137 research outputs found
Fine-Tuning Constraints on Supergravity Models
We discuss fine-tuning constraints on supergravity models. The tightest
constraints come from the experimental mass limits on two key particles: the
lightest CP even Higgs boson and the gluino. We also include the lightest
chargino which is relevant when universal gaugino masses are assumed. For each
of these particles we show how fine-tuning increases with the experimental mass
limit, for four types of supergravity model: minimal supergravity, no-scale
supergravity (relaxing the universal gaugino mass assumption), D-brane models
and anomaly mediated supersymmetry breaking models. Among these models, the
D-brane model is less fine tuned.The experimental propects for an early
discovery of Higgs and supersymmetry at LEP and the Tevatron are discussed in
this framework.Comment: 17 pages, Latex, including 5 eps figure
SO(10) unified models and soft leptogenesis
Motivated by the fact that, in some realistic models combining SO(10) GUTs
and flavour symmetries, it is not possible to achieve the required baryon
asymmetry through the CP asymmetry generated in the decay of right-handed
neutrinos, we take a fresh look on how deep this connection is in SO(10). The
common characteristics of these models are that they use the see-saw with
right-handed neutrinos, predict a normal hierarchy of masses for the neutrinos
observed in oscillating experiments and in the basis where the right-handed
Majorana mass is diagonal, the charged lepton mixings are tiny.
In addition these models link the up-quark Yukawa matrix to the neutrino
Yukawa matrix Y^\nu with the special feature of Y^\nu_{11}-> 0 Using this
condition, we find that the required baryon asymmetry of the Universe can be
explained by the soft leptogenesis using the soft B parameter of the second
lightest right-handed neutrino whose mass turns out to be around 10^8 GeV. It
is pointed out that a natural way to do so is to use no-scale supergravity
where the value of B ~1 GeV is set through gauge-loop corrections.Comment: 26 pages, 2 figures. Added references, new appendix of a relevant fit
and improved comment
The Gaugino Code
Gauginos might play a crucial role in the search for supersymmetry at the
Large Hadron Collider (LHC). Mass predictions for gauginos are rather robust
and often related to the values of the gauge couplings. We analyse the ratios
of gaugino masses in the LHC energy range for various schemes of supersymmetry
breakdown and mediation. Three distinct mass patterns emerge.Comment: 42 pages, Latex; a discussion of deflected anomaly mediation added,
references adde
Neutralino Dark Matter from MSSM Flat Directions in light of WMAP Result
The minimal supersymmetric standard model (MSSM) has a truly supersymmetric
way to explain both the baryon asymmetry and cold dark matter in the present
Universe, that is, ``Affleck-Dine baryo/DM-genesis.'' The associated late-time
decay of Q-balls directly connects the origins of the baryon asymmetry and dark
matter, and also predicts a specific nature of the LSP. In this paper, we
investigate the prospects for indirect detection of these dark matter
candidates observing high energy neutrino flux from the Sun, and hard positron
flux from the halo. We also update the previous analysis of the direct
detection in hep-ph/0205044 by implementing the recent result from WMAP
satellite.Comment: 32 pages, including 40 figure
Effective Lagrangian for and Vertices in the mSUGRA model
Complete expressions of the and vertices are
derived in the framework of supersymmetry with minimal flavor violation. With
the minimal supergravity (mSUGRA) model, a numerical analysis of the
supersymmetric contributions to the Wilson Coefficients at the weak scale is
presented.Comment: 12 pages + 7 ps figures, Late
Atmospheric Neutrinos Can Make Beauty Strange
The large observed mixing angle in atmospheric neutrinos, coupled with Grand
Unification, motivates the search for a large mixing between right-handed
strange and bottom squarks. Such mixing does not appear in the standard CKM
phenomenology, but may induce significant b to s transitions through gluino
diagrams. Working in the mass eigenbasis, we show quantitatively that an order
one effect on CP violation in B_d to phi+K_S is possible due to a large mixing
between right-handed b and s squarks, while still satisfying constraints from b
to s + gamma. We also include the effect of right- and left-handed bottom
squark mixing proportional to m_b*mu*tan(beta). For small mu*tan(beta) there
may also be a large effect in B_s mixing correlated with a large effect in B_d
to phi+K_S, typically mixing effects are greater than 100 ps^{-1}, an
unambiguous signal of new physics at Tevatron Run II.Comment: 32 pages, LaTeX. Corrected a factor of two mistake in the code; the
possible impact on B -> phi K_s became larger. Figures and discussion
updated, a reference adde
Higgs boson mass limits in perturbative unification theories
Motivated in part by recent demonstrations that electroweak unification into
a simple group may occur at a low scale, we detail the requirements on the
Higgs mass if the unification is to be perturbative. We do this for the
