84 research outputs found
Complete two-loop effective potential approximation to the lightest Higgs scalar boson mass in supersymmetry
I present a method for accurately calculating the pole mass of the lightest
Higgs scalar boson in supersymmetric extensions of the Standard Model, using a
mass-independent renormalization scheme. The Higgs scalar self-energies are
approximated by supplementing the exact one-loop results with the second
derivatives of the complete two-loop effective potential in Landau gauge. I
discuss the dependence of this approximation on the choice of renormalization
scale, and note the existence of particularly poor choices which fortunately
can be easily identified and avoided. For typical input parameters, the
variation in the calculated Higgs mass over a wide range of renormalization
scales is found to be of order a few hundred MeV or less, and is significantly
improved over previous approximations.Comment: 5 pages, 1 figure. References added, sample test model parameters
listed, minor wording change
К определению понятий коммуникация, интеркультурная коммуникация и коммуникативистика
The Strong Electrostatic Adsorption (SEA) method was applied to the rational design of a promoted Co catalyst for Fischer–Tropsch (FT) synthesis. A series of Mn/Co/TiO2 catalysts were prepared by selective deposition of the [MnO4] anion onto the supported Co3O4 phase. Qualitative ICP-OES and XPS measurements of the prepared catalysts with increasing Mn loading displayed the preferential association of the Mn species with Co3O4 and not the TiO2 support. The SEA preparation method seemed to minimize the migration of Mn away from the Co to the TiO2 support during reduction procedures to ensure a more intimate interaction between the Mn and the Co species during FT reactivity measurements. This led to an increase in light olefins, C5+ selectivity and chain growth probability. It is anticipated that the SEA preparation method is a viable synthesis strategy for other promoted and/or bimetallic catalyst systems where intimate contact between the catalyst components is highly desired
On the Meaning of the String-Inspired Noncommutativity and its Implications
We propose an alternative interpretation for the meaning of noncommutativity
of the string-inspired field theories and quantum mechanics. Arguments are
presented to show that the noncommutativity generated in the stringy context
should be assumed to be only between the particle coordinate observables, and
not of the spacetime coordinates. Some implications of this fact for
noncomutative field theories and quantum mechanics are discussed. In
particular, a consistent interpretation is given for the wavefunction in
quantum mechanics. An analysis of the noncommutative theories in the
Schr\"odinger formulation is performed employing a generalized quantum
Hamilton-Jacobi formalism. A formal structure for noncommutative quantum
mechanics, richer than the one of noncommutative quantum field theory, comes
out. Conditions for the classical and commutative limits of these theories have
also been determined and applied in some examples.Comment: References, comments, and footnotes are included; some changes in
section
Two-loop scalar self-energies in a general renormalizable theory at leading order in gauge couplings
I present results for the two-loop self-energy functions for scalars in a
general renormalizable field theory, using mass-independent renormalization
schemes based on dimensional regularization and dimensional reduction. The
results are given in terms of a minimal set of loop-integral basis functions,
which are readily evaluated numerically by computers. This paper contains the
contributions corresponding to the Feynman diagrams with zero or one vector
propagator lines. These are the ones needed to obtain the pole masses of the
neutral and charged Higgs scalar bosons in supersymmetry, neglecting only the
purely electroweak parts at two-loop order. A subsequent paper will present the
results for the remaining diagrams, which involve two or more vector lines.Comment: 26 pages, 4 figures, revtex4, axodraw.sty. Version 2: sentence after
eq. (A.13) corrected, references added. Version 3: typos in eqs. (5.17),
(5.20), (5.21), (5.32) are corrected. Also, the MSbar versions of eqs. (5.32)
and (5.33) are now include
Top-squark searches at the Tevatron in models of low-energy supersymmetry breaking
We study the production and decays of top squarks (stops) at the Tevatron
collider in models of low-energy supersymmetry breaking. We consider the case
where the lightest Standard Model (SM) superpartner is a light neutralino that
predominantly decays into a photon and a light gravitino. Considering the
lighter stop to be the next-to-lightest Standard Model superpartner, we analyze
stop signatures associated with jets, photons and missing energy, which lead to
