Exploring the Mystery of Matter/Antimatter Asymmetry in the Early Universe

[Randy Subers]

TL;DR Summary

Could the matter/antimatter asymmetry just be an initial condition

Is there anything in the current theoretical world that says that the universe has to have started with an equal amount of matter/antimatter, probably none at all and everything was created from photons. Could it be that there just happened to be a small amount of matter around or at least a small amount of matter exceeding the amount of antimatter at the start of the universe?

 

[Drakkith]

Yes, it's possible that the universe started with an asymmetry, but that's kind of a cop out. Theoretical predictions about the early universe usually have matter and radiation appearing from something like a state change or field transition as the early universe transitioned from a higher energy to a lower energy state. In such a case, conservation laws usually require that an equal amount of matter and antimatter be created.

 

[kimbyd]

Summary:: Could the matter/antimatter asymmetry just be an initial condition

Is there anything in the current theoretical world that says that the universe has to have started with an equal amount of matter/antimatter, probably none at all and everything was created from photons. Could it be that there just happened to be a small amount of matter around or at least a small amount of matter exceeding the amount of antimatter at the start of the universe?

Consider the model of inflation. During inflation, the universe is driven to be nearly completely empty. All of the matter we see comes from the end of inflation: when the inflaton field decays, it dumps its energy into standard-model particles. This initial decay would in the simplest models have led to equal numbers of particle/anti-particle pairs. Some process must explain the imbalance.

 

[ohwilleke]

Summary:: Could the matter/antimatter asymmetry just be an initial condition

Is there anything in the current theoretical world that says that the universe has to have started with an equal amount of matter/antimatter, probably none at all and everything was created from photons.

No.

Could it be that there just happened to be a small amount of matter around or at least a small amount of matter exceeding the amount of antimatter at the start of the universe?

Yes.

Physicist Sabine Hossenfelder explains this at greater length at her Backreaction blog, summarizing her analysis by stating:

The brief summary is that the matter antimatter asymmetry is a pseudo-problem. It can be solved by using an initial value that agrees with observations, and that’s that. Of course it would be nice to have a deeper explanation for that initial value. But within the framework of the theories that we currently have, such an explanation is not possible. You always have to choose an initial state, and you do that just because it explains what we observe. If a physicist tries to tell you otherwise, ask them where they get their initial state from.

There is no evidence based or experimentally established theory basis for the conclusion that the initial conditions of the Universe needed to have equal amounts of matter and antimatter. The laws of physics only provide that matter and antimatter creation must be equal in amount in events after any given set of initial conditions (with small exceptions not large enough to account for the observed differences).

Indeed, the sum total of the observational evidence that we have and the experimentally established theories that we have point to the conclusion that the initial conditions of the universe had more matter than antimatter. The mainstream view among physicists, although there are some theorists http://www.helsinki.fi/~donofrio/2011_07_Princeton_donofrio.pdf, is that Standard Model sphaleron processes in the twenty minutes during which Big Bang Nucleosynthesis is believed to have taken place, or the preceding ten seconds between the Big Bang and the onset of Big Bang Nucleosynthesis, can't account for the massive asymmetry between baryons made of matter and baryonic anti-matter that is observed in the universe (also here) without beyond the Standard Model physics (also here). Likewise, after that point, sphaleron processes should be so rare that they can't explain the baryon asymmetry of the universe. For example, this recent paper on CP violation said:

The realization of CP violation in weak interactions has been established in the K- and B-meson systems by several experiments, and all results are well interpreted within the CKM formalism. However, the size of CP violation in the SM appears to be too small to account for the observed matter-antimatter asymmetry,

- R. Aaij et al. (LHCb Collaboration), "Observation of CP Violation in Charm Decays." 122 Phys. Rev. Lett. 211803 (May 29, 2019).

Matt Strassler, another physicist who blogs, likewise acknowledge that using general relativity and the Standard Model to extrapolate from the existing universe backward in time only as far as those theories have been validated experimentally, or at least by a consensus very well motivated theoretical argument to extend those theories from the region where they have been validated experimentally, does not take you all of the way back to a Big Bang singularity.

There is really nothing more arbitrary about assuming that the initial conditions of the observable universe had more matter than antimatter, than there is about assuming that the initial conditions of the observable universe had non-zero aggregate mass-energy.

If one wants a theory that could preserve some kind of global matter-antimatter symmetry without contradicting the observational evidence, there is a body of theoretical research supposing that there may be an anti-universe with an equal and opposite matter-antimatter asymmetry in the opposite time direction from our own universe from the Big Bang. See, e.g., February 18, 2020 paper, March 23, 2018 paper, and June 20, 2017 paper.