Standard Model effective theory, minimal supersymmetry, and next-to-minimal
supersymmetry with an additional singlet field. Within the Standard Model
framework, we find that perturbative unification with sin2(thetaW)=1/4 occurs
at Lambda=3.8 TeV and requires mh<460 GeV, whereas perturbative unification
with sin2(thetaW)=3/8 requires mh<200 GeV. In supersymmetry, the presentation
of the Higgs mass predictions can be significantly simplified, yet remain
meaningful, by using a single supersymmetry breaking parameter Delta_S. We
present Higgs mass limits in terms of Delta_S for the minimal supersymmetric
model and the next-to-minimal supersymmetric model. We show that in
next-to-minimal supersymmetry, the Higgs mass upper limit can be as large as
500 GeV even for moderate supersymmetry masses if the perturbative unification
scale is low (e.g., Lambda=10 TeV).Comment: 20 pages, latex, 6 figures, references adde
The cosmic ray positron excess and neutralino dark matter
Using a new instrument, the HEAT collaboration has confirmed the excess of
cosmic ray positrons that they first detected in 1994. We explore the
possibility that this excess is due to the annihilation of neutralino dark
matter in the galactic halo. We confirm that neutralino annihilation can
produce enough positrons to make up the measured excess only if there is an
additional enhancement to the signal. We quantify the `boost factor' that is
required in the signal for various models in the Minimal Supersymmetric
Standard Model parameter space, and study the dependence on various parameters.
We find models with a boost factor greater than 30. Such an enhancement in the
signal could arise if we live in a clumpy halo. We discuss what part of
supersymmetric parameter space is favored (in that it gives the largest
positron signal), and the consequences for other direct and indirect searches
of supersymmetric dark matter.Comment: 11 pages, 6 figures, matches published version (PRD
Particle Physics Approach to Dark Matter
We review the main proposals of particle physics for the composition of the
cold dark matter in the universe. Strong axion contribution to cold dark matter
is not favored if the Peccei-Quinn field emerges with non-zero value at the end
of inflation and the inflationary scale is superheavy since, under these
circumstances, it leads to unacceptably large isocurvature perturbations. The
lightest neutralino is the most popular candidate constituent of cold dark
matter. Its relic abundance in the constrained minimal supersymmetric standard
model can be reduced to acceptable values by pole annihilation of neutralinos
or neutralino-stau coannihilation. Axinos can also contribute to cold dark
matter provided that the reheat temperature is adequately low. Gravitinos can
constitute the cold dark matter only in limited regions of the parameter space.
We present a supersymmetric grand unified model leading to violation of Yukawa
unification and, thus, allowing an acceptable b-quark mass within the
constrained minimal supersymmetric standard model with mu>0. The model
possesses a wide range of parameters consistent with the data on the cold dark
matter abundance as well as other phenomenological constraints. Also, it leads
to a new version of shifted hybrid inflation.Comment: 32 pages including 6 figures, uses svmult.cls, some clarifications
added, lectures given at the Third Aegean Summer School "The Invisible
Universe: Dark Matter and Dark Energy", 26 September-1 October 2005, Karfas,
Island of Chios, Greece (to appear in the proceedings
Higgs Scalars in the Minimal Non-minimal Supersymmetric Standard Model
We consider the simplest and most economic version among the proposed
non-minimal supersymmetric models, in which the -parameter is promoted to
a singlet superfield, whose all self-couplings are absent from the
renormalizable superpotential. Such a particularly simple form of the
renormalizable superpotential may be enforced by discrete -symmetries which
are extended to the gravity-induced non-renormalizable operators as well. We
show explicitly that within the supergravity-mediated supersymmetry-breaking
scenario, the potentially dangerous divergent tadpoles associated with the
presence of the gauge singlet first appear at loop levels higher than 5 and
therefore do not destabilize the gauge hierarchy. The model provides a natural
explanation for the origin of the -term, without suffering from the
visible axion or the cosmological domain-wall problem. Focusing on the Higgs
sector of this minimal non-minimal supersymmetric standard model, we calculate
its effective Higgs potential by integrating out the dominant quantum effects
due to stop squarks. We then discuss the phenomenological implications of the
Higgs scalars predicted by the theory for the present and future high-energy
colliders. In particular, we find that our new minimal non-minimal
supersymmetric model can naturally accommodate a relatively light charged Higgs
boson, with a mass close to the present experimental lower bound.Comment: 63 pages (12 figures), extended versio
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