402 research outputs found
Breaking the electroweak symmetry and supersymmetry by a compact extra dimension
We revisit in some more detail a recent specific proposal for the breaking of
the electroweak symmetry and of supersymmetry by a compact extra dimension.
Possible mass terms for the Higgs and the matter hypermultiplets are considered
and their effects on the spectrum analyzed. Previous conclusions are reinforced
and put on firmer ground.Comment: 25 pages, LaTeX, 9 eps figure
Fine tuning as an indication of physics beyond the MSSM
We investigate the amount of fine tuning of the electroweak scale in the
presence of new physics beyond the MSSM, parametrized by higher dimensional
operators. We show that these significantly reduce the MSSM fine tuning to
Delta<10 for a Higgs mass between the LEPII bound and 130 GeV, and a
corresponding scale M_* of new physics as high as 30 to 65 times the Higgsino
mass. If the fine-tuning criterion is indeed of physical relevance, the
findings indicate the presence of new physics in the form of new states of mass
of O(M_*) that generated the effective operators in the first instance. At
small these states can be a gauge singlet or a SU(2) triplet. We
derive analytical results for the EW scale fine-tuning for the MSSM with higher
dimensional operators, including the quantum corrections which are also
applicable to the pure MSSM case in the limit the coefficients of the higher
dimension operators vanish. A general expression for the fine-tuning is also
obtained for an arbitrary two-Higgs doublet potential.Comment: 27 pages, 6 Figures; Eqs.(15)-(18) and (A.2)-(A.5) simplified;
figures 1-3 update
Testing SUSY
If SUSY provides a solution to the hierarchy problem then supersymmetric
states should not be too heavy. This requirement is quantified by a fine tuning
measure that provides a quantitative test of SUSY as a solution to the
hierarchy problem. The measure is useful in correlating the impact of the
various experimental measurements relevant to the search for supersymmetry and
also in identifying the most sensitive measurements for testing SUSY. In this
paper we apply the measure to the CMSSM, computing it to two-loop order and
taking account of current experimental limits and the constraint on dark matter
abundance. Using this we determine the present limits on the CMSSM parameter
space and identify the measurements at the LHC that are most significant in
covering the remaining parameter space. Without imposing the LEP Higgs mass
bound we show that the smallest fine tuning (1:13) consistent with a relic
density within the WMAP bound corresponds to a Higgs mass of 1142 GeV.
Fine tuning rises rapidly for heavier Higgs.Comment: 12 pages, 7 figures; references added, figures updated for extended
parameter space sca
Radiative Corrections to Neutralino and Chargino Masses in the Minimal Supersymmetric Model
We determine the neutralino and chargino masses in the MSSM at one-loop. We
perform a Feynman diagram calculation in the on-shell renormalization scheme,
including quark/squark and lepton/slepton loops. We find generically the
corrections are of order 6%. For a 20 GeV neutralino the corrections can be
larger than 20%. The corrections change the region of
parameter space which is ruled out by LEP data. We demonstrate that, e.g., for
a given and the lower limit on the parameter can shift
by 20 GeV.Comment: 11 pages, JHU-TIPAC-930030, PURD-TH-93-13, uses epsf.sty, 6 uuencoded
postscript figures, added one sentence and a referenc
Testing SUSY at the LHC: Electroweak and Dark matter fine tuning at two-loop order
In the framework of the Constrained Minimal Supersymmetric Standard Model
(CMSSM) we evaluate the electroweak fine tuning measure that provides a
quantitative test of supersymmetry as a solution to the hierarchy problem.
