Lubos Motl
Dec5-04, 07:54 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>Today I vote for Christos Kokorelis\' paper\n\nhttp://www.arxiv.org/abs/hep-th/0412035\n\nIt seems that the intersecting braneworlds have become pretty viable. In\nthis paper, Christos studies type IIA, T^6 / (Z_3 x Z_3) orbifold plus\norientifold models, with D6-branes not being parallel to the O6-planes.\nThis orbifold structure has so far not been studied in the intersecting\nbraneworld context, as far as I understand. This type of orbifold fixes\nall the complex structure moduli, just by requiring the Z_3 symmetries.\n\nThe Z_3 x Z_3 orbifolding is producing a singular Calabi-Yau, which has\nN=2 SUSY with type IIA, and the orientifold planes break it to N=1. The\nD6-branes are then wrapped in various other directions, and anomaly\ncancellation is a constraint.\n\nA model starting with a 9-generation N=1 model can lead to a *pure*\n3-generation N=0 standard model at low energies (below the string scale\nwhich is comparable to the GUT scale). The people who hate new physics -\nlike Peter Woit - should read the previous sentence twice: it is really a\n*pure* Standard Model below the string/Planck scale. Moreover, in some\nsense, Christos could argue that the model *predicts* three generations\nalthough he seems probably able to construct less simple\nhigher-generation models, too.\n\nVarious conditions expected from the SUSY GUT theories are reproduced\nalthough it is not a SUSY or GUT theory - the squared sin of the Weinberg\nangle is 3/8. It\'s sort of surprising that this fact appears from so many\nnon-GUT models - it is a much more general fact about such realistic\ntheories that "explain" the origin of the Standard Model. alpha2 equals\nalpha3 quite naturally, but the real issue is how the hypercharge is\nnormalized, and it often works like in GUT. For another example of the\nfeatures that his models satisfy, Christos argues that some of these\nmodels satisfy the assumption of split supersymmetry.\n\nHe can also define models that give you pure Pati-Salam models, pure GUTs\n(SU(5) and flipped SU(5)), and so forth. In all these intersecting\nbraneworlds, the right-handed neutrino is necessary for anomaly\ncancellation, and the nature of the Higgs is a bit confusing.\n\nIt\'s not a good idea to copy the paper here. Instead, we should initiate a\ndiscussion. I personally see two main reasons why these models look more\nattractive than the flux vacua:\n\n1. They avoid the religion of the uncalculable vast landscape\nof nonlinear sigma models, that naturally leads many to believe the\nanthropic feelings. The "number" of the intersecting brane models\nis sort of "nicely countable". Physics behind them is a nice theory of\nfree fields on the worldsheet, which seems perfectly sufficient to\ngenerate life. I don\'t promote simplicity for the sake of itself,\nbut especially because the existence and properties of these models\nare easier to be verified. The flat space - coming from T^6 - sort of\nsounds more naturally to me than curved Calabi-Yaus with huge\ncurvature, especially because we know that the curvature in the large\n4 dimensions is so tiny.\n\n2. They have a natural explanation for the exponential hierarchy of the\nfermion masses. (Even though Christos comments that there may be\ngeneral problems to get the upper quarks\' masses at all.) Well, maybe\nthis is only the case of the models that represent the Higgs\ndifferently from the present models of Christos. In Christos\' models\ntoday, he really derives the exponential form of the masses mainly for\nthe higgsinos.\n\nIt\'s not yet quite clear to me how the Kahler moduli and the D-brane\npositions are really stabilized in these models.\n\nSome advocates of the anthropic flux vacua can argue that they are better\nin solving the cosmological constant problem because these N=1 models give\nyou a wrong C.C. Well, I would buy Christos\' approach to isolate the\nC.C. problem - a very low energy problem, related to NS-NS tadpoles etc.\nin his model - from the rest of particle physics. Outside string theory,\nthe particle physicists study particle physics independently of the\nquestion of the C.C. String theory unifies everything, so we can\'t really\nisolate two questions completely - but on the other hand, there is a class\nof many TeV (and higher) questions whose answer should not be biased by\nour attempts to understand something at the sub-eV scale.\n\nThe intersecting models give a pretty simple and natural description of\nparticle physics, and I find it unconvincing to replace them with less\nnatural and less controllable models only for the sake of explaining one\nparticular very-low-energy dimensionful number, namely the vacuum energy\ndensity. Feel more than free to disagree and respond.\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</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>Today I vote for Christos Kokorelis' paper
http://www.arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0412035
It seems that the intersecting braneworlds have become pretty viable. In
this paper, Christos studies type IIA, T^6 / (Z_3 x Z_3) orbifold plus
orientifold models, with D6-branes not being parallel to the O6-planes.
