A Quasi-Anthropic Stringy Argue Why Nighttime Thing Is No Wimp?

Why my followers, moderate anthropic believers, may alone believe some anthropically sounding arguments

Brilliant physicist Bobby Acharya has tweeted near the media coverage, e.g. inwards Phys.ORG, of their Apr 2016 paper

The lightest visible-sector supersymmetric particle is probable to hold out unstable

that appeared in PRL 2 weeks ago.

The nighttime affair particle hasn't been straight detected on basis although it could guide maintain been. So the probability that it is a WIMP – a weakly interacting massive particle – has decreased. It hasn't decreased "spectacularly" but it has arguably decreased "visibly", past times a factor of 2 or something similar that. Dark affair may hold out composed of LIGO-style dark holes or axion-like ultralight scalars. Or it could spend upward to be – too some form of MOND, possibly amongst ideas analogous to Verlinde's recent speculations explaining it microscopically, could explicate the phenomena by too large attributed to nighttime matter.




But inwards the newspaper nosotros hash out now, Acharya, S. Ellis, G. Kane, B. Nelson, too M. Perry advise something else. The nighttime affair could hold out a superpartner but it's real probable that if string theory is right, it should hold out a superpartner of a particle that doesn't belong to the Standard Model. Not alone the nighttime affair particle hasn't been observed yet; its "original" superpartner isn't known yet, either.




So fifty-fifty though an LSP WIMP has been the preferred nighttime affair candidate of most supersymmetry phenomenologists too fifty-fifty though the spacetime supersymmetry is a characteristic of all realistic stringy descriptions of reality (claims to the reverse be but permit me non distract you), the authors claim that string theorists should truly believe that Nature does not purpose the pro-WIMP "cosmic coincidence".

To defend this proposition, they brand some observations near the spectrum of lite particle species inwards the string-theoretical vacua:

1. Almost all vacua inwards string theory – F-theory, M-theory, free-fermionic heterotic strings, too others – comprise hidden sectors, normally many of them.
2. These sectors may comprise particles too superpartners that may hold out lighter than the Standard Model particles too given the larger discover of the sectors too the absence of a argue why they shouldn't hold out lighter, the hidden sector particles that are lighter likely exist.
3. String theory seemingly unavoidably predicts nonzero interactions betwixt the Standard Model fields too those inwards the hidden sectors, peculiarly diverse \(F^{\rm SM}_{\mu\nu}F^{\mu\nu}_{\rm hidden}\) kinetic mixing of \(U(1)\) estimate fields. So the lightest Standard Model superpartner is probable to hold out allowed to decay to hidden sector particles too the decay proceeds much to a greater extent than chop-chop than at cosmological timescales.

It's a fun argumentation too I experience uncertain whether I should convey it seriously. Needless to say, the most problematic phrase is "most string vacua" which refers to typicality too some form of the anthropic principle. Is it acceptable?

One may convey this form of argumentation or spend upward it.

Moderate anthropicism

In the past, I guide maintain repeatedly suggested that I tin imagine that Nature prefers some "middle of the road" mental attitude to the anthropic reasoning. The total egalitarianism may hold out incorrect but "some arguments" of this flavour may hold out right.

Acharya's too pals' specific proposal helped me to articulate the "middle of the road" reasoning a chip to a greater extent than explicitly than e'er before. Why too how?

There's a argue why I don't purchase most arguments inwards the literature that claim that "we are generic" or "our cells guide maintain to hold out typical" or "our architecture of life is the most represented one" or "all vacua inwards string theory are as likely" – but why I tend to convey the Acharya et al. declaration to a greater extent than seriously. Do I guide maintain double standards?

I intend that in that place is a deviation betwixt the "most outrageous" examples of the reasoning based on typicality on 1 side; too this typicality of vacua that is used to deduce that the lightest Standard Model superpartner is unstable. What's the difference? Well, the deviation is that the vacua inwards the newspaper past times Acharya et al. are sufficiently similar to each other for us to care for them as a "nation" where everyone has the same right or a similar probability to hold out the foundation of the populace closed to us.

In to a greater extent than outrageous examples of the anthropic reasoning, this "democracy" has no expert argue too in that place may be real expert reasons why the people, stars, Boltzmann Brains, or whatever the anthropic radicals beloved to utter near are not as likely.



Group differences inwards ancient Rome

We may explicate these comments past times a political metaphor. Imagine that you lot discover yourself living inwards a woods inwards ancient Rome. You've forgotten near your previous life – who you lot are. And somebody asks you lot whether you lot are a patrician or a plebeian. He tells you lot that the numbers of members of these 2 groups are real different. Let's ignore the history too assume that the discover of plebeians was 100 times higher than the discover of patricians.

If you lot were a mindless anthropic believer who lives inwards the forest, you lot could similar a shot say that you lot are likely a plebeian – because the discover of plebeians is too hence much higher. But is it a valid reasoning? The argue why I don't discover it besides expert is that the plebeians too the patricians are real unlike groups. There was no democracy making them "equally valued". And inwards fact, alone the patricians formed the ruling bird too participated inwards the democracy. This "restricted democracy" is what I needed inwards the metaphor too why I picked ancient Rome as my example. (I didn't desire unproductive off-topic exchanges amongst fanatical defenders of women's suffrage, either LOL.)

