Thomas Dent
May30-04, 05:24 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>I apologise for any confusion in the thread(s) - Google Groups doesn\'t\nseem to be able to retrieve the previous messages so I\'m barred from\nwriting a followup.\n\nUrs Schreiber <Urs.Schreiber@uni-essen.de> wrote\n\n> Supersymmetric Unification Without Low Energy Supersymmetry And Signatures\n> for Fine-Tuning at the LHC\n>\n> hep-th/0405159\n>\n> the authors argue that the apparent fine-tuning of the cosmological\n> constant dwarfs most other fine-tunings that one encounters so that from\n> this point of view it is, after all, not unreasonable to assume a finely\n> tuned light Higgs while SUSY is broken at high energies.\n\nThis is a bad argument if made without further qualification. If the\nstatement is "Fine tuning - who cares?" then the strong CP problem,\nSUSY flavour and CP problems, and even proton decay, which all involve\nfine-tuning certain parameters to be very small, are no longer\nproblems, and the usual low-energy SUSY models are not in any trouble,\nso we should not prefer high-energy SUSY. But I suppose this is not\nwhat the authors actually meant.\n\n> They argue that the "atomic principle" (stable atoms should\n> exist) or even the stronger "Carbonic principle" (Carbon should exist)\n> as selection principles together with some "scanning mechanism" (e.g.\n> eternal inflation) of some parameter "landscape" do suggest such a fine\n> tuning without any need for low energy susy.\n\nThis is different: it is to say that we should not care about any\nfine-tuning that can be treated by an "X-ic principle", where X is\nanthro, atom, or carbon. But we should care about other types of\nfine-tuning that are not amenable to such a principle. This makes more\nsense, since the SUSY flavour and CP problems, and the exceptionally\nlong proton lifetime, are not affected by any "X-ic principle" that we\nknow of, and remain as serious problems for low-energy SUSY.\n\nBut such an "X-ic principle" is also dangerous, because it may not be\ncorrect. The correct thing to use is the observer selection principle,\nas explained by Nick Bostrom. That is, we should discard universes\nthat do not contain beings able to observe the kind of fact we are\nconsidering (e.g. the large size of the universe).\n\nThen the authors face the task of proving that no such observers could\never arise, in universes where the Higgs vev is larger by some factor\nthan it is in ours. To do this they would have to search the entire\nhistory of such universes. Iff they could show that in all (or the\ngreat majority of) such cases the history of the universe was\npredictable and had no observers, it could work.\n\nI strongly doubt that this can be done, given the extreme difficulty\nin explaining the emergence of intelligent observers in our universe.\nAs Dyson said, the only thing we definitely and unequivocally require\nfor intelligent observerhood is the ability to process a lot of\ninformation, on the level of a universal computer. This does not rule\nout, for example, a universe that is a simple cellular automaton, or\nan assemblage of long-lived black holes that instantiate a Turing\nmachine, as long as the universe is large enough.\n\nSo I don\'t believe that any "X-ic principle" can deal with the Higgs\nsector - only the cosmological constant, a la Weinberg.\n\n> As far as I see, of these successes the authors mention two, namely gauge\n> coupling unification and lightest superpartners as good candidates for\n> dark matter.\n>\n>(...) Are these two potential advantages all that keeps people from\n> considering models with _no_ susy in 4 dimensions?\n\nMany people have indeed considered non-SUSY models. With respect to\ndark matter, they can be more or less as good as SUSY, e.g. in TeV\ncompactifications there may be a lightest K-K particle, in "little\nHiggs" there may be dark matter candidates. They drop out more or less\nas naturally as the neutralino does.\n\nWith respect to unification, nothing is as predictive as SUSY-GUT or\nN=1 heterotic, which gives SUSY its advantage. (See e.g. Ghilencea and\nRoss from a few years ago.) SUSY-GUT or heterotic don\'t give quite the\ncorrect answer for the strong coupling. Still, if one imposes that\ncorrections to the first, not quite right, answer, are small, and that\nthe predictions are not fine-tuned with respect to the free parameter\nthat comes into the corrections, one can still maintain the statement\nthat SUSY-GUT/heterotic are the only models where one can meaningfully\ncompare unification prediction with experiment. I haven\'t looked at\nwhether high-scale SUSY can be equally predictive.