signals naturally larger than the associated SM backgrounds. We consider both
2-body and 3-body decays of the top squarks and show that the reach of the
Tevatron can be significantly larger than that expected within either the
standard supergravity models or models of low-energy supersymmetry breaking in
which the stop is the lightest SM superpartner. For a modest projection of the
final Tevatron luminosity, L = 4 fb-1, stop masses of order 300 GeV are
accessible at the Tevatron collider in both 2-body and 3-body decay modes. We
also consider the production and decay of ten degenerate squarks that are the
supersymmetric partners of the five light quarks. In this case we find that
common squark masses up to 360 GeV are easily accessible at the Tevatron
collider, and that the reach increases further if the gluino is light.Comment: 32 pages, 9 figures; references adde
CP Violation in Supersymmetric U(1)' Models
The supersymmetric CP problem is studied within superstring-motivated
extensions of the MSSM with an additional U(1)' gauge symmetry broken at the
TeV scale. This class of models offers an attractive solution to the mu problem
of the MSSM, in which U(1)' gauge invariance forbids the bare mu term, but an
effective mu parameter is generated by the vacuum expectation value of a
Standard Model singlet S which has superpotential coupling of the form SH_uH_d
to the electroweak Higgs doublets. The effective mu parameter is thus
dynamically determined as a function of the soft supersymmetry breaking
parameters, and can be complex if the soft parameters have nontrivial
CP-violating phases. We examine the phenomenological constraints on the
reparameterization invariant phase combinations within this framework, and find
that the supersymmetric CP problem can be greatly alleviated in models in which
the phase of the SU(2) gaugino mass parameter is aligned with the soft
trilinear scalar mass parameter associated with the SH_uH_d coupling. We also
study how the phases filter into the Higgs sector, and find that while the
Higgs sector conserves CP at the renormalizable level to all orders of
perturbation theory, CP violation can enter at the nonrenormalizable level at
one-loop order. In the majority of the parameter space, the lightest Higgs
boson remains essentially CP even but the heavier Higgs bosons can exhibit
large CP-violating mixings, similar to the CP-violating MSSM with large mu
parameter.Comment: 29 pp, 3 figs, 2 table
The stochastic spectator
We study the stochastic distribution of spectator fields predicted in different slow-roll inflation backgrounds. Spectator fields have a negligible energy density during inflation but may play an important dynamical role later, even giving rise to primordial density perturbations within our observational horizon today. During de-Sitter expansion there is an equilibrium solution for the spectator field which is often used to estimate the stochastic distribution during slow-roll inflation. However slow roll only requires that the Hubble rate varies slowly compared to the Hubble time, while the time taken for the stochastic distribution to evolve to the de-Sitter equilibrium solution can be much longer than a Hubble time. We study both chaotic (monomial) and plateau inflaton potentials, with quadratic, quartic and axionic spectator fields. We give an adiabaticity condition for the spectator field distribution to relax to the de-Sitter equilibrium, and find that the de-Sitter approximation is never a reliable estimate for the typical distribution at the end of inflation for a quadratic spectator during monomial inflation. The existence of an adiabatic regime at early times can erase the dependence on initial conditions of the final distribution of field values. In these cases, spectator fields acquire sub-Planckian expectation values. Otherwise spectator fields may acquire much larger field displacements than suggested by the de-Sitter equilibrium solution. We quantify the information about initial conditions that can be obtained from the final field distribution. Our results may have important consequences for the viability of spectator models for the origin of structure, such as the simplest curvaton models
Physics Implications of Flat Directions in Free Fermionic Superstring Models I: Mass Spectrum and Couplings
From the "top-down" approach we investigate physics implications of the class
of D- and F- flat directions formed from non-Abelian singlets which are proven
flat to all orders in the nonrenormalizable superpotential, for a prototype
quasi-realistic free fermionic string model with the standard model gauge group
and three families (CHL5). These flat directions have at least an additional
U(1)' unbroken at the string scale. For each flat direction, the complete set
of effective mass terms and effective trilinear superpotential terms in the
