75 research outputs found
Brane World Susy Breaking from String/M Theory
String and M-theory realizations of brane world supersymmetry breaking
scenarios are considered in which visible sector Standard Model fields are
confined on a brane, with hidden sector supersymmetry breaking isolated on a
distant brane. In calculable examples with an internal manifold of any volume
the Kahler potential generically contains brane--brane non-derivative contact
interactions coupling the visible and hidden sectors and is not of the no-scale
sequestered form. This leads to non-universal scalar masses and without
additional assumptions about flavor symmetries may in general induce dangerous
sflavor violation even though the Standard Model and supersymmetry branes are
physically separated. Deviations from the sequestered form are dictated by bulk
supersymmetry and can in most cases be understood as arising from exchange of
bulk supergravity fields between branes or warping of the internal geometry.
Unacceptable visible sector tree-level tachyons arise in many models but may be
avoided in certain classes of compactifications. Anomaly mediated and gaugino
mediated contributions to scalar masses are sub-dominant except in special
circumstances such as a flat or AdS pure five--dimensional bulk geometry
without bulk vector multiplets.Comment: Latex, 83 pages, references adde
Abelian D-terms and the superpartner spectrum of anomaly-mediated supersymmetry breaking
We address the tachyonic slepton problem of anomaly mediated supersymmetry
breaking using abelian D-terms. We demonstrate that the most general extra U(1)
symmetry that does not disrupt gauge coupling unification has a large set of
possible charges that solves the problem. It is shown that previous studies in
this direction that added both an extra hypercharge D-term and another D-term
induced by B-L symmetry (or similar) can be mapped into a single D-term of the
general ancillary U(1)_a. The U(1)_a formalism enables identifying the sign of
squark mass corrections which leads to an upper bound of the entire
superpartner spectrum given knowledge of just one superpartner mass.Comment: 10 pages, 2 figures, [v2] reference added, [v3] Eq. (9) corrected,
results unaffected, [v4] version to be published in Phys. Rev. D, expanded
parameter space for figures to match tex
Expectations for LHC from Naturalness: Modified vs. SM Higgs Sector
Common lore has it that naturalness of electroweak breaking in the SM
requires new physics (NP) at Lambda < 2-3 TeV, hopefully within the reach of
LHC. Moreover the Higgs should be light (m_h < 219 GeV) to pass electroweak
precision tests (EWPT). However one should be prepared for "unexpected"
(although admittedly unpleasant) results at LHC, i.e. no NP and/or a heavy
Higgs. We revisit recent attempts to accommodate this by modifying the SM Higgs
sector (using 2-Higgs-doublet models). We find that these models do not improve
the naturalness of the SM, and so they do not change the expectations of
observing NP at LHC. We also stress that a heavy SM Higgs would not be evidence
in favour of a modified Higgs sector, provided certain higher order operators
influence EWPT. On the other hand, we show that NP can escape LHC detection
without a naturalness price, and with the pure SM as the effective theory valid
at LHC energies, simply if the cut-off for top loops is slightly lower than for
Higgs loops.Comment: 37 pages, LaTeX, 13 figure
Anomaly Mediation, Fayet-Iliopoulos D-terms and the Renormalisation Group
We address renormalisation group evolution issues that arise in the Anomaly
Mediated Supersymmetry Breaking scenario when the tachyonic slepton problem is
resolved by Fayet-Iliopoulos term contributions. We present typical sparticle
spectra both for the original formulation of this idea and an alternative using
Fayet-Iliopoulos terms for a U(1) compatible with a straightforward GUT
embedding.Comment: 20 pages, 2 figure
Phenomenology of Mixed Modulus-Anomaly Mediation in Fluxed String Compactifications and Brane Models
In some string compactifications, for instance the recently proposed KKLT
set-up, light moduli are stabilized by nonperturbative effects at
supersymmetric AdS vacuum which is lifted to a dS vacuum by supersymmetry
breaking uplifting potential. In such models, soft supersymmetry breaking terms
are determined by a specific mixed modulus-anomaly mediation in which the two
mediations typically give comparable contributions to soft parameters. Similar
pattern of soft terms can arise also in brane models to stabilize the radion by
nonperturbative effects. We examine some phenomenological consequences of this
mixed modulus-anomaly mediation, including the pattern of low energy sparticle
spectrum and the possibility of electroweak symmetry breaking. It is noted that
adding the anomaly-mediated contributions at amounts to replacing the
messenger scale of the modulus mediation by a mirage messenger scale
where
for denoting the
modulus-mediated contribution to the gaugino mass at . The minimal
KKLT set-up predicts . As a consequence, for ,
the model can lead to a highly distinctive pattern of sparticle masses at TeV
scale, particularly when .Comment: 20 pages, 15 figures, some notations are changed, typos are corrected
and discussions on the CP phase from and B are adde
Electroweak Symmetry Breaking via UV Insensitive Anomaly Mediation
Anomaly mediation solves the supersymmetric flavor and CP problems. This is
because the superconformal anomaly dictates that supersymmetry breaking is
transmitted through nearly flavor-blind infrared physics that is highly
predictive and UV insensitive. Slepton mass squareds, however, are predicted to
be negative. This can be solved by adding D-terms for U(1)_Y and U(1)_{B-L}
while retaining the UV insensitivity. In this paper we consider electroweak
symmetry breaking via UV insensitive anomaly mediation in several models. For
the MSSM we find a stable vacuum when tanbeta < 1, but in this region the top
Yukawa coupling blows up only slightly above the supersymmetry breaking scale.
