12,438 research outputs found
The Inflaton as a MSSM Higgs and Open String Modulus Monodromy Inflation
It has been recently pointed out that the polarization BICEP2 results are
consistent with the identification of an inflaton mass m \simeq 10^{13} GeV
with the SUSY breaking scale in an MSSM with a fine-tuned SM Higgs. This
identification leads to a Higgs mass m_h \simeq 126 GeV, consistent with LHC
measurements. Here we propose that this naturally suggests to identify the
inflaton with the heavy MSSM Higgs system. The fact that the extrapolated Higgs
coupling lambda_{SM}\simeq 0 at scales below the Planck scale suggests the
Higgs degrees of freedom could be associated to a Wilson line or D-brane
position modulus in string theory. The Higgs system then has a shift symmetry
and an N=2 structure which guarantees that its potential has an approximate
quadratic chaotic inflation form. These moduli in string compactifications,
being compact, allow for a trans-Planckian inflaton field range analogous to a
version of monodromy inflation.Comment: 6 pages. Misprints corrected, references adde
Minkowski 3-forms, Flux String Vacua, Axion Stability and Naturalness
We discuss the role of Minkowski 3-forms in flux string vacua. In these vacua
all internal closed string fluxes are in one to one correspondence with
quantized Minkowski 4-forms. By performing a dimensional reduction of the
Type II supergravity actions we find that the 4-forms act as auxiliary
fields of the Kahler and complex structure moduli in the effective action. We
show that all the RR and NS axion dependence of the flux scalar potential
appears through the said 4-forms. Gauge invariance of these forms then severely
restricts the structure of the axion scalar potentials. Combined with duality
symmetries it suggests that all perturbative corrections to the leading axion
scalar potential should appear as an expansion in powers of itself.
These facts could have an important effect e.g. on the inflaton models based on
F-term axion monodromy. We also suggest that the involved multi-branched
structure of string vacua provides for a new way to maintain interacting scalar
masses stable against perturbative corrections.Comment: 39 pages. Typos corrected and added reference
Flux-induced Soft Terms on Type IIB/F-theory Matter Curves and Hypercharge Dependent Scalar Masses
Closed string fluxes induce generically SUSY-breaking soft terms on
supersymmetric type IIB orientifold compactifications with D3/D7 branes. This
was studied in the past by inserting those fluxes on the DBI+CS actions for
adjoint D3/D7 fields, where D7-branes had no magnetic fluxes. In the present
work we generalise those computations to the phenomenologically more relevant
case of chiral bi-fundamental fields laying at 7-brane intersections and
F-theory local matter curves. We also include the effect of 7-brane magnetic
flux as well as more general closed string backgrounds, including the effect of
distant (anti-)D3-branes. We discuss several applications of our results. We
find that squark/slepton masses become in general flux-dependent in F-theory
GUT's. Hypercharge-dependent non-universal scalar masses with a characteristic
sfermion hierarchy m_E^2 < m_L^2 < m_Q^2 < m_D^2 < m_U^2 are obtained. There
are also flavor-violating soft terms both for matter fields living at
intersecting 7-branes or on D3-branes at singularities. They point at a very
heavy sfermion spectrum to avoid FCNC constraints. We also discuss the possible
microscopic description of the fine-tuning of the EW Higgs boson in
compactifications with a MSSM spectrum.Comment: 67 pages, 2 figures, 2 table
Relaxion Monodromy and the Weak Gravity Conjecture
The recently proposed relaxion models require extremely large trans-Planckian
axion excursions as well as a potential explicitly violating the axion shift
symmetry. The latter property is however inconsistent with the axion
periodicity, which corresponds to a gauged discrete shift symmetry. A way to
make things consistent is to use monodromy, i.e. both the axion and the
potential parameters transform under the discrete shift symmetry. The structure
is better described in terms of a 3-form field coupling to
the SM Higgs through its field strength . The 4-form also couples linearly
to the relaxion, in the Kaloper-Sorbo fashion. The extremely small
relaxion-Higgs coupling arises in a see-saw fashion as , with
being the axion decay constant. We discuss constraints on this type of
constructions from membrane nucleation and the Weak Gravity Conjecture. The
latter requires the existence of membranes, whose too fast nucleation could in
principle drive the theory out of control, unless the cut-off scale is lowered.
This allows to constrain relaxion models on purely theoretical grounds. We also
discuss possible avenues to embed this structure into string theory.Comment: 26 pages + appendices, 3 figures; v3: Corrected bounds on relaxion
parameter spac
Mapping the galaxy NGC 4486 (M87) through its Globular Cluster System
As shown in previous works, globular clusters can be used to trace the
overall structure of the diffuse stellar populations in early type galaxies if
the number of clusters per unit stellar mass depends on metallicity. In this
paper we further test this assumption in the galaxy NGC 4486 (M 87), by
combining several data sources. The results show that globular clusters allow
the mapping of the galaxy in terms of the surface brightness profile,
integrated colour gradient, chemical abundance, and mass to luminosity ratios
up to 1000 arcsec (or 80.4 kpc) from its centre (i.e. some 10 effective radii).
The analysis indicates the presence of a dominant high metallicity bulge
associated with the red globulars, whose ellipticity increases outwards, and of
a more flattened low metallicity halo connected with the blue globulars. The
chemical abundance gradient of the composite stellar population is remarkably
similar to that inferred from X ray observations of hot gas. The
mass-metallicity spectrum of the stellar population can, in principle, be
understood in terms of inhomogeneous enrichment models. In turn, the
distribution of the bluest GCs, and lowest metallicity halo stars, has an
intriguing similarity with that of dark matter, a feature shared with NGC 1399.
Also, in these two galaxies, the number of blue GCs per dark mass unit is
identical within the errors, \approx 1.0(\pm0.3) \times 10^{-9} . The total
stellar mass derived for NGC 4486 is 6.8(\pm1.1) \times 10^{11} M\odot with a
baryonic mass fraction fb = 0.08(\pm 0.01).Comment: 18 pages, 23 figure
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