751 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

### Loop Quantum Gravity Corrections and Cosmic Ray Decays

Loop quantum gravity effective theories are reviewed in the context of the
observed GZK limit anomaly and related processes. This is accomplished through
a kinematical analysis of the modified threshold conditions for the involved
decay reactions, arising from the theory. Specially interesting is the
possibility of an helicity dependant violation of the limit, whose primary
effect would be the observation of favoured helicity states for highly
energetic particles.Comment: Revtex, 19 pages. Additional reference

### 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 $\Delta \phi \leq \Delta \sim \mathcal
O(1)$ (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 $V$ is positive, its slope must be bounded from below, and
suggests $|\nabla V| / V \geq c \sim \mathcal O(1)$. 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 $\Omega$ of the multi-field
trajectory). We derive a universal lower bound on $\Omega$ (relative to the
Hubble parameter $H$) as a function of $\Delta, c$ and the number of efolds
$N_e$, assumed to be at least of order 60. If later studies confirm $c$ and
$\Delta$ to be strictly $\mathcal O(1)$, the bound implies strong turns with
$\Omega / H \geq 3 N_e \sim 180$. 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

### On the integration of fields and quanta in time dependent backgrounds

Field theories with global continuous symmetries may admit configurations in
which time translation invariance is broken by the movement of homogeneous
background fields evolving along the flat directions implied by the symmetries.
In this context, the field fluctuations along the broken symmetry are well
parametrized by a Goldstone boson field that may non-trivially interact with
other fields present in the theory. These interactions violate Lorentz
invariance as a result of the broken time translation invariance of the
background, producing a mixing between the field content and the particle
spectrum of the theory. In this article we study the effects of such
interactions on the low energy dynamics of the Goldstone boson quanta, paying
special attention to the role of the particle spectrum of the theory. By
studying the particular case of a canonical two-field model with a mexican-hat
potential, we analyze the derivation of the low energy effective field theory
for the Goldstone boson, and discuss in detail the distinction between
integrating fields v/s integrating quanta, to finally conclude that they are
equivalent. In addition, we discuss the implications of our analysis for the
study of systems where time translation invariance is broken, such as cosmic
inflation and time crystals.Comment: 38 pages, 1 figur

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