11,511 research outputs found
Confining the Electroweak Model to a Brane
We introduce a simple scenario where, by starting with a five-dimensional
SU(3) gauge theory, we end up with several 4-D parallel branes with localized
fermions and gauge fields. Similar to the split fermion scenario, the
confinement of fermions is generated by the nontrivial topological solution of
a SU(3) scalar field. The 4-D fermions are found to be chiral, and to have
interesting properties coming from their 5-D group representation structure.
The gauge fields, on the other hand, are localized by loop corrections taking
place at the branes produced by the fermions. We show that these two confining
mechanisms can be put together to reproduce the basic structure of the
electroweak model for both leptons and quarks. A few important results are:
Gauge and Higgs fields are unified at the 5-D level; and new fields are
predicted: One left-handed neutrino with zero-hypercharge, and one massive
vector field coupling together the new neutrino with other left-handed leptons.
The hierarchy problem is also addressed.Comment: 9 pages, 8 figures; references added; version published in PR
The string swampland constraints require multi-field inflation
An important unsolved problem that affects practically all attempts to
connect string theory to cosmology and phenomenology is how to distinguish
effective field theories belonging to the string landscape from those that are
not consistent with a quantum theory of gravity at high energies (the "string
swampland"). It was recently proposed that potentials of the string landscape
must satisfy at least two conditions, the "swampland criteria", that severely
restrict the types of cosmological dynamics they can sustain. The first
criterion states that the (multi-field) effective field theory description is
only valid over a field displacement (in units where the Planck mass is 1), measured as a distance in the
target space geometry. A second, more recent, criterion asserts that, whenever
the potential is positive, its slope must be bounded from below, and
suggests . A recent analysis
concluded that these two conditions taken together practically rule out
slow-roll models of inflation. In this note we show that the two conditions
rule out inflationary backgrounds that follow geodesic trajectories in field
space, but not those following curved, non-geodesic, trajectories (which are
parametrized by a non-vanishing bending rate of the multi-field
trajectory). We derive a universal lower bound on (relative to the
Hubble parameter ) as a function of and the number of efolds
, assumed to be at least of order 60. If later studies confirm and
to be strictly , the bound implies strong turns with
. Slow-roll inflation in the landscape is not
ruled out, but it is strongly multi-field.Comment: v1: 15 pages; v2: 16 pages, references added, improved discussions,
version accepted for publication in JCA
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