinates across some axis ↔️. (2/n)