835 research outputs found

### Minimal Gaugomaly Mediation

Mixed anomaly and gauge mediation ("gaugomaly'' mediation) gives a natural
solution to the SUSY flavor problem with a conventional LSP dark matter
candidate. We present a minimal version of gaugomaly mediation where the
messenger masses arise directly from anomaly mediation, automatically
generating a messenger scale of order 50 TeV. We also describe a simple
relaxation mechanism that gives rise to realistic mu and B mu terms. B is
naturally dominated by the anomaly-mediated contribution from top loops, so the
mu/B mu sector only depends on a single new parameter. In the minimal version
of this scenario the full SUSY spectrum is determined by two continuous
parameters (the anomaly- and gauge-mediated SUSY breaking masses) and one
discrete parameter (the number of messengers). We show that these simple models
can give realistic spectra with viable dark matter.Comment: 18 pages, 4 figures; v2: corrected example generating non-holomorphic
Kahler term

### Brane world models need low string scale

Models with large extra dimensions offer the possibility of the Planck scale being of order the electroweak scale, thus alleviating the gauge hierarchy problem. We show that these models suffer from a breakdown of unitarity at around three quarters of the low effective Planck scale. An obvious candidate to fix the unitarity problem is string theory. We therefore argue that it is necessary for the string scale to appear below the effective Planck scale and that the first signature of such models would be string resonances. We further translate experimental bounds on the string scale into bounds on the effective Planck scale

### A Comparison of Supersymmetry Breaking and Mediation Mechanisms

We give a unified treatment of different models of supersymmetry breaking and
mediation from a four dimensional effective field theory standpoint. In
particular a comparison between GMSB and various gravity mediated versions of
SUSY breaking shows that, once the former is embedded within a SUGRA framework,
there is no particular advantage to that mechanism from the point of view of
FCNC suppression. We point out the difficulties of all these scenarios - in
particular the cosmological modulus problem. We end with a discussion of
possible string theory realizations.Comment: Added clarifications and references, 20 page

### Self-organised localisation

Abstract
We describe a new phenomenon in quantum cosmology: self-organised localisation. When the fundamental parameters of a theory are functions of a scalar field subject to large fluctuations during inflation, quantum phase transitions can act as dynamical attractors. As a result, the theory parameters are probabilistically localised around the critical value and the Universe finds itself at the edge of a phase transition. We illustrate how self-organised localisation could account for the observed near-criticality of the Higgs self-coupling, the naturalness of the Higgs mass, or the smallness of the cosmological constant.</jats:p

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### Self-organised localisation

Abstract
We describe a new phenomenon in quantum cosmology: self-organised localisation. When the fundamental parameters of a theory are functions of a scalar field subject to large fluctuations during inflation, quantum phase transitions can act as dynamical attractors. As a result, the theory parameters are probabilistically localised around the critical value and the Universe finds itself at the edge of a phase transition. We illustrate how self-organised localisation could account for the observed near-criticality of the Higgs self-coupling, the naturalness of the Higgs mass, or the smallness of the cosmological constant.</jats:p

### The Minimal Solution to the mu/B_mu Problem in Gauge Mediation

We provide a minimal solution to the mu/B_mu problem in the gauge mediated
supersymmetry breaking by introducing a Standard Model singlet filed S with a
mass around the messenger scale which couples to the Higgs and messenger
fields. This singlet is nearly supersymmetric and acquires a relatively small
Vacuum Expectation Value (VEV) from its radiatively generated tadpole term.
Consequently, both mu and B_mu parameters receive the tree-level and one-loop
contributions, which are comparable due to the small S VEV. Because there
exists a proper cancellation in such two kinds of contributions to B_mu, we can
have a viable Higgs sector for electroweak symmetry breaking.Comment: 15 pages, 2 figures, version published on JHE

### Direct CP violation in charm and flavor mixing beyond the SM

We analyze possible interpretations of the recent LHCb evidence for CP
violation in D meson decays in terms of physics beyond the Standard Model. On
general grounds, models in which the primary source of flavor violation is
linked to the breaking of chiral symmetry (left-right flavor mixing) are
natural candidates to explain this effect, via enhanced chromomagnetic
operators. In the case of supersymmetric models, we identify two motivated
scenarios: disoriented A-terms and split families. These structures predict
other non-standard signals, such as nuclear EDMs close to their present bounds
and, possibly, tiny but visible deviations in K and B physics, or even sizable
flavor-violating processes involving the top quark or the stops. Some of these
connections, especially the one with nuclear EDMs, hold beyond supersymmetry,
as illustrated with the help of prototype non-supersymmetric models.Comment: 30 pages, 6 figure

### Lopsided gauge mediation

It has been recently pointed out that the unavoidable tuning among supersymmetric parameters required to raise the Higgs boson mass beyond its experimental limit opens up new avenues for dealing with the so called mu-B(mu) problem of gauge mediation. In fact, it allows for accommodating, with no further parameter tuning, large values of B(mu) and of the other Higgs-sector soft masses, as predicted in models where both mu and B(mu) are generated at one-loop order. This class of models, called Lopsided Gauge Mediation, offers an interesting alternative to conventional gauge mediation and is characterized by a strikingly different phenomenology, with light higgsinos, very large Higgs pseudoscalar mass, and moderately light sleptons. We discuss general parametric relations involving the fine-tuning of the model and various observables such as the chargino mass and the value of tan beta. We build an explicit model and we study the constraints coming from LEP and Tevatron. We show that in spite of new interactions between the Higgs and the messenger super fields, the theory can remain perturbative up to very large scales, thus retaining gauge coupling unification

### When Anomaly Mediation is UV Sensitive

Despite its successes---such as solving the supersymmetric flavor
problem---anomaly mediated supersymmetry breaking is untenable because of its
prediction of tachyonic sleptons. An appealing solution to this problem was
proposed by Pomarol and Rattazzi where a threshold controlled by a light field
deflects the anomaly mediated supersymmetry breaking trajectory, thus evading
tachyonic sleptons. In this paper we examine an alternate class of deflection
models where the non-supersymmetric threshold is accompanied by a heavy,
instead of light, singlet. The low energy form of this model is the so-called
extended anomaly mediation proposed by Nelson and Weiner, but with potential
for a much higher deflection threshold. The existence of this high deflection
threshold implies that the space of anomaly mediated supersymmetry breaking
deflecting models is larger than previously thought.Comment: 14 pages, 1 figure (version to appear in JHEP

### Higgs mass and vacuum stability in the Standard Model at NNLO

We present the first complete next-to-next-to-leading order analysis of the
Standard Model Higgs potential. We computed the two-loop QCD and Yukawa
corrections to the relation between the Higgs quartic coupling (lambda) and the
Higgs mass (Mh), reducing the theoretical uncertainty in the determination of
the critical value of Mh for vacuum stability to 1 GeV. While lambda at the
Planck scale is remarkably close to zero, absolute stability of the Higgs
potential is excluded at 98% C.L. for Mh < 126 GeV. Possible consequences of
the near vanishing of lambda at the Planck scale, including speculations about
the role of the Higgs field during inflation, are discussed.Comment: 35 pages, 8 figures. Final published version, misprints fixed,
figures update

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