 

[PeterDonis]

In such a case, conservation laws usually require that an equal amount of matter and antimatter be created.

Usually, but not always. We know of CP violating processes that could create unequal amounts of matter and antimatter. However, as I understand it, our best present estimates are that these processes alone are not enough to account for the matter-antimatter imbalance we actually observe.

 

[ohwilleke]

Usually, but not always. We know of CP violating processes that could create unequal amounts of matter and antimatter. However, as I understand it, our best present estimates are that these processes alone are not enough to account for the matter-antimatter imbalance we actually observe.

Fair point that I was editing in.

 

[ohwilleke]

Consider the model of inflation. During inflation, the universe is driven to be nearly completely empty. All of the matter we see comes from the end of inflation: when the inflaton field decays, it dumps its energy into standard-model particles. This initial decay would in the simplest models have led to equal numbers of particle/anti-particle pairs. Some process must explain the imbalance.

Why?

If inflation can only exist in a world where there are equal numbers of particle and anti-particle pairs, maybe that subset of the hundreds of extant inflation theories are wrong. Theories need to flow from observation and not the other way around. If a theory leads to inferences inconsistent with what we know, we have to tentatively reject it. And, we certainly have no direct evidence of the nature of any hypothetical inflaton field. Perhaps inflaton fields can only decay to matter and not antimatter. That is no more absurd a property than the well established one that W bosons only interact with left parity particles. Problem solved.

 

[ohwilleke]

Yes, it's possible that the universe started with an asymmetry, but that's kind of a cop out. Theoretical predictions about the early universe usually have matter and radiation appearing from something like a state change or field transition as the early universe transitioned from a higher energy to a lower energy state. In such a case, conservation laws usually require that an equal amount of matter and antimatter be created.

Those theoretical predictions usually flow from the arbitrary axiom that the matter-antimatter balance was exactly equal at t=0 that has no evidence to support it. The cop out is insisting that the universe have theoretically beautiful properties that are contrary to observational evidence.

 

[PeterDonis]

If inflation can only exist in a world where there are equal numbers of particle and anti-particle pairs

The post you were responding to didn't say that. It only said that "in the simplest models" equal numbers of particles and antiparticles would be created at reheating (not equal numbers of pairs--each pair by itself contains a particle and an antiparticle).

 

[PeterDonis]

the arbitrary axiom that the matter-antimatter balance was exactly equal at t=0 that has no evidence to support it

In inflation models, until the end of inflation, all of the Standard Model fields are in their vacuum states, with zero particles. That state obviously has equal numbers of particles and antiparticles--zero of each.

 

[ohwilleke]

The post you were responding to didn't say that. It only said that "in the simplest models" equal numbers of particles and antiparticles would be created at reheating (not equal numbers of pairs--each pair by itself contains a particle and an antiparticle).

So, to be more exactly, the simplest models of inflation referred to are ruled out. More complex models merely point out that since there are so many moving parts in inflation theory that we can't know what the pre-inflation initial conditions were because we don't know what theory to apply and have no observational means of distinguishing them. Nothing gets us back to an matter-antimatter balance that is supported by any positive evidence.

 

[ohwilleke]

In inflation models, until the end of inflation, all of the Standard Model fields are in their vacuum states, with zero particles. That state obviously has equal numbers of particles and antiparticles--zero of each.

Again. If an inflation model implies an equal amount of particles and antiparticles at its conclusion, whether it is zero or a zillion, it is inconsistent with observational evidence and must be wrong. The imbalance has to exist at the same time as or before Standard Model physics kicks in, and by the time that the universe has conditions about which we have any observational evidence.

 

[PeterDonis]

the simplest models of inflation referred to are ruled out.

Only if there is no other mechanism for creating a matter-antimatter asymmetry after reheating is complete. But we don't know that that's the case.

If an inflation model implies an equal amount of particles and antiparticles at its conclusion, whether it is zero or a zillion, it is inconsistent with observational evidence

Same comment as above.

The imbalance has to exist at the same time as or before Standard Model physics kicks in

Not necessarily, since Standard Model physics might not be complete in all energy regimes since reheating.

One can certainly make a plausibility argument that developing the assumed amount of asymmetry after reheating, assuming no asymmetry at reheating, is unlikely. But that's a weaker claim than "ruled out".