This orbifold structure has so far not been studied in the intersecting
braneworld context, as far as I understand. This type of orbifold fixes
all the complex structure moduli, just by requiring the Z_3 symmetries.
The Z_3 x Z_3 orbifolding is producing a singular Calabi-Yau, which has
N=2 SUSY with type IIA, and the orientifold planes break it to N=1. The
D6-branes are then wrapped in various other directions, and anomaly
cancellation is a constraint.
A model starting with a 9-generation N=1 model can lead to a *pure*
3-generation N=0 standard model at low energies (below the string scale
which is comparable to the GUT scale). The people who hate new physics -
like Peter Woit - should read the previous sentence twice: it is really a
*pure* Standard Model below the string/Planck scale. Moreover, in some
sense, Christos could argue that the model *predicts* three generations
although he seems probably able to construct less simple
higher-generation models, too.
Various conditions expected from the SUSY GUT theories are reproduced
although it is not a SUSY or GUT theory - the squared sin of the Weinberg
angle is 3/8. It's sort of surprising that this fact appears from so many
non-GUT models - it is a much more general fact about such realistic
theories that "explain" the origin of the Standard Model. alpha2 equals
alpha3 quite naturally, but the real issue is how the hypercharge is
normalized, and it often works like in GUT. For another example of the
features that his models satisfy, Christos argues that some of these
models satisfy the assumption of split supersymmetry.
He can also define models that give you pure Pati-Salam models, pure GUTs
(SU(5) and flipped SU(5)), and so forth. In all these intersecting
braneworlds, the right-handed neutrino is necessary for anomaly
cancellation, and the nature of the Higgs is a bit confusing.
It's not a good idea to copy the paper here. Instead, we should initiate a
discussion. I personally see two main reasons why these models look more
attractive than the flux vacua:
1. They avoid the religion of the uncalculable vast landscape
of nonlinear \sigma models, that naturally leads many to believe the
anthropic feelings. The "number" of the intersecting brane models
is sort of "nicely countable". Physics behind them is a nice theory of
free fields on the worldsheet, which seems perfectly sufficient to
generate life. I don't promote simplicity for the sake of itself,
but especially because the existence and properties of these models
are easier to be verified. The flat space - coming from T^6 - sort of
sounds more naturally to me than curved Calabi-Yaus with huge
curvature, especially because we know that the curvature in the large
4 dimensions is so tiny.
2. They have a natural explanation for the exponential hierarchy of the
fermion masses. (Even though Christos comments that there may be
general problems to get the upper quarks' masses at all.) Well, maybe
this is only the case of the models that represent the Higgs
differently from the present models of Christos. In Christos' models
today, he really derives the exponential form of the masses mainly for
the higgsinos.
It's not yet quite clear to me how the Kahler moduli and the D-brane
positions are really stabilized in these models.
Some advocates of the anthropic flux vacua can argue that they are better
in solving the cosmological constant problem because these N=1 models give
you a wrong C.C. Well, I would buy Christos' approach to isolate the
C.C. problem - a very low energy problem, related to NS-NS tadpoles etc.
in his model - from the rest of particle physics. Outside string theory,
the particle physicists study particle physics independently of the
question of the C.C. String theory unifies everything, so we can't really
isolate two questions completely - but on the other hand, there is a class
of many TeV (and higher) questions whose answer should not be biased by
our attempts to understand something at the sub-eV scale.