For the NMSSM, we find a stable electroweak breaking vacuum but with a chargino
that is too light. Replacing the cubic singlet term in the NMSSM superpotential
with a term linear in the singlet we find a stable vacuum and viable spectrum.
Most of the parameter region with correct vacua requires a large superpotential
coupling, precisely what is expected in the ``Fat Higgs'' model in which the
superpotential is generated dynamically. We have therefore found the first
viable UV complete, UV insensitive supersymmetry breaking model that solves the
flavor and CP problems automatically: the Fat Higgs model with UV insensitive
anomaly mediation. Moreover, the cosmological gravitino problem is naturally
solved, opening up the possibility of realistic thermal leptogenesis.Comment: 27 pages, 3 figures, 1 tabl
R-mediation of Dynamical Supersymmetry Breaking
We propose a simple scenario of the dynamical supersymmetry breaking in four
dimensional supergravity theories. The supersymmetry breaking sector is assumed
to be completely separated as a sequestered sector from the visible sector,
except for the communication by the gravity and U(1)_R gauge interactions, and
the supersymmetry breaking is mediated by the superconformal anomaly and U(1)_R
gauge interaction. Supersymmetry is dynamically broken by the interplay between
the non-perturbative effect of the gauge interaction and Fayet-Iliopoulos
D-term of U(1)_R which necessarily exists in supergravity theories with gauged
U(1)_R symmetry. We construct an explicit model which gives phenomenologically
acceptable mass spectrum of superpartners with vanishing (or very small)
cosmological constant.Comment: 12 pages, to be published in Phys. Rev.
Higher Derivative Operators from Scherk-Schwarz Supersymmetry Breaking on T^2/Z_2
In orbifold compactifications on T^2/Z_2 with Scherk-Schwarz supersymmetry
breaking, it is shown that (brane-localised) superpotential interactions and
(bulk) gauge interactions generate at one-loop higher derivative counterterms
to the mass of the brane (or zero-mode of the bulk) scalar field. These
brane-localised operators are generated by integrating out the bulk modes of
the initial theory which, although supersymmetric, is nevertheless
non-renormalisable. It is argued that such operators, of non-perturbative
origin and not protected by non-renormalisation theorems, are generic in
orbifold compactifications and play a crucial role in the UV behaviour of the
two-point Green function of the scalar field self-energy. Their presence in the
action with unknown coefficients prevents one from making predictions about
physics at (momentum) scales close to/above the compactification scale(s). Our
results extend to the case of two dimensional orbifolds, previous findings for
S^1/Z_2 and S^1/(Z_2 x Z_2') compactifications where brane-localised higher
derivative operators are also dynamically generated at loop level, regardless
of the details of the supersymmetry breaking mechanism. We stress the
importance of these operators for the hierarchy and the cosmological constant
problems in compactified theories.Comment: 23 pages, LaTeX, one figure, published version in JHE
The Fayet-Iliopoulos D-term and its renormalisation in the MSSM
We consider the renormalisation of the Fayet-Iliopoulos D-term in a
softly-broken supersymmetric gauge theory with a non-simple gauge group
containing an abelian factor, and present the associated beta-function through
three loops. We also include in an appendix the result for several abelian
factors. We specialise to the case of the minimal supersymmetric standard model
(MSSM), and investigate the behaviour of the Fayet-Iliopoulos coupling for
various boundary conditions at the unification scale. We focus particularly on
the case of non-standard soft supersymmetry breaking couplings, for which the
Fayet-Iliopoulos coupling evolves significantly between the unification scale
and the weak scale.Comment: 18 pages, Revtex, 2 figures. Expanded version including general
results for gauge groups with several abelian factors. Minor typos correcte
The Fayet-Iliopoulos D-term and its renormalisation in softly-broken supersymmetric theories
We consider the renormalisation of the Fayet-Iliopoulos D-term in a
softly-broken abelian supersymmetric theory, and calculate the associated
beta-function through three loops. We show that there exists (at least through
three loops) a renormalisation group invariant trajectory for the coefficient
of the D-term, corresponding to the conformal anomaly solution for the soft
masses and couplings.Comment: 30 pages, Revtex, 15 Figures. Minor changes, and inadvertent omission
of author from this abstract correcte
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