\n\nSome phenomenologists will tell you the biggest success for SUSY was\npredicting the top mass, because of electroweak symmetry-breaking\nthrough top loops. In contrast to dark matter, the top has actually\nbeen seen. High-scale SUSY would of course throw away any preference\nfor a heavy top.\n\nAnd of course non-SUSY models don\'t solve the hierarchy problem\n(consistently with EW precision data), which to most physicists, and\nto me, is a real problem which cannot be made to go away by\n"principles".\n\nWith respect to string models (here I am on less solid ground)\nnon-SUSY models are difficult to make consistent, because of not\nsolving the EOM, i.e. tadpoles, or tachyons. SUSY string models of\ncourse have to deal with moduli, but this is seen as less bad,\nespecially in the light of recent developments.\n\nDine\'s most recent paper hep-th/0405190 offers the argument that\nnon-SUSY models with compactified extra dimensions (to be precise\nthose where all fermions have antiperiodic b.c. around at least one\nextra dimension having topology S^1) are vulnerable to destruction by\nWitten\'s "bubble of nothing", hence probably do not describe the world\nwe live in. (There is also the Fabinger-Horava decay of non-SUSY\nM-theory on S^1/Z_2.) However, this does not distinguish between low-\nand high-energy SUSY-breaking, as long as the fermions do the right\nthing to prevent the bubble.\n\n\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>I apologise for any confusion in the thread(s) - Google Groups doesn't
seem to be able to retrieve the previous messages so I'm barred from
writing a followup.
Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
> Supersymmetric Unification Without Low Energy Supersymmetry And Signatures
> for Fine-Tuning at the LHC
>
> http://www.arxiv.org/abs/hep-th/0405159
>
> the authors argue that the apparent fine-tuning of the cosmological
> constant dwarfs most other fine-tunings that one encounters so that from
> this point of view it is, after all, not unreasonable to assume a finely
> tuned light Higgs while SUSY is broken at high energies.
This is a bad argument if made without further qualification. If the
statement is "Fine tuning - who cares?" then the strong CP problem,
SUSY flavour and CP problems, and even proton decay, which all involve
fine-tuning certain parameters to be very small, are no longer
problems, and the usual low-energy SUSY models are not in any trouble,
so we should not prefer high-energy SUSY. But I suppose this is not
what the authors actually meant.
> They argue that the "atomic principle" (stable atoms should
> exist) or even the stronger "Carbonic principle" (Carbon should exist)
> as selection principles together with some "scanning mechanism" (e.g.
> eternal inflation) of some parameter "landscape" do suggest such a fine
> tuning without any need for low energy susy.
This is different: it is to say that we should not care about any
fine-tuning that can be treated by an "X-ic principle", where X is
anthro, atom, or carbon. But we should care about other types of
fine-tuning that are not amenable to such a principle. This makes more
sense, since the SUSY flavour and CP problems, and the exceptionally
long proton lifetime, are not affected by any "X-ic principle" that we
know of, and remain as serious problems for low-energy SUSY.
But such an "X-ic principle" is also dangerous, because it may not be
correct. The correct thing to use is the observer selection principle,
as explained by Nick Bostrom. That is, we should discard universes
that do not contain beings able to observe the kind of fact we are
considering (e.g. the large size of the universe).
Then the authors face the task of proving that no such observers could
ever arise, in universes where the Higgs vev is larger by some factor
than it is in ours. To do this they would have to search the entire
history of such universes. Iff they could show that in all (or the
great majority of) such cases the history of the universe was
predictable and had no observers, it could work.