Taking account of current experimental constraints we compute the fine tuning
at two-loop order and determine the limits on the CMSSM parameter space and the
measurements at the LHC most relevant in covering it. Without imposing the
LEPII bound on the Higgs mass, it is shown that the fine tuning computed at
two-loop has a minimum corresponding to a Higgs mass GeV. Adding the constraint that the SUSY dark matter relic density should be
within present bounds we find corresponding to GeV
and this rises to ( GeV) for SUSY dark matter
abundance within 3 of the WMAP constraint. We extend the analysis to
include the contribution of dark matter fine tuning. In this case the overall
fine tuning and Higgs mass are only marginally larger for the case SUSY dark
matter is subdominant and rises to ( GeV) for
the case of SUSY dark matter saturates the WMAP bound. For a Higgs mass above
these values, fine tuning rises exponentially fast. The CMSSM spectrum that
corresponds to minimal fine tuning is computed and provides a benchmark for
future searches. It is characterised by heavy squarks and sleptons and light
neutralinos, charginos and gluinos.Comment: 36 pages, 24 figure
The fine-tuning cost of the likelihood in SUSY models
In SUSY models, the fine tuning of the electroweak (EW) scale with respect to
their parameters gamma_i={m_0, m_{1/2}, mu_0, A_0, B_0,...} and the maximal
likelihood L to fit the experimental data are usually regarded as two different
problems. We show that, if one regards the EW minimum conditions as constraints
that fix the EW scale, this commonly held view is not correct and that the
likelihood contains all the information about fine-tuning. In this case we show
that the corrected likelihood is equal to the ratio L/Delta of the usual
likelihood L and the traditional fine tuning measure Delta of the EW scale. A
similar result is obtained for the integrated likelihood over the set
{gamma_i}, that can be written as a surface integral of the ratio L/Delta, with
the surface in gamma_i space determined by the EW minimum constraints. As a
result, a large likelihood actually demands a large ratio L/Delta or
equivalently, a small chi^2_{new}=chi^2_{old}+2*ln(Delta). This shows the
fine-tuning cost to the likelihood (chi^2_{new}) of the EW scale stability
enforced by SUSY, that is ignored in data fits. A good
chi^2_{new}/d.o.f.\approx 1 thus demands SUSY models have a fine tuning amount
Delta<<exp(d.o.f./2), which provides a model-independent criterion for
acceptable fine-tuning. If this criterion is not met, one can thus rule out
SUSY models without a further chi^2/d.o.f. analysis. Numerical methods to fit
the data can easily be adapted to account for this effect.Comment: 10 pages (v3: small comment added
Deconstructing Non-Abelian Gauge Theories at One Loop
Deconstruction of 5D Yang-Mills gauge theories is studied in next-to-leading
order accuracy. We calculate one-loop corrections to the mass spectrum of the
non-linear gauged sigma-model, which is the low energy effective theory of the
deconstructed theory. Renormalization is carried out following the standard
procedure of effective field theories. The relation between the radius of the
compactified fifth dimension and the symmetry breaking scale of the non-linear
sigma-model is modified by radiative corrections. We demonstrate that one can
match the low lying spectrum of the gauge boson masses of the effective 4D
gauged non-linear sigma-model to the Kaluza-Klein modes of the 5D theory at
one-loop accuracy
Anomalies, Fayet-Iliopoulos terms and the consistency of orbifold field theories
We study the consistency of orbifold field theories and clarify to what
extent the condition of having an anomaly-free spectrum of zero-modes is
sufficient to guarantee it. Preservation of gauge invariance at the quantum
level is possible, although at the price, in general, of introducing operators
that break the 5d local parity. These operators are, however, perfectly
consistent with the orbifold projection. We also clarify the relation between
localized Fayet-Iliopoulos (FI) terms and anomalies. These terms can be
consistently added, breaking neither local supersymmetry nor the gauge
symmetry. In the framework of supergravity the localized FI term arises as the
boundary completion of a bulk interaction term: given the bulk Lagrangian the
FI is fixed by gauge invariance.Comment: 31 pages, 1 figure. v2: some typos corrected, references adde
Precise Prediction for M_W in the MSSM
We present the currently most accurate evaluation of the W boson mass, M_W,
in the Minimal Supersymmetric Standard Model (MSSM). The full complex phase
dependence at the one-loop level, all available MSSM two-loop corrections as
well as the full Standard Model result have been included. We analyse the
impact of the different sectors of the MSSM at the one-loop level with a
particular emphasis on the effect of the complex phases. We discuss the
prediction for M_W based on all known higher-order contributions in
representative MSSM scenarios. Furthermore we obtain an estimate of the
remaining theoretical uncertainty from unknown higher-order corrections.Comment: 38 pages, 25 figures. Minor corrections, additional reference
Beyond the MSSM Higgs with d=6 effective operators
We continue a previous study of the MSSM Higgs Lagrangian extended by all
effective operators of dimension d=6 that can be present beyond the MSSM,
consistent with its symmetries. By supersymmetry, such operators also extend
the neutralino and chargino sectors, and the corresponding component fields
Lagrangian is computed onshell. The corrections to the neutralino and chargino
masses, due to these operators, are computed analytically in function of the
MSSM corresponding values. For individual operators, the corrections are small,
of few GeV for the constrained MSSM (CMSSM) viable parameter space. We
investigate the correction to the lightest Higgs mass, which receives, from
individual operators, a supersymmetric correction of up to 4 (6) GeV above the
2-loop leading-log CMSSM value, from those CMSSM phase space points with: EW
fine tuning Delta<200, consistent with WMAP relic density (3), and for
a scale of the operators of M=10 (8) TeV, respectively. Applied to the CMSSM
point of minimal fine tuning (Delta=18), such increase gives an upper limit
GeV, respectively. The increase of m_h from individual
operators can be larger ( 10-30 GeV) for those CMSSM phase space points
with Delta>200; these can now be phenomenologically viable, with reduced Delta,
and this includes those points that would have otherwise violated the LEP2
bound by this value. The neutralino/chargino Lagrangian extended by the
effective operators can be used in studies of dark matter relic density within
extensions of the MSSM, by implementing it in public codes like micrOMEGAs.Comment: 36 pages, Latex, 16 figures (v2: minor changes, corrected typos
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