180 research outputs found

### Dark Matter in Gauge Mediation from Emergent Supersymmetry

We investigated the viability of neutralino dark matter in the gauge
mediation from emergent supersymmetry proposal. In this proposal, supersymmetry
is broken at Planck scale and consequently, the gravitino is superheavy and
completely decouples from the low energy theory. Squarks and sleptons obtain
their soft masses dominantly through gauge mediation with other mechanisms
highly suppressed. The lightest supersymmetric partner, in contrast to
traditional gauge mediation, is a neutralino which is also a dark matter
candidate. By explicit calculation of the low energy spectra, the parameter
space was constrained using the WMAP observed relic density of dark matter,
LEP2 Higgs mass bounds, collider bounds on supersymmetric partners and exotic
B-meson decays. We found that the model has intriguing hybrid features such as
a nearly gauge-mediated spectrum (the exception being the superheavy gravitino)
but with a dominant mSUGRA-like bino-stau coannihilation channel and at large
$\tan \beta$, A-resonance-like annihilation.Comment: 14 pages, 4 figure

### Baryon masses at second order in large-$N$ chiral perturbation theory

We consider flavor breaking in the the octet and decuplet baryon masses at
second order in large-$N$ chiral perturbation theory, where $N$ is the number
of QCD colors. We assume that $1/N \sim 1/N_F \sim m_s / \Lambda \gg
m_{u,d}/\Lambda, \alpha_{EM}$, where $N_F$ is the number of light quark
flavors, and $m_{u,d,s} / \Lambda$ are the parameters controlling $SU(N_F)$
flavor breaking in chiral perturbation theory. We consistently include
non-analytic contributions to the baryon masses at orders $m_q^{3/2}$, $m_q^2
\ln m_q$, and $(m_q \ln m_q) / N$. The $m_q^{3/2}$ corrections are small for
the relations that follow from $SU(N_F)$ symmetry alone, but the corrections to
the large-$N$ relations are large and have the wrong sign. Chiral
power-counting and large-$N$ consistency allow a 2-loop contribution at order
$m_q^2 \ln m_q$, and a non-trivial explicit calculation is required to show
that this contribution vanishes. At second order in the expansion, there are
eight relations that are non-trivial consequences of the $1/N$ expansion, all
of which are well satisfied within the experimental errors. The average
deviation at this order is 7 \MeV for the \De I = 0 mass differences and
0.35 \MeV for the \De I \ne 0 mass differences, consistent with the
expectation that the error is of order $1/N^2 \sim 10\%$.Comment: 19 pages, 2 uuencoded ps figs, uses revte

### Boundary Terms and Junction Conditions for the DGP Pi-Lagrangian and Galileon

In the decoupling limit of DGP, Pi describes the brane-bending degree of
freedom. It obeys second order equations of motion, yet it is governed by a
higher derivative Lagrangian. We show that, analogously to the Einstein-Hilbert
action for GR, the Pi-Lagrangian requires Gibbons-Hawking-York type boundary
terms to render the variational principle well-posed. These terms are important
if there are other boundaries present besides the DGP brane, such as in higher
dimensional cascading DGP models. We derive the necessary boundary terms in two
ways. First, we derive them directly from the brane-localized Pi-Lagrangian by
demanding well-posedness of the action. Second, we calculate them directly from
the bulk, taking into account the Gibbons-Hawking-York terms in the bulk
Einstein-Hilbert action. As an application, we use the new boundary terms to
derive Israel junction conditions for Pi across a sheet-like source. In
addition, we calculate boundary terms and junction conditions for the galileons
which generalize the DGP Pi-lagrangian, showing that the boundary term for the
n-th order galileon is the (n-1)-th order galileon.Comment: 23 pages, 1 figure. Extended the analysis to the general galileon
field. Version to appear in JHE

