412 research outputs found
Field-theoretic Methods in Strongly-Coupled Models of General Gauge Mediation
An often-exploited feature of the operator product expansion (OPE) is that it
incorporates a splitting of ultraviolet and infrared physics. In this paper we
use this feature of the OPE to perform simple, approximate computations of soft
masses in gauge-mediated supersymmetry breaking. The approximation amounts to
truncating the OPEs for hidden-sector current-current operator products. Our
method yields visible-sector superpartner spectra in terms of vacuum
expectation values of a few hidden-sector IR elementary fields. We manage to
obtain reasonable approximations to soft masses, even when the hidden sector is
strongly coupled. We demonstrate our techniques in several examples, including
a new framework where supersymmetry-breaking arises both from a hidden sector
and dynamically.Comment: 27 pages, 5 figures. Expanded discussion, fixed typos, added
reference
Photon-Dark Photon Conversions in Background Electromagnetic Fields
The mixing of photons with light pseudoscalars in the presence of external
electromagnetic fields has been used extensively to search for
axion-like-particles. A similar effect for dark photon propagating states is
usually not considered due to the Landau-Yang theorem. We point out that mixing
between photon and dark photon propagating states in background electromagnetic
fields can indeed occur, in non-linear QED, through a four-photon vertex by
integrating out the electron box diagram. Starting from the Schwinger
Lagrangian, we derive the equations of motion for dark photons interacting with
the Standard Model photon through gauge kinetic terms. We provide expressions
for the perpendicular and parallel refractive indices in series expansions in
the critical field strength, valid both in the strong and weak background field
limits. We then consider mixing between the photon-dark photon propagating
system in the presence of pure electric and magnetic background fields, and
work out the probability of conversion when the background fields are
homogeneous. We indicate outlines of the calculation in the inhomogeneous case,
and finally express our results in the active-sterile basis, where we find that
the mixing induced by background fields can lead to corrections to the
tree-level mixing in the zero field limit that is usually considered to probe
such systems. Our results may find applications for probing photon-dark photon
conversions in the vicinity of neutron stars and in table-top petawatt laser
experiments.Comment: 1+16 pages, added references, probability of conversion given in
physical basis, conclusions unchange
Constraining Axion-Like-Particles with Hard X-ray Emission from Magnetars
Axion-like particles (ALPs) produced in the core of a magnetar will convert
to photons in the magnetosphere, leading to possible signatures in the hard
X-ray band. We perform a detailed calculation of the ALP-to-photon conversion
probability in the magnetosphere, recasting the coupled differential equations
that describe ALP-photon propagation into a form that is efficient for large
scale numerical scans. We show the dependence of the conversion probability on
the ALP energy, mass, ALP-photon coupling, magnetar radius, surface magnetic
field, and the angle between the magnetic field and direction of propagation.
Along the way, we develop an analytic formalism to perform similar calculations
in more general -state oscillation systems. Assuming ALP emission rates from
the core that are just subdominant to neutrino emission, we calculate the
resulting constraints on the ALP mass versus ALP-photon coupling space, taking
SGR 1806-20 as an example. In particular, we take benchmark values for the
magnetar radius and core temperature, and constrain the ALP parameter space by
the requirement that the luminosity from ALP-to-photon conversion should not
exceed the total observed luminosity from the magnetar. The resulting
constraints are competitive with constraints from helioscope experiments in the
relevant part of ALP parameter space.Comment: 1+20 pages, 5 figures, typos fixe
Anarchy and Neutrino Physics
The neutrino sector of a seesaw-extended Standard Model is investigated under
the anarchy hypothesis. The previously derived probability density functions
for neutrino masses and mixings, which characterize the type I-III seesaw
ensemble of complex random matrices, are used to extract
information on the relevant physical parameters. For and , the
distributions of the light neutrino masses, as well as the mixing angles and
phases, are obtained using numerical integration methods. A systematic
comparison with the much simpler type II seesaw ensemble is also performed to
point out the fundamental differences between the two ensembles. It is found
that the type I-III seesaw ensemble is better suited to accommodate
experimental data. Moreover, the results indicate a strong preference for the
mass splitting associated to normal hierarchy. However, since all permutations
of the singular values are found to be equally probable for a particular mass
splitting, predictions regarding the hierarchy of the mass spectrum remains out
of reach in the framework of anarchy.Comment: 1+22 pages, 8 figures, typos fixed, added referenc
Fixing the Pole in the Pyramid
We revisit the problem of the hidden sector Landau pole in the Pyramid
Scheme. There is a fixed line in the plane of hidden sector gauge coupling and
a Yukawa coupling between the trianon fields. We postulate that the couplings
flow to this line, at a point where the hidden sector gauge coupling is close
to the strong coupling edge of its perturbative regime. Below the masses of the
heavier trianons, the model quickly flows to a confining N_F=N_C=3
supersymmetric gauge theory, as required by phenomenological considerations. We
study possible discrete R-symmetries, which guarantee, among other things, that
the basin of attraction of the fixed line has full co-dimension in the space of
R-allowed couplings. The Yukawa couplings required to get the fixed line
violate the pyrma-baryon symmetries we invoked in previous work to find a dark
matter candidate. Omitting one of them, we have a dark matter candidate, and an
acceptable RG flow down from the unification scale, if the confinement scale of
the hidden sector group is lowered from 5 to 2 TeV.Comment: 14 pages, 3 table
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