Lubos Motl
Oct31-04, 07:47 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>This posting is about the new paper by Gia Dvali:\n\nhttp://www.arxiv.org/abs/hep-th/0410286\n\nThere are also other interesting papers on the web, but this one, I think,\nwill attract the attention of many people.\n\nGia Dvali joined Nima Arkani-Hamed and Savas Dimopoulos, friends (applied\nstring theorists) who are his co-fathers of the large extra dimensions,\nand proposed his own version of an anthropically inspired solution of the\nhierarchy problem.\n\nRecall that Nima and Savas have proposed Split supersymmetry\n\nhttp://arxiv.org/abs/hep-th/0405159\n\nthat argues that it\'s OK if the Higgs is unnatural and tuned, but with\nthis single sacrifice, one may argue that SUSY should be broken at a high\nscale and gluinos (dark matter) should be the only light superpartners,\nwhich also preserves the success of gauge coupling unification.\n\nGia Dvali\'s approach has similar goals and methods, but different\n"details". Gia\'s scenario is based on these rather simple ideas:\n\n1. The Higgs mass is effectively a dynamical quantity, which arises from\nan interaction with a 4-form field strength F4 (the term is Higgs^2.F4^2)\ninduced by some heavy domain walls (2-branes)\n\n2. This mass is dynamical, but discrete. To solve the hierarchy problem,\none needs to find a reason why the small masses are preferred. Gia follows\nMichael Douglas\'s anthropic counting where the number of vacua measures\nhow natural something is - but in a one-parameter family of vacua only,\nwhich may be more meaningful.\n\nGia\'s explanation why the small mass is preferred is a kind of "beauty is\nattractive" argument. It seems that he just postulates that the density of\nvacua diverges around the desired point because of a power law - without\nshowing why the exponent has the correct sign etc.\n\n(This does not look quite satisfactory to me. You can always say that\nsomething XY is small because there is some underlying approximate\nsymmetry that changes XY by a factor, which effectively makes\nlog(parameter) a more natural quantity, and "parameter" is then expected\nto be much smaller. Is it an explanation? To be more quantitative, I\ndon\'t know how he gets 10^{-16} as opposed to 10^{-infinity}, for\nexample.)\n\nHe says that the required symmetry to make the small mass an "attractor"\nis a brane conjugation symmetry; he argues that a second Higgs doublet is\nneeded; and he surprisingly relates the Higgs physics with the QCD scale;\nalso, he claims that the quarks\' Yukawa couplings are then severely\nconstrained. All these statements may be very interesting.\n\nI have not had time to study all these points in detail yet, but I hope\nthat someone will write her or his understanding.\n__________________________________ ____________________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)\nWebs: http://schwinger.harvard.edu/~motl/ http://motls.blogspot.com/\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>This posting is about the new paper by Gia Dvali:
http://www.arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0410286
There are also other interesting papers on the web, but this one, I think,
will attract the attention of many people.
Gia Dvali joined Nima Arkani-Hamed and Savas Dimopoulos, friends (applied
string theorists) who are his co-fathers of the large extra dimensions,
and proposed his own version of an anthropically inspired solution of the
hierarchy problem.
Recall that Nima and Savas have proposed Split supersymmetry
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0405159
that argues that it's OK if the Higgs is unnatural and tuned, but with
this single sacrifice, one may argue that SUSY should be broken at a high
scale and gluinos (dark matter) should be the only light superpartners,
which also preserves the success of gauge coupling unification.
Gia Dvali's approach has similar goals and methods, but different
"details". Gia's scenario is based on these rather simple ideas:
1. The Higgs mass is effectively a dynamical quantity, which arises from
an interaction with a 4-form field strength F4 (the term is Higgs^2.F4^2)
induced by some heavy domain walls (2-branes)
2. This mass is dynamical, but discrete. To solve the hierarchy problem,
one needs to find a reason why the small masses are preferred. Gia follows
Michael Douglas's anthropic counting where the number of vacua measures
how natural something is - but in a one-parameter family of vacua only,
which may be more meaningful.
Gia's explanation why the small mass is preferred is a kind of "beauty is
attractive" argument. It seems that he just postulates that the density of
vacua diverges around the desired point because of a power law - without
showing why the exponent has the correct sign etc.
(This does not look quite satisfactory to me. You can always say that
something XY is small because there is some underlying approximate
symmetry that changes XY by a factor, which effectively makes
log(parameter) a more natural quantity, and "parameter" is then expected
to be much smaller. Is it an explanation? To be more quantitative, I
don't know how he gets 10^{-16} as opposed to 10^{-infinity}, for
example.)
He says that the required symmetry to make the small mass an "attractor"
is a brane conjugation symmetry; he argues that a second Higgs doublet is
needed; and he surprisingly relates the Higgs physics with the QCD scale;
also, he claims that the quarks' Yukawa couplings are then severely
constrained. All these statements may be very interesting.
I have not had time to study all these points in detail yet, but I hope
that someone will write her or his understanding.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)
Webs: http://schwinger.harvard.edu/~motl/ http://motls.blogspot.com/
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
http://www.arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0410286
There are also other interesting papers on the web, but this one, I think,
will attract the attention of many people.
Gia Dvali joined Nima Arkani-Hamed and Savas Dimopoulos, friends (applied
string theorists) who are his co-fathers of the large extra dimensions,
and proposed his own version of an anthropically inspired solution of the
hierarchy problem.
Recall that Nima and Savas have proposed Split supersymmetry
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0405159
that argues that it's OK if the Higgs is unnatural and tuned, but with
this single sacrifice, one may argue that SUSY should be broken at a high
scale and gluinos (dark matter) should be the only light superpartners,
which also preserves the success of gauge coupling unification.
Gia Dvali's approach has similar goals and methods, but different
"details". Gia's scenario is based on these rather simple ideas:
1. The Higgs mass is effectively a dynamical quantity, which arises from
an interaction with a 4-form field strength F4 (the term is Higgs^2.F4^2)
induced by some heavy domain walls (2-branes)
2. This mass is dynamical, but discrete. To solve the hierarchy problem,
one needs to find a reason why the small masses are preferred. Gia follows
Michael Douglas's anthropic counting where the number of vacua measures
how natural something is - but in a one-parameter family of vacua only,
which may be more meaningful.
Gia's explanation why the small mass is preferred is a kind of "beauty is
attractive" argument. It seems that he just postulates that the density of
vacua diverges around the desired point because of a power law - without
showing why the exponent has the correct sign etc.
(This does not look quite satisfactory to me. You can always say that
something XY is small because there is some underlying approximate
symmetry that changes XY by a factor, which effectively makes
log(parameter) a more natural quantity, and "parameter" is then expected
to be much smaller. Is it an explanation? To be more quantitative, I
don't know how he gets 10^{-16} as opposed to 10^{-infinity}, for
example.)
He says that the required symmetry to make the small mass an "attractor"
is a brane conjugation symmetry; he argues that a second Higgs doublet is
needed; and he surprisingly relates the Higgs physics with the QCD scale;
also, he claims that the quarks' Yukawa couplings are then severely
constrained. All these statements may be very interesting.
I have not had time to study all these points in detail yet, but I hope
that someone will write her or his understanding.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)
Webs: http://schwinger.harvard.edu/~motl/ http://motls.blogspot.com/
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^