918 research outputs found
Supernova 1987A Constraints on Sub-GeV Dark Sectors, Millicharged Particles, the QCD Axion, and an Axion-like Particle
We consider the constraints from Supernova 1987A on particles with small
couplings to the Standard Model. We discuss a model with a fermion coupled to a
dark photon, with various mass relations in the dark sector; millicharged
particles; dark-sector fermions with inelastic transitions; the hadronic QCD
axion; and an axion-like particle that couples to Standard Model fermions with
couplings proportional to their mass. In the fermion cases, we develop a new
diagnostic for assessing when such a particle is trapped at large mixing
angles. Our bounds for a fermion coupled to a dark photon constrain small
couplings and masses <200 MeV, and do not decouple for low fermion masses. They
exclude parameter space that is otherwise unconstrained by existing
accelerator-based and direct-detection searches. In addition, our bounds are
complementary to proposed laboratory searches for sub-GeV dark matter, and do
not constrain several "thermal" benchmark-model targets. For a millicharged
particle, we exclude charges between 10^(-9) to a few times 10^(-6) in units of
the electron charge; this excludes parameter space to higher millicharges and
masses than previous bounds. For the QCD axion and an axion-like particle, we
apply several updated nuclear physics calculations and include the energy
dependence of the optical depth to accurately account for energy loss at large
couplings. We rule out a hadronic axion of mass between 0.1 and a few hundred
eV, or equivalently bound the PQ scale between a few times 10^4 and 10^8 GeV,
closing the hadronic axion window. For an axion-like particle, our bounds
disfavor decay constants between a few times 10^5 GeV up to a few times 10^8
GeV. In all cases, our bounds differ from previous work by more than an order
of magnitude across the entire parameter space. We also provide estimated
systematic errors due to the uncertainties of the progenitor.Comment: 30 pages + appendices and references, 13 figures. v2: Replaced with
version accepted by JHE
R-symmetry and Supersymmetry Breaking at Finite Temperature
We analyze the spontaneous symmetry breaking at finite temperature
for the simple O'Raifeartaigh-type model introduced in [1] in connection with
spontaneous supersymmetry breaking. We calculate the finite temperature
effective potential (free energy) to one loop order and study the thermal
evolution of the model. We find that the R-symmetry breaking occurs through a
second order phase transition. Its associated meta-stable supersymmetry
breaking vacuum is thermodynamically favored at high temperatures and the model
remains trapped in this state by a potential barrier, as the temperature lowers
all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in
JHE
New Fixed-Target Experiments to Search for Dark Gauge Forces
Fixed-target experiments are ideally suited for discovering new MeV-GeV mass
U(1) gauge bosons through their kinetic mixing with the photon. In this paper,
we identify the production and decay properties of new light gauge bosons that
dictate fixed-target search strategies. We summarize existing limits and
suggest five new experimental approaches that we anticipate can cover most of
the natural parameter space, using currently operating GeV-energy beams and
well-established detection methods. Such experiments are particularly timely in
light of recent terrestrial and astrophysical anomalies (PAMELA, FERMI,
DAMA/LIBRA, etc.) consistent with dark matter charged under a new gauge force.Comment: 14 pages + 6 page appendix and refs, 11 figure
Two Loop R-Symmetry Breaking
We analyze two loop quantum corrections for pseudomoduli in O'Raifeartaigh
like models. We argue that R-symmetry can be spontaneously broken at two loop
in non supersymmetric vacua. We provide a basic example with this property. We
discuss on phenomenological applications.Comment: 13 pages, 5 figures, JHEP3.cls, reference adde
Notes on SUSY and R-Symmetry Breaking in Wess-Zumino Models
We study aspects of Wess-Zumino models related to SUSY and R-symmetry
breaking at tree-level. We present a recipe for constructing a wide class of
tree-level SUSY and R-breaking models. We also deduce a general property shared
by all tree-level SUSY breaking models that has broad application to model
building. In particular, it explains why many models of direct gauge mediation
have anomalously light gauginos (even if the R-symmetry is broken spontaneously
by an order one amount). This suggests new approaches to dynamical SUSY
breaking which can generate large enough gaugino masses.Comment: 23 pages. v2: references added, minor changes. v3: comment on
non-renormalizable case adde
R-symmetric Gauge Mediation and the MRSSM
This is an invited summary of a seminar talk given at various institutions in
the United States and Canada. After a brief introduction, a review of the
minimal R-symmetric supersymmetric standard model is given, and the benefits to
the flavor sector are discussed. R-symmetric gauge mediation is an attempt to
realize this model using metastable supersymmetry breaking techniques. Sample
low energy spectra are presented and tuning is discussed. Various other
phenomenological results are summarized.Comment: 14 pages, invited Brief Review, submitted to Modern Physics Letters
A; v2: replaced Figure 1, updated acknowledgments, fixed typo
A Hybrid Higgs
We construct composite Higgs models admitting a weakly coupled Seiberg dual
description. We focus on the possibility that only the up-type Higgs is an
elementary field, while the down-type Higgs arises as a composite hadron. The
model, based on a confining SQCD theory, breaks supersymmetry and electroweak
symmetry dynamically and calculably. This simultaneously solves the \mu/B_\mu
problem and explains the smallness of the bottom and tau masses compared to the
top mass. The proposal is then applied to a class of models where the same
confining dynamics is used to generate the Standard Model flavor hierarchy by
quark and lepton compositeness. This provides a unified framework for flavor,
supersymmetry breaking and electroweak physics. The weakly coupled dual is used
to explicitly compute the MSSM parameters in terms of a few microscopic
couplings, giving interesting relations between the electroweak and soft
parameters. The RG evolution down to the TeV scale is obtained and salient
phenomenological predictions of this class of "single-sector" models are
discussed.Comment: 56 pages, 7 figures, v2: discussion on FCNCs and references added,
v3: JHEP versio
Dark Matter and Pseudo-flat Directions in Weakly Coupled SUSY Breaking Sectors
We consider candidates for dark matter in models of gauge mediated
supersymmetry breaking, in which the supersymmetry breaking sector is weakly
coupled and calculable. Such models typically contain classically flat
directions, that receive one-loop masses of a few TeV. These pseudo-flat
directions provide a new mechanism to account for the cold dark matter relic
abundance. We discuss also the possibility of heavy gravitino dark matter in
such models.Comment: 16 pages, 2 figures. v2: comments, refs adde
Decays of metastable vacua in SQCD
The decay rates of metastable SQCD vacua in ISS-type models, both towards
supersymmetric vacua as well as towards other nonsupersymmetric configurations
arising in theories with elementary spectators, are estimated numerically in
the semiclassical approximation by computing the corresponding multifield
bounce configurations. The scaling of the bounce action with respect to the
most relevant dimensionless couplings and ratios of scales is analyzed. In the
case of the decays towards the susy vacua generated by nonperturbative effects,
the results confirm previous analytical estimations of this scaling, obtained
by assuming a triangular potential barrier. The decay rates towards susy vacua
generated by R-symmetry breaking interactions turn out to be more than
sufficiently suppressed for the phenomenologically relevant parameter range,
and their behavior in this regime differs from analytic estimations valid for
parametrically small scale ratios. It is also shown that in models with
spectator fields, even though the decays towards vacua involving nonzero
spectator VEVs don't have a strong parametric dependence on the scale ratios,
the ISS vacuum can still be made long-lived in the presence of R-symmetry
breaking interactions.Comment: 22 pages, 7 figure
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