### Strong Conformal Dynamics at the LHC and on the Lattice

Conformal technicolor is a paradigm for new physics at LHC that may solve the
problems of strong electroweak symmetry breaking for quark masses and precision
electroweak data. We give explicit examples of conformal technicolor theories
based on a QCD-like sector. We suggest a practical method to test the conformal
dynamics of these theories on the lattice.Comment: v2: Generalized discussion of lattice measurement of hadron masses,
references added, minor clarifications v3: references added, minor change

### Effective Action and Holography in 5D Gauge Theories

We apply the holographic method to 5D gauge theories on the warped interval.
Our treatment includes the scalars associated with the fifth gauge field
component, which appear as 4D Goldstone bosons in the holographic effective
action. Applications are considered to two classes of models in which these
scalars play an important role. In the Composite-Higgs (and/or Gauge-Higgs
Unification) scenario, the scalars are interpreted as the Higgs field and we
use the holographic recipe to compute its one-loop potential. In AdS/QCD
models, the scalars are identified with the mesons and we compute
holographically the Chiral Perturbation Theory Lagrangian up to p^4 order. We
also discuss, using the holographic perspective, the effect of including a
Chern-Simons term in the 5D gauge Lagrangian. We show that it makes a
Wess-Zumino-Witten term to appear in the holographic effective action. This is
immediately applied to AdS/QCD, where a Chern-Simons term is needed in order to
mimic the Adler-Bardeen chiral anomaly.Comment: 37 pages; v2, minor changes, one reference added; v3, minor
corrections, version published in JHE

### The Minimal Supersymmetric Fat Higgs Model

We present a calculable supersymmetric theory of a composite ``fat'' Higgs
boson. Electroweak symmetry is broken dynamically through a new gauge
interaction that becomes strong at an intermediate scale. The Higgs mass can
easily be 200-450 GeV along with the superpartner masses, solving the
supersymmetric little hierarchy problem. We explicitly verify that the model is
consistent with precision electroweak data without fine-tuning. Gauge coupling
unification can be maintained despite the inherently strong dynamics involved
in electroweak symmetry breaking. Supersymmetrizing the Standard Model
therefore does not imply a light Higgs mass, contrary to the lore in the
literature. The Higgs sector of the minimal Fat Higgs model has a mass spectrum
that is distinctly different from the Minimal Supersymmetric Standard Model.Comment: 13 pages, 5 figures, REVTe

### Leptogenesis, neutrino masses and gauge unification

Leptogenesis is considered in its natural context where Majorana neutrinos
fit in a gauge unification scheme and therefore couple to some extra gauge
bosons. The masses of some of these gauge bosons are expected to be similar to
those of the heavy Majorana particles, and this can have important consequences
for leptogenesis. In fact, the effect can go both ways. Stricter bounds are
obtained on one hand due to the dilution of the CP-violating effect by new
decay and scattering channels, while, in a re-heating scheme, the presence of
gauge couplings facilitates the re-population of the Majorana states. The
latter effect allows in particular for smaller Dirac couplings.Comment: 11pages, 7 figures. v2: definition of the lepton asymmetry corrected,
small numerical changes for the baryon number, conclusion does not change;
typos corrected and references adde

### The Gaugephobic Higgs

We present a class of models that contains Randall-Sundrum and Higgsless
models as limiting cases. Over a wide range of the parameter space WW
scattering is mainly unitarized by Kaluza-Klein partners of the W and Z, and
the Higgs particle has suppressed couplings to the gauge bosons. Such a
gaugephobic Higgs can be significantly lighter than the 114 GeV LEP bound for a
standard Higgs, or heavier than the theoretical upper bound. These models
predict a suppressed single top production rate and unconventional Higgs
phenomenology at the LHC: the Higgs production rates will be suppressed and the
Higgs branching fractions modified. However, the more difficult the Higgs
search at the LHC is, the easier the search for other light resonances (like
Z', W', t', exotic fermions) will be.Comment: 20 pages, 3 figure

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