This political deviation wasn't quite a airheaded coincidence. It has largely boiled to some innate or historical differences betwixt these 2 groups. (I don't desire to debate near the inquiry whether those statements were truly right inwards ancient Rome. You may certainly imagine a civilisation where they are right.) In particular, a patrician may hold out much to a greater extent than probable to intend near the validity of statistical arguments such as the quasi-anthropic declaration designed to "prove" that he is a plebeian. One argue is that you lot may guide maintain needed a training inwards statistics (in the past) to statistically intend at all too alone the patricians guide maintain received this training.

So I don't truly intend that it's right for you, a guy inwards the woods inwards ancient Rome, to conclude that you lot are likely a plebeian. The large discover of plebeians may hold out a positive argue to favor the stance that you lot are a plebeian. But in that place are arguments going inwards the opposite direction, too. One of them is that it's to a greater extent than probable for a patrician to carefully intend near such matters. And because you're thinking near them, it increases the probability that you lot are a patrician. It's non quite clear which of these 2 arguments – pushing the reply to opposite directions – is stronger if any. The right answers depend on a comparing of some numbers too those numbers aren't known, at to the lowest degree non accurately enough.

Analogously, when you're picking string vacua, the extreme anthropic believers desire to say that "all string vacua are as likely" too things similar that. So if they discover the largest grouping of string vacua – which is e.g. larger past times hundreds of thousands of orders of magnitude than others – their means of thinking makes them conclude that our populace must hold out 1 of those real numerous vacua.

I don't believe the determination too I intend that this whole means of thinking is fallacious. The argue is that each of the elements of the laid upward of vacua that has 10^272,000 elements may real good hold out near 10^500,000 times less probable than the elements of classes of vacua which guide maintain far fewer elements. The universe may guide maintain heavily punished these "plebeians" during the vacuum selection procedure because their existence plebeians is too hence visible. There's only no argue for this "group difference" non to exist. If the suppression past times 10^-500,000 exists, it's virtually impossible for your populace to hold out 1 of the 10^272,000 vacua, despite their high number.

You may encounter why I intend that the defenders of the radical anthropic regulation tend to hold out far left politically.

My betoken is the following. Whenever somebody uses a typicality argument, you lot should intend whether it is a

• "Lumo-indefensible typicality argument" or
• "Lumo-defensible typicality argument".

It's the erstwhile (invalid application of the anthropic reasoning) if the elements inwards the subset too its complement are "intrinsically or historically different", the differences is "immediately obvious" (you don't demand to hold off or run complicated tests to discover the difference), too in that place are expert reasons to intend that in that place mightiness hold out large "group differences" similar to the differences betwixt the plebeians too the patricians. It's the latter (tolerable application of the anthropic reasoning) if in that place are no mechanisms (or at to the lowest degree no known mechanisms) how the "group differences" could guide maintain evolved.

Acharya et al. are comparing vacua inwards a laid upward that does look similar the laid upward of patricians, a "politically uniform nation". If most of them guide maintain hidden sectors too sufficient interactions to destabilize the lightest Standard Model superpartners, you lot may translate this fact as a vote past times the patricians too you lot may desire to convey the final result seriously.

Isn't the stability of the lightest Standard Model superpartner a characteristic that divides the laid upward inwards the same means as the Romans may guide maintain been divided to patricians too plebeians? The reply is likely "No" because the decay of the Standard Model superpartners is a consequence of the selection of the vacua, something that decides near the distant future. But it is likely non a cause that has affected the real procedure of vacuum selection.

In other words, I desire to say that a to a greater extent than careful, weaker, Lumo-approved version of the anthropic regulation doesn't say that the probability that nosotros alive inwards the \(n\)-th vacuum is \(P_n={\rm const}\), a constant independent of \(n\) too fully determined past times \(\sum P_n = 1\). Instead, the probabilities \(P_n\) must hold out allowed to depend on some features of the \(n\)-th vacuum that could guide maintain reasonably too strongly affected the vacuum selection process, some real obvious "innate or historical grouping differences".

For example, \(P_n\) may hold out extremely pocket-size if \(n\) is a Calabi-Yau compactification amongst real high Hodge numbers – when a highly complex Calabi-Yau manifold is used for the hidden dimensions. Maybe, the development of the early on Universe demanded such a complex Calabi-Yau manifold to "evolve" too this achievement may hold out much to a greater extent than probable for Calabi-Yaus amongst depression Hodge numbers – too those may real good hold out favored, despite the pocket-size discover of elements inwards this set.

However, the holding that Acharya et al. "derive" past times their quasi-anthropic declaration is a "consequence" of some "technical details" describing each vacuum too non a reasonable campaign affecting the likelihood of a particular vacuum selection. They are comparing "patricians amongst other patricians" that guide maintain comparable Hodge numbers too other characteristics that are obvious to the naked eye.

And that's why I discover it reasonable to assign comparable probabilities \(P_n\) to all elements inwards the laid upward of vacua that Acharya et al. are comparing – too why I tend to hold out sympathetic to their argumentation too conclusions, too. The vacua only hold off similar citizens inwards an "innately or historically uniform nation" too when a large bulk of elements inwards such a laid upward guide maintain a sure property, 1 may believe that this holding is probable to concord for "you" when you lot desire to know "who you lot are" too "where you lot come upward from".