I strongly doubt that this can be done, given the extreme difficulty
in explaining the emergence of intelligent observers in our universe.
As Dyson said, the only thing we definitely and unequivocally require
for intelligent observerhood is the ability to process a lot of
information, on the level of a universal computer. This does not rule
out, for example, a universe that is a simple cellular automaton, or
an assemblage of long-lived black holes that instantiate a Turing
machine, as long as the universe is large enough.
So I don't believe that any "X-ic principle" can deal with the Higgs
sector - only the cosmological constant, a la Weinberg.
> As far as I see, of these successes the authors mention two, namely gauge
> coupling unification and lightest superpartners as good candidates for
> dark matter.
>
>(...) Are these two potential advantages all that keeps people from
> considering models with _no_ susy in 4 dimensions?
Many people have indeed considered non-SUSY models. With respect to
dark matter, they can be more or less as good as SUSY, e.g. in TeV
compactifications there may be a lightest K-K particle, in "little
Higgs" there may be dark matter candidates. They drop out more or less
as naturally as the neutralino does.
With respect to unification, nothing is as predictive as SUSY-GUT or
N=1 heterotic, which gives SUSY its advantage. (See e.g. Ghilencea and
Ross from a few years ago.) SUSY-GUT or heterotic don't give quite the
correct answer for the strong coupling. Still, if one imposes that
corrections to the first, not quite right, answer, are small, and that
the predictions are not fine-tuned with respect to the free parameter
that comes into the corrections, one can still maintain the statement
that SUSY-GUT/heterotic are the only models where one can meaningfully
compare unification prediction with experiment. I haven't looked at
whether high-scale SUSY can be equally predictive.
Some phenomenologists will tell you the biggest success for SUSY was
predicting the top mass, because of electroweak symmetry-breaking
through top loops. In contrast to dark matter, the top has actually
been seen. High-scale SUSY would of course throw away any preference
for a heavy top.
And of course non-SUSY models don't solve the hierarchy problem
(consistently with EW precision data), which to most physicists, and
to me, is a real problem which cannot be made to go away by
"principles".
With respect to string models (here I am on less solid ground)
non-SUSY models are difficult to make consistent, because of not
solving the EOM, i.e. tadpoles, or tachyons. SUSY string models of
course have to deal with moduli, but this is seen as less bad,
especially in the light of recent developments.
Dine's most recent paper http://www.arxiv.org/abs/hep-th/0405190 offers the argument that
non-SUSY models with compactified extra dimensions (to be precise
those where all fermions have antiperiodic b.c. around at least one
extra dimension having topology S^1) are vulnerable to destruction by
Witten's "bubble of nothing", hence probably do not describe the world
we live in. (There is also the Fabinger-Horava decay of non-SUSY
M-theory on S^1/Z_2.) However, this does not distinguish between low-
and high-energy SUSY-breaking, as long as the fermions do the right
thing to prevent the bubble.
seem to be able to retrieve the previous messages so I'm barred from
writing a followup.
Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote
> Supersymmetric Unification Without Low Energy Supersymmetry And Signatures
> for Fine-Tuning at the LHC
>
> http://www.arxiv.org/abs/hep-th/0405159
>
> the authors argue that the apparent fine-tuning of the cosmological
> constant dwarfs most other fine-tunings that one encounters so that from
> this point of view it is, after all, not unreasonable to assume a finely
> tuned light Higgs while SUSY is broken at high energies.
This is a bad argument if made without further qualification. If the
statement is "Fine tuning - who cares?" then the strong CP problem,
SUSY flavour and CP problems, and even proton decay, which all involve
fine-tuning certain parameters to be very small, are no longer
problems, and the usual low-energy SUSY models are not in any trouble,
so we should not prefer high-energy SUSY. But I suppose this is not
what the authors actually meant.
> They argue that the "atomic principle" (stable atoms should
> exist) or even the stronger "Carbonic principle" (Carbon should exist)
> as selection principles together with some "scanning mechanism" (e.g.