The intersecting models give a pretty simple and natural description of
particle physics, and I find it unconvincing to replace them with less
natural and less controllable models only for the sake of explaining one
particular very-low-energy dimensionful number, namely the vacuum energy
density. Feel more than free to disagree and respond.
__{_______________________________________________ _____________________________}
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/0412035
It seems that the intersecting braneworlds have become pretty viable. In
this paper, Christos studies type IIA, T^6 / (Z_3 x Z_3) orbifold plus
orientifold models, with D6-branes not being parallel to the O6-planes.
This orbifold structure has so far not been studied in the intersecting
braneworld context, as far as I understand. This type of orbifold fixes
all the complex structure moduli, just by requiring the Z_3 symmetries.
The Z_3 x Z_3 orbifolding is producing a singular Calabi-Yau, which has
N=2 SUSY with type IIA, and the orientifold planes break it to N=1. The
D6-branes are then wrapped in various other directions, and anomaly
cancellation is a constraint.
A model starting with a 9-generation N=1 model can lead to a *pure*
3-generation N=0 standard model at low energies (below the string scale
which is comparable to the GUT scale). The people who hate new physics -
like Peter Woit - should read the previous sentence twice: it is really a
*pure* Standard Model below the string/Planck scale. Moreover, in some
sense, Christos could argue that the model *predicts* three generations
although he seems probably able to construct less simple
higher-generation models, too.
Various conditions expected from the SUSY GUT theories are reproduced
although it is not a SUSY or GUT theory - the squared sin of the Weinberg
angle is 3/8. It's sort of surprising that this fact appears from so many
non-GUT models - it is a much more general fact about such realistic
theories that "explain" the origin of the Standard Model. alpha2 equals
alpha3 quite naturally, but the real issue is how the hypercharge is
normalized, and it often works like in GUT. For another example of the
features that his models satisfy, Christos argues that some of these
models satisfy the assumption of split supersymmetry.
He can also define models that give you pure Pati-Salam models, pure GUTs
(SU(5) and flipped SU(5)), and so forth. In all these intersecting
braneworlds, the right-handed neutrino is necessary for anomaly
cancellation, and the nature of the Higgs is a bit confusing.
It's not a good idea to copy the paper here. Instead, we should initiate a
discussion. I personally see two main reasons why these models look more
attractive than the flux vacua:
1. They avoid the religion of the uncalculable vast landscape
of nonlinear \sigma models, that naturally leads many to believe the
anthropic feelings. The "number" of the intersecting brane models
is sort of "nicely countable". Physics behind them is a nice theory of
free fields on the worldsheet, which seems perfectly sufficient to
generate life. I don't promote simplicity for the sake of itself,
but especially because the existence and properties of these models
are easier to be verified. The flat space - coming from T^6 - sort of
sounds more naturally to me than curved Calabi-Yaus with huge
curvature, especially because we know that the curvature in the large
4 dimensions is so tiny.
2. They have a natural explanation for the exponential hierarchy of the
fermion masses. (Even though Christos comments that there may be
general problems to get the upper quarks' masses at all.) Well, maybe
this is only the case of the models that represent the Higgs
differently from the present models of Christos. In Christos' models
today, he really derives the exponential form of the masses mainly for
the higgsinos.
It's not yet quite clear to me how the Kahler moduli and the D-brane
positions are really stabilized in these models.
Some advocates of the anthropic flux vacua can argue that they are better
in solving the cosmological constant problem because these N=1 models give
you a wrong C.C. Well, I would buy Christos' approach to isolate the
C.C. problem - a very low energy problem, related to NS-NS tadpoles etc.
in his model - from the rest of particle physics. Outside string theory,
the particle physicists study particle physics independently of the
question of the C.C. String theory unifies everything, so we can't really
isolate two questions completely - but on the other hand, there is a class
of many TeV (and higher) questions whose answer should not be biased by
our attempts to understand something at the sub-eV scale.
The intersecting models give a pretty simple and natural description of
particle physics, and I find it unconvincing to replace them with less
natural and less controllable models only for the sake of explaining one
particular very-low-energy dimensionful number, namely the vacuum energy
density. Feel more than free to disagree and respond.
__{_______________________________________________ _____________________________}
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/
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^