 

[ohwilleke]

The initial question in this thread is:

Could the matter/antimatter asymmetry just be an initial condition

The answer is still clearly "yes" it could, and any answer to the contrary has to invoke beyond the Standard Model physics theories that have no observational support.

 

[PeterDonis]

The answer is still clearly "yes" it could, and any answer to the contrary has to invoke beyond the Standard Model physics theories that have no observational support.

Asymmetry in the initial condition also has no observational support, plus it contradicts our expectation from the same Standard Model physics, which says that reheating should create particle-antiparticle pairs, which must result in equal numbers of particles and antiparticles.

The "it could" answer is of course possible, but I'm not sure its current observational support is any stronger than the contrary answer. This is a regime in which our understanding is still very, very tentative.

 

[PeterDonis]

the universe has to have started with an equal amount of matter/antimatter, probably none at all and everything was created from photons

At least for inflation models, this is not quite correct. Before the end of inflation, all of the energy in the universe was in the inflaton field; all of the Standard Model fields were in their vacuum states (no particles at all), including the photon (actually the photon field would not have been present then since it only appears after electroweak symmetry breaking, but the general point remains). At the end of inflation, the "reheating" process (misnamed since there was no previous time at which any "heating" of the Standard Model fields had occurred) transferred the energy from the inflaton field to all of the Standard Model fields (which, at this extremely high temperature, were all massless, so they all would have had approximately equal energy density). Transfer of energy between Standard Model fields occurred later, as the universe expanded and cooled.

 

[ohwilleke]

Asymmetry in the initial condition also has no observational support, plus it contradicts our expectation from the same Standard Model physics, which says that reheating should create particle-antiparticle pairs, which must result in equal numbers of particles and antiparticles.

The "it could" answer is of course possible, but I'm not sure its current observational support is any stronger than the contrary answer. This is a regime in which our understanding is still very, very tentative.

Asymmetry in the initial condition is what you get when you take current conditions and all known Standard Model processes and the follow them back as far as it is possible to do so. There is no Standard Model process that gets you to equality in the required time frame.

Standard Model physics should not create that expectation. It is a theory about how we go from one state in time to a future state in time, it doesn't have any axioms or assumptions about initial conditions.

If your theory of the early Universe requires a different condition at the time when Standard Model physics apply (and we don't need any additions to the Standard Model all of the way up to the GUT scale for it to be mathematically consistent and anomaly free), then the evidence we have so far suggests that this theory is wrong and somebody needs to go back to the drawing board and consider the reheating scenario proposed.

If your theory goes back to before the domain of applicability of the Standard Model (which begins very early after the Big Bang, about 10^-12 seconds after the Big Bang in the canonical chronology of the universe), then all bets are off and we are really not doing science anymore, just making unprovable conjectures that don't deserve serious attention until we have more available data to distinguish between the myriad possibilities.

 

[kimbyd]

Again. If an inflation model implies an equal amount of particles and antiparticles at its conclusion, whether it is zero or a zillion, it is inconsistent with observational evidence and must be wrong. The imbalance has to exist at the same time as or before Standard Model physics kicks in, and by the time that the universe has conditions about which we have any observational evidence.

The matter/anti-matter imbalance is generally thought to arise later, after reheating.

It's technically possible for reheating itself to result in the imbalance, but that amounts to the same problem: what is the specific CP violation which resulted in the asymmetry in the first place? After all, if inflaton decay results in a matter/anti-matter imbalance, then inflaton decay is a CP-violating process. So, what is that process?

If you're wondering why I'm referring to CP violation, CP refers to the combination of charge and parity. This is the specific symmetry which relates matter to anti-matter: a spin-up electron becomes a spin-down positron under this symmetry.

As mentioned earlier, we do know of some processes which violate charge-parity symmetry (such as the decay of the neutron kaon $K^0$). But their magnitudes are simply too small to cause the observed imbalance between matter and anti-matter. It is expected that other as-yet-unknown processes are the culprit.

If you're wondering if the inflaton itself might make up the matter/anti-matter imbalance, in order to do that the inflaton would need to not be its own anti-particle. And its mass would need to be at the right value to explain the imbalance. I'm not sure that's possible given current observations. But if it were possible, that would also be interesting.

 

[ohwilleke]

It is expected that other as-yet-unknown processes are the culprit.

The thing is, once we are in the quark era, i.e. 10^-12 seconds after the Big Bang in the canonical chronology of the universe, we have reached conditions that we have observed at the LHC and in "natural" colliders that we can observe with astronomy observations, and we haven't observed any of these "as-yet-unknown processes." Indeed, the highest energies directly observable in the Large Hadron Collider take us back to the era preceding the "quark era" to the "electroweak epoch".

