48 research outputs found
Small Numbers from Tunneling Between Brane Throats
Generic classes of string compactifications include ``brane throats''
emanating from the compact dimensions and separated by effective potential
barriers raised by the background gravitational fields. The interaction of
observers inside different throats occurs via tunnelling and is consequently
weak. This provides a new mechanism for generating small numbers in Nature. We
apply it to the hierarchy problem, where supersymmetry breaking near the
unification scale causes TeV sparticle masses inside the standard model throat.
We also design naturally long-lived cold dark matter which decays within a
Hubble time to the approximate conformal matter of a long throat. This may
soften structure formation at galactic scales and raises the possibility that
much of the dark matter of the universe is conformal matter. Finally, the
tunnelling rate shows that the coupling between throats, mediated by bulk
modes, is stronger than a naive application of holography suggests.Comment: 11 pages, 2 figures. Small corrections to match the published versio
The Emperor's Last Clothes?
We are in the middle of a remarkable paradigm shift in particle physics, a
shift of opinion that occurred so slowly that some even try to deny that they
changed their minds at all. It concerns a very basic question: can we expect to
derive the laws of particle physics from a fundamental theory? The Standard
Model of particle physics as well as the 1984 string theory revolution provided
ample food for thought about this. The reason this was ignored for so long can
be traced back to an old fallacy: a misguided idea about our own importance.Comment: 88 pages, Review intended for readers with an education in physics.
Preprint Nr. added, some statements corrected, some references added. A short
version (about 20 pages) was published in Rept. Prog. Phys. 71:072201,2008.
July 2010: Footnote added to correct a remark on nuclear bindin
Weak gravity conjecture constraints on inflation
We consider the gravitational correction to the coupling of the scalar
fields. Weak gravity conjecture says that the gravitational correction to the
running of scalar coupling should be less than the contribution from scalar
fields. For instance, a new scale sets a UV cutoff
on the validity of the effective theory. Furthermore, this
conjecture implies a possible constraint on the inflation model, e.g. the
chaotic inflation model might be in the swampland.Comment: 11 pages, 3 figs; monor corrections; some clarifying remarks added
and the final version for publication in JHE
An Ignoble Approach to Large Field Inflation
We study an inflationary model developed by Kaloper and Sorbo, in which the
inflaton is an axion with a sub-Planckian decay constant, whose potential is
generated by mixing with a topological 4-form field strength. This gives a 4d
construction of "axion monodromy inflation": the axion winds many times over
the course of inflation and draws energy from the 4-form. The classical theory
is equivalent to chaotic inflation with a quadratic inflaton potential. Such
models can produce "high scale" inflation driven by energy densities of the
order of , which produces primordial gravitational waves
potentially accessible to CMB polarization experiments. We analyze the possible
corrections to this scenario from the standpoint of 4d effective field theory,
identifying the physics which potentially suppresses dangerous corrections to
the slow-roll potential. This yields a constraint relation between the axion
decay constant, the inflaton mass, and the 4-form charge. We show how these
models can evade the fundamental constraints which typically make high-scale
inflation difficult to realize. Specifically, the moduli coupling to the
axion-four-form sector must have masses higher than the inflationary Hubble
scale (\la\ 10^{14}\ GeV). There are also constraints from states that become
light due to multiple windings of the axion, as happens in explicit string
theory constructions of this scenario. Further, such models generally have a
quantum-mechanical "tunneling mode" in which the axion jumps between windings,
which must be suppressed. Finally, we outline possible observational
signatures.Comment: 39 pages LaTeX with bibtex, 5 .eps figure
N-flation
The presence of many axion fields in four-dimensional string vacua can lead
to a simple, radiatively stable realization of chaotic inflation.Comment: 16 pages, 0 figures, latex; v2: added refs; v3: more refs, correction
to \S2.
Minimal Gaugomaly Mediation
Mixed anomaly and gauge mediation ("gaugomaly'' mediation) gives a natural
solution to the SUSY flavor problem with a conventional LSP dark matter
candidate. We present a minimal version of gaugomaly mediation where the
messenger masses arise directly from anomaly mediation, automatically
generating a messenger scale of order 50 TeV. We also describe a simple
relaxation mechanism that gives rise to realistic mu and B mu terms. B is
naturally dominated by the anomaly-mediated contribution from top loops, so the
mu/B mu sector only depends on a single new parameter. In the minimal version
of this scenario the full SUSY spectrum is determined by two continuous
parameters (the anomaly- and gauge-mediated SUSY breaking masses) and one
discrete parameter (the number of messengers). We show that these simple models
can give realistic spectra with viable dark matter.Comment: 18 pages, 4 figures; v2: corrected example generating non-holomorphic
Kahler term
Cosmology From Random Multifield Potentials
We consider the statistical properties of vacua and inflationary trajectories
associated with a random multifield potential. Our underlying motivation is the
string landscape, but our calculations apply to general potentials. Using
random matrix theory, we analyze the Hessian matrices associated with the
extrema of this potential. These potentials generically have a vast number of
extrema. If the cross-couplings (off-diagonal terms) are of the same order as
the self-couplings (diagonal terms) we show that essentially all extrema are
saddles, and the number of minima is effectively zero. Avoiding this requires
the same separation of scales needed to ensure that Newton's constant is stable
against radiative corrections in a string landscape. Using the central limit
theorem we find that even if the number of extrema is enormous, the typical
distance between extrema is still substantial -- with challenging implications
for inflationary models that depend on the existence of a complicated path
inside the landscape.Comment: revtex, 3 figures, 10 pages v2 refs adde
Eternal Chaotic Inflation is Prohibited by Weak Gravity Conjecture
We investigate whether the eternal chaotic inflation can be achieved when the
weak gravity conjecture is taken into account. We show that even the assisted
chaotic inflation with potential or can not be
eternal. The effective field theory description for the inflaton field breaks
down before inflation reaches the eternal regime. We also find that the total
number of e-folds is still bounded by the inflationary entropy for the assisted
inflation.Comment: 10 page
Holographic metastability
We show how supersymmetric QCD in a slice of AdS can naturally acquire
metastable vacua. The formulation closely follows that of Intriligator, Seiberg
and Shih (ISS), with an "electric" sector on the UV brane and a "magnetic"
sector on the IR brane. However the 't Hooft anomaly matching that constrains
the Seiberg duality central to ISS is replaced by anomaly inflow and
cancellation, and the source of strong coupling is the CFT to which the theory
couples rather than the gauge groups. The theory contains an anomaly free
R-symmetry that, when broken by UV effects, leads to an O'Raifeartaigh model on
the IR brane. In contrast to ISS, the R-symmetry breaking in the UV can be
maximal, and yet the R-symmetry breaking in the IR theory remains under strict
control: there is no need for retrofitting of small parameters.Comment: 20 pages, 2 figure
Bounds on masses of bulk fields in string compactifications
In string compactification on a manifold X, in addition to the string scale
and the normal scales of low-energy particle physics, there is a Kaluza-Klein
scale 1/R associated with the size of X. We present an argument that generic
string models with low-energy supersymmetry have, after moduli stabilization,
bulk fields with masses which are parametrically lighter than 1/R. We discuss
the implications of these light states for anomaly mediation and gaugino
mediation scenarios.Comment: 15 page