> eternal inflation) of some parameter "landscape" do suggest such a fine
> tuning without any need for low energy susy.
This is different: it is to say that we should not care about any
fine-tuning that can be treated by an "X-ic principle", where X is
anthro, atom, or carbon. But we should care about other types of
fine-tuning that are not amenable to such a principle. This makes more
sense, since the SUSY flavour and CP problems, and the exceptionally
long proton lifetime, are not affected by any "X-ic principle" that we
know of, and remain as serious problems for low-energy SUSY.
But such an "X-ic principle" is also dangerous, because it may not be
correct. The correct thing to use is the observer selection principle,
as explained by Nick Bostrom. That is, we should discard universes
that do not contain beings able to observe the kind of fact we are
considering (e.g. the large size of the universe).
Then the authors face the task of proving that no such observers could
ever arise, in universes where the Higgs vev is larger by some factor
than it is in ours. To do this they would have to search the entire
history of such universes. Iff they could show that in all (or the
great majority of) such cases the history of the universe was
predictable and had no observers, it could work.
I strongly doubt that this can be done, given the extreme difficulty
in explaining the emergence of intelligent observers in our universe.
As Dyson said, the only thing we definitely and unequivocally require
for intelligent observerhood is the ability to process a lot of
information, on the level of a universal computer. This does not rule
out, for example, a universe that is a simple cellular automaton, or
an assemblage of long-lived black holes that instantiate a Turing
machine, as long as the universe is large enough.
So I don't believe that any "X-ic principle" can deal with the Higgs
sector - only the cosmological constant, a la Weinberg.
> As far as I see, of these successes the authors mention two, namely gauge
> coupling unification and lightest superpartners as good candidates for
> dark matter.
>
>(...) Are these two potential advantages all that keeps people from
> considering models with _no_ susy in 4 dimensions?
Many people have indeed considered non-SUSY models. With respect to
dark matter, they can be more or less as good as SUSY, e.g. in TeV
compactifications there may be a lightest K-K particle, in "little
Higgs" there may be dark matter candidates. They drop out more or less
as naturally as the neutralino does.
With respect to unification, nothing is as predictive as SUSY-GUT or
N=1 heterotic, which gives SUSY its advantage. (See e.g. Ghilencea and
Ross from a few years ago.) SUSY-GUT or heterotic don't give quite the
correct answer for the strong coupling. Still, if one imposes that
corrections to the first, not quite right, answer, are small, and that
the predictions are not fine-tuned with respect to the free parameter
that comes into the corrections, one can still maintain the statement
that SUSY-GUT/heterotic are the only models where one can meaningfully
compare unification prediction with experiment. I haven't looked at
whether high-scale SUSY can be equally predictive.
Some phenomenologists will tell you the biggest success for SUSY was
predicting the top mass, because of electroweak symmetry-breaking
through top loops. In contrast to dark matter, the top has actually
been seen. High-scale SUSY would of course throw away any preference
for a heavy top.
And of course non-SUSY models don't solve the hierarchy problem
(consistently with EW precision data), which to most physicists, and
to me, is a real problem which cannot be made to go away by
"principles".
With respect to string models (here I am on less solid ground)
non-SUSY models are difficult to make consistent, because of not
solving the EOM, i.e. tadpoles, or tachyons. SUSY string models of
course have to deal with moduli, but this is seen as less bad,
especially in the light of recent developments.
Dine's most recent paper http://www.arxiv.org/abs/hep-th/0405190 offers the argument that
non-SUSY models with compactified extra dimensions (to be precise
those where all fermions have antiperiodic b.c. around at least one
extra dimension having topology S^1) are vulnerable to destruction by
Witten's "bubble of nothing", hence probably do not describe the world
we live in. (There is also the Fabinger-Horava decay of non-SUSY
M-theory on S^1/Z_2.) However, this does not distinguish between low-
and high-energy SUSY-breaking, as long as the fermions do the right
thing to prevent the bubble.