So, if there is some new as-yet-unknown processes that are unknown because they are limited to high energies, there is a time span of one trillionth of a second after the Big Bang in which they can arise. After that, we know that there are no such processes so the matter-antimatter imbalance has to be present by then.

For purposes of what we can do with Standard Model physics and observationally tested science, we can't go back further than the first trillionth of a second after the Big Bang and conditions then are our de facto initial conditions. Anything earlier than that is an educated guess with nothing to back it up at best.

 

[PeterDonis]

Asymmetry in the initial condition is what you get when you take current conditions and all known Standard Model processes and the follow them back as far as it is possible to do so.

But it's not what you get when you take the condition at the end of inflation and apply the known Standard Model to the reheating process. So we are clearly missing something somewhere.

Again, this is a regime where our understanding is very, very tentative, which means that any pronouncements about what is "ruled out" or what does or does not have something to back it up are premature.

 

[PeterDonis]

if there is some new as-yet-unknown processes that are unknown because they are limited to high energies, there is a time span of one trillionth of a second after the Big Bang in which they can arise

One trillionth of a second is still a very, very long time given the time scales of the processes we are talking about. It also spans many, many orders of magnitude in temperature. So your implication that nothing of interest could happen during this time is not justified.

 

[ohwilleke]

But it's not what you get when you take the condition at the end of inflation and apply the known Standard Model to the reheating process. So we are clearly missing something somewhere.

The problem with that analysis is that we can only work backwards.

We can't just assume some particular set of initial conditions and an inflation theory, or for that matter a reheating process, that is inconsistent with the laws of physics in the domain of applicability where the laws of physics have been empirically tested. Indeed, the evidence for any particular inflation theory or of inflation as the only possible solution for the observations that inflation explains is not exceptionally strong or precisely. We've narrowed down the parameter space for possible inflation theories a lot, but the evidence for it is hardly solid than the evidence we have about how much CP violation occurs at LHC energies or less.

Any time you work forward from a proposed set of initial conditions and laws of physics and that doesn't get you to where you are on solid ground from working backwards, you are doing it wrong. Somewhere in the pool of possibilities is a correct answer, but we are in a situation where that answer is not just unknown but unknowable at the moment.

 

[Drakkith]

Those theoretical predictions usually flow from the arbitrary axiom that the matter-antimatter balance was exactly equal at t=0 that has no evidence to support it. The cop out is insisting that the universe have theoretically beautiful properties that are contrary to observational evidence.

I disagree that our theoretical predictions using a symmetrical matter-antimatter initial condition are necessarily inconsistent with observational evidence.

We can't just assume some particular set of initial conditions and an inflation theory, or for that matter a reheating process, that is inconsistent with the laws of physics in the domain of applicability where the laws of physics have been empirically tested.

Yes we can. If we are looking into a time where the universe is believed to be in a state that is beyond the applicability of the standard model, then we can do whatever we want.

Indeed, the evidence for any particular inflation theory or of inflation as the only possible solution for the observations that inflation explains is not exceptionally strong or precisely.

No one is saying inflation is the only possible solution. I don't know why you believe this.

Any time you work forward from a proposed set of initial conditions and laws of physics and that doesn't get you to where you are on solid ground from working backwards, you are doing it wrong.

Oh nonsense. It is perfectly reasonable to work forward from theoretical initial conditions and see what you're model gets you, even if that model gets you something that doesn't make sense at the time. The only time you're wrong is when you try to say that your model is correct and it can't have been another way. No one is saying that about any theory or model current in use by science. Even a grossly incorrect model or theory is useful in the sense of telling scientists, "This probably isn't the right way of going forward."

 

[PeterDonis]

The problem with that analysis is that we can only work backwards.

Not at all. We can both work backwards from observations, using some particular model, and work forwards from an assumed initial condition, using some particular model.

Of course different theorists will have different preferences; your preference appears to favor the "backwards" mode. But your preference is not the same as an absolute requirement.

We can't just assume some particular set of initial conditions and an inflation theory, or for that matter a reheating process, that is inconsistent with the laws of physics

We don't know the complete laws of physics. So there is no way of enforcing your requirement. We can say what our currently known laws of physics predict, but our currently known laws of physics are not the same as "the" laws of physics.

in the domain of applicability where the laws of physics have been empirically tested.

