512 research outputs found
Solitonic supersymmetry restoration
Q-balls are a possible feature of any model with a conserved, global U(1)
symmetry and no massless, charged scalars. It is shown that for a broad class
of models of metastable supersymmetry breaking they are extremely influential
on the vacuum lifetime and make seemingly viable vacua catastrophically short
lived. A net charge asymmetry is not required as there is often a significant
range of parameter space where statistical fluctuations alone are sufficient.
This effect is examined for two supersymmetry breaking scenarios. It is found
that models of minimal gauge mediation (which necessarily have a messenger
number U(1)) undergo a rapid, supersymmetry restoring phase transition unless
the messenger mass is greater than 10^8 GeV. Similarly the ISS model, in the
context of direct mediation, quickly decays unless the perturbative
superpotential coupling is greater than the Standard Model gauge couplings.Comment: 17 pages, 3 figures, minor comments added, accepted for publication
in JHE
A smoother end to the dark ages
Independent lines of evidence suggest that the first stars, which ended the
cosmic dark ages, came in pairs, rather than singly. This could change the
prevailing view that the early Universe had a Swiss-cheese-like appearance.Comment: Nature News and Views, April 7, 201
Tree Level Metastability and Gauge Mediation in Baryon Deformed SQCD
We investigate supersymmetric QCD with gauge group SU(2) and a baryon
deformation to the superpotential. The existence of an uplifted vacuum at the
origin with tree level metastability is demonstrated. When this model is
implemented in a direct gauge mediation scenario we therefore find gaugino
masses which are comparable to sfermion masses and parameterised by an
effective number of messengers 1/8. All deformations are well motivated by
appealing to the electric theory and an R-symmetry. This R-symmetry is
explicitly broken by the same term responsible for supersymmetry breaking.
Moreover, the model does not suffer from the Landau pole problem and we find
that it can be described in terms of just two scales: the weak scale and a high
scale like the Planck or GUT scale. The model can be tested by searching for
new particles at the TeV scale charged under the visible sector gauge group.Comment: 17 pages, 7 figures, updated reference
The signature of the first stars in atomic hydrogen at redshift 20
Dark and baryonic matter moved at different velocities in the early Universe,
which strongly suppressed star formation in some regions. This was estimated to
imprint a large-scale fluctuation signal of about 2 mK in the 21-cm spectral
line of atomic hydrogen associated with stars at a redshift of 20, although
this estimate ignored the critical contribution of gas heating due to X-rays
and major enhancements of the suppression. A large velocity difference reduces
the abundance of halos and requires the first stars to form in halos of about a
million solar masses, substantially greater than previously expected. Here we
report a simulation of the distribution of the first stars at z=20 (cosmic age
of ~180 Myr), incorporating all these ingredients within a 400 Mpc box. We find
that the 21-cm signature of these stars is an enhanced (10 mK) fluctuation
signal on the 100-Mpc scale, characterized by a flat power spectrum with
prominent baryon acoustic oscillations. The required sensitivity to see this
signal is achievable with an integration time of a thousand hours with an
instrument like the Murchison Wide-field Array or the Low Frequency Array but
designed to operate in the range of 50-100 MHz.Comment: 27 pages, 5 figures, close (but not exact) match to accepted version.
Basic results unchanged from first submitted version, but justification
strengthened, title and abstract modified, and substantial Supplementary
Material added. Originally first submitted for publication on Oct. 12, 201
Condensate cosmology in O'Raifeartaigh models
Flat directions charged under an R-symmetry are a generic feature of
O'Raifeartaigh models. Non-topological solitons associated with this symmetry,
R-balls, are likely to form through the fragmentation of a condensate, itself
created by soft terms induced during inflation. In gravity mediated SUSY
breaking R-balls decay to gravitinos, reheating the universe. For gauge
mediation R-balls can provide a good dark matter candidate. Alternatively they
can decay, either reheating or cooling the universe. Conserved R-symmetry
permits decay to gravitinos or gauginos, whereas spontaneously broken
R-symmetry results in decay to visible sector gauge bosons.Comment: 29 pages, 5 figures. Comments and references added, accepted for
publication in JHE
Intersecting Flavor Branes
We consider an instance of the AdS/CFT duality where the bulk theory contains
an open string tachyon, and study the instability from the viewpoint of the
boundary field theory. We focus on the specific example of the AdS_5 X S^5
background with two probe D7 branes intersecting at general angles. For generic
angles supersymmetry is completely broken and there is an open string tachyon
between the branes. The field theory action for this system is obtained by
coupling to N =4 super Yang-Mills two N =2 hyper multiplets in the fundamental
representation of the SU(N) gauge group, but with different choices of
embedding of the two N=2 subalgebras into N=4. On the field theory side we find
a one-loop Coleman-Weinberg instability in the effective potential for the
fundamental scalars. We identify a mesonic operator as the dual of the open
string tachyon. By AdS/CFT, we predict the tachyon mass for small 't Hooft
coupling (large bulk curvature) and confirm that it violates the AdS stability
bound.Comment: 36 page
Viability of MSSM scenarios at very large tan(beta)
We investigate the MSSM with very large tan(beta) > 50, where the fermion
masses are strongly affected by loop-induced couplings to the "wrong" Higgs,
imposing perturbative Yukawa couplings and constraints from flavour physics.
Performing a low-energy scan of the MSSM with flavour-blind soft terms, we find
that the branching ratio of B->tau nu and the anomalous magnetic moment of the
muon are the strongest constraints at very large tan(beta) and identify the
viable regions in parameter space. Furthermore we determine the scale at which
the perturbativity of the Yukawa sector breaks down, depending on the
low-energy MSSM parameters. Next, we analyse the very large tan(beta) regime of
General Gauge Mediation (GGM) with a low mediation scale. We investigate the
requirements on the parameter space and discuss the implied flavour
phenomenology. We point out that the possibility of a vanishing Bmu term at a
mediation scale M = 100 TeV is challenged by the experimental data on B->tau nu
and the anomalous magnetic moment of the muon.Comment: 29 pages, 7 figures. v2: discussion in sections 1 and 4 expanded,
conclusions unchanged. Matches version published in JHE
The Schrdinger-Poisson equations as the large-N limit of the Newtonian N-body system: applications to the large scale dark matter dynamics
In this paper it is argued how the dynamics of the classical Newtonian N-body
system can be described in terms of the Schrdinger-Poisson equations
in the large limit. This result is based on the stochastic quantization
introduced by Nelson, and on the Calogero conjecture. According to the Calogero
conjecture, the emerging effective Planck constant is computed in terms of the
parameters of the N-body system as , where is the gravitational constant, and are the
number and the mass of the bodies, and is their average density. The
relevance of this result in the context of large scale structure formation is
discussed. In particular, this finding gives a further argument in support of
the validity of the Schrdinger method as numerical double of the
N-body simulations of dark matter dynamics at large cosmological scales.Comment: Accepted for publication in the Euro. Phys. J.
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