The cosmological constant doesn’t do anything to the universe. A math equation can’t “boost the expansion”.

This “expansion” has gone through many changes in physics theories over the years.

First, in 1916, Einstein said all the stars were “fixed” and the universe was neither expanding nor contracting.

Then in 1927, Lemaitre introduced the big bang “fireworks” theory (as it was called by Eddington in 1932) and he said the expansion began from a “point”.

Next it was an “expansion” not from a “point”, but from a large “pre-existing” sphere (Eddington’s own theory in the 1930s).

Einstein changed his mind and accepted the Hubble observations as evidence of an “expansion”, but in the 1940s Hubble denied the redshifts indicated an “expansion” (I learned this from a leaflet sent to me by the Mt. Wilson observatory).

For about 20 years, the “expansion” was supposed to have taken place at a “steady rate”, but in the early 1950s, all of a sudden the theory changed to include “sudden inflation”, so the universe suddenly expanded greatly in the beginning (but never faster than light speed), and then it “slowed down” to its present (1950s) rate.

Then later, the theory changed from Eddington’s “pre-existing sphere” model, back to Lemaitre’s “big bang” fireworks model, with everything starting off at a “point”.

Then later, the theory changed again, saying the “inflation” was a time when everything in the universe “expanded faster than the speed of light”, and then it slowed down to its present (1990s) rate.

And now, some astronomers say it’s “slowing down”, while other say it’s “speeding up”.

See this NASA website:

“This means that 2 billion years ago, the universe was expanding a bit faster than it is today, and so the universe is slowing down in its expansion as it gets OLDER.”

NASA SOURCE

Now see this different NASA website:

“Expansion of Universe Was Once Sluggish, Now Speeding Up: Astronomers Report Cosmic Growth Spurts”

NASA SOURCE

So, the real truth is, they just don’t know what it’s doing, and they never did know.