Since, as you have already said, this domain only goes back so far, we cannot apply this prescription further back than that. See next comment.

Any time you work forward from a proposed set of initial conditions and laws of physics and that doesn't get you to where you are on solid ground from working backwards, you are doing it wrong.

You have already said that the Standard Model can only take us backwards so far. We can't apply this prescription further back than that, and "further back than that" includes the end of inflation in inflation models.

we are in a situation where that answer is not just unknown but unknowable at the moment.

If this is true, then, as I have already said, pronouncements about what is "ruled out" or about what does or does not have something to back it up are not justified. So you should stop making such pronouncements.

 

[kimbyd]

The thing is, once we are in the quark era, i.e. 10^-12 seconds after the Big Bang in the canonical chronology of the universe, we have reached conditions that we have observed at the LHC and in "natural" colliders that we can observe with astronomy observations, and we haven't observed any of these "as-yet-unknown processes." Indeed, the highest energies directly observable in the Large Hadron Collider take us back to the era preceding the "quark era" to the "electroweak epoch".

So? Reheating happened at at least ten orders of magnitude more energy than we can currently access at the LHC. It would be positively shocking if there weren't processes new processes to discover somewhere in that range.

Hell, we can't even say with confidence that we've observed everything at the energies the LHC has accessed, either. Because the LHC collides protons, the collisions are incredibly dirty. There may be things going on there that we have the data for, but simply haven't been able to separate from the background noise yet.

The LHC was intended to be followed up with a linear collider which probes the same general energy scale, the ILC. But that never happened due to budget cuts. This collider would have used electrons, producing much cleaner reactions with much higher signal-to-noise. They're still trying to get a similar project off the ground. Hopefully sometime soon.

 

[ohwilleke]

Not at all. We can both work backwards from observations, using some particular model, and work forwards from an assumed initial condition, using some particular model.

Of course different theorists will have different preferences; your preference appears to favor the "backwards" mode. But your preference is not the same as an absolute requirement.We don't know the complete laws of physics. So there is no way of enforcing your requirement. We can say what our currently known laws of physics predict, but our currently known laws of physics are not the same as "the" laws of physics.Since, as you have already said, this domain only goes back so far, we cannot apply this prescription further back than that. See next comment.You have already said that the Standard Model can only take us backwards so far. We can't apply this prescription further back than that, and "further back than that" includes the end of inflation in inflation models.If this is true, then, as I have already said, pronouncements about what is "ruled out" or about what does or does not have something to back it up are not justified. So you should stop making such pronouncements.

There is some point, it looks like t=10^-12, but maybe somebody thinks it is really t=10 minutes, where we are at energies in which the only thing we have to assume is that the laws of physics at a given energy are the same as they are today, at which we have reasonable certainty. We can deduce that there is asymmetry by that point in time . We can't have Big Bang Nucleosynthesis, for example, at a state of matter-antimatter asymmetry.

We can say what our currently known laws of physics predict, but our currently known laws of physics are not the same as "the" laws of physics.

We can't be sure of them up to infinite energy scales, but we can be pretty darn comfortable about them in their proven domain of applicability.

And., I think @kimbyd is way too pessimistic about what we know already. We know enough to dramatically curtail the magnitude and nature of what we don't know. If we've seen absolutely no evidence of BSM physics of some kind at one energy scale, there won't be overwhelming evidence of it "just around the corner" at slightly higher energy levels. High energy physics is too interconnected for that to happen. So, the cutoff point is necessarily fuzzy. The bigger the change from New Physics, the higher the energies at which it has to occur.

Yes, there is a gap of t=0 to this cutoff point at which all bets are off, we have no idea what the laws of physics are, we have no direct observations.

All we know is that the New Physics from t=0 to this cutoff point in the very early universe needs due to the early Universe physics, old or new, need to dovetail to the known physics a little bit later. If inflation has consequences, those consequences need to have manifested by that point. If there is new source of matter-antimatter asymmetry, it needs to have manifested by then.

Now, as long as you can come up with New Physics that gets you from t=0 to this cutoff with the right conditions at the cutoff, you're all good.

f your proposed New Physics at ultra high early Universe energies doesn't get you to where you get from solid ground, however, you have a problem.

But it's not what you get when you take the condition at the end of inflation and apply the known Standard Model to the reheating process. So we are clearly missing something somewhere.

In order words, something about the conditions at the end of inflation or the beyond proven range of applicability Standard Model reheating process is wrong. That's what "we are clearly missing something somewhere" means. We may not be sure how it is wrong, but we know we need to keep looking for physics that can meet our minimum requirements.

Oh nonsense. It is perfectly reasonable to work forward from theoretical initial conditions and see what you're model gets you, even if that model gets you something that doesn't make sense at the time. The only time you're wrong is when you try to say that your model is correct and it can't have been another way. No one is saying that about any theory or model current in use by science. Even a grossly incorrect model or theory is useful in the sense of telling scientists, "This probably isn't the right way of going forward."

If you work forward from theoretical initial conditions until you get to the point where we have observations and physical laws within their domain of applicability, yes, your theory really is wrong. Maybe you weren't trying to get it right. But it really doesn't seems so outlandish to think that we should devote more attention to models that work or come close to working than to models that don't come remotely close. It's like the vacuum energy paradox. We know that something about the way that is formulates is grossly out of touch with reality so we need to be thinking about the problem very differently rather than continuing down that path.

We do have a wildly under-constrained theory space of possible New Physics.

We have almost no experimental data to guide us. We have assumed as an axiom that the laws of nature that we know and love might not work, maybe even probably won't work. But, we can at least start discounting the theories that don't get us where we need to get and pay more attention to the ones that do.

Is there any other legitimate, scientific, way to prefer one option over another?

So, for example, if we think we need inflation and we are just convinced for no really defensible reason that t=0 has equal amounts of matter and antimatter, we should be much more favorably inclined to an inflaton that gives rise to matter-antimatter asymmetry, than to one that does not, because the CP violation in the CKM matrix and PMNS matrix isn't going to cut it to accomplish those ends.

We can take "no new physics" back well beyond the experimentally proven domain of applicability of the Standard Model and see what initial conditions that will give us. This is something we can do. It doesn't carry the same proven certainty, but it is hard to see any other better baseline to compare other theories to.

We could also take the position that we ought to look for the keys we lost under the streetlight, because that's the best we can do at the moment.

Or, maybe we ought to be able to acknowledge, in much the same way that we do about what lies beyond the event horizon in a black hole, or what exists beyond the observable Universe, that there are somethings that are just intrinsically unknowable.

The central point is all of this, however, is that no axioms uncorroborated by data are entirely to any deference just because we think that they are beautiful. If we get axioms that produce good results and they are also beautiful, swell. But, right now, we have some quite ugly theories that get the job done and there is no good reason to believe that the provable discoverable scientific truth will ever get prettier.

Ideas like "naturalness", "fine tuning", and resorts to Platonic ideals that we pull out of our butts, are not science. The idea that we have to start at matter-antimatter balance at t=0 has nothing to back it up. The idea that there should be strong force CP violation has nothing to back it up. We shouldn't presume to know what the laws of nature should look like. Going down that road is a waste of time and effort that has failed over and over and over again for decades now.

 

[kimbyd]

And., I think @kimbyd is way too pessimistic about what we know already. We know enough to dramatically curtail the magnitude and nature of what we don't know. If we've seen absolutely no evidence of BSM physics of some kind at one energy scale, there won't be overwhelming evidence of it "just around the corner" at slightly higher energy levels. High energy physics is too interconnected for that to happen. So, the cutoff point is necessarily fuzzy. The bigger the change from New Physics, the higher the energies at which it has to occur.

Except that we're not talking about "just around the corner". It would be really really nice if new physics was "just around the corner" because then we would start to see its impacts in terrestrial experiments soon!

We're talking about ten+ orders of magnitude in energy. Some radically different things could be happening at a single order of magnitude higher energy than we've directly probed and we'd have little chance of having any evidence of it.

Perhaps more to the point, I'm not even sure that we need anything terribly exotic to explain the matter/anti-matter imbalance. We might just need a number of new resonances like the neutral kaon that we simply haven't observed yet. And those might even have masses of no more than hundreds of GeV. Perhaps there are theoretical reasons why this is not possible I'm unaware of. My knowledge of the field is limited. But they are detecting new instances of CP violation at the LHC, such as the $\Lambda_b$ decay. That there are new such things to discover is virtually guaranteed.

The question is whether these and similar processes will add up to the observed imbalance. That remains to be seen.

 

[Drakkith]

But, we can at least start discounting the theories that don't get us where we need to get and pay more attention to the ones that do.

But it really doesn't seems so outlandish to think that we should devote more attention to models that work or come close to working than to models that don't come remotely close.

To my knowledge there simply aren't any theories or models that work any better than what we already have. That's the problem. Our current models using inflation don't work perfectly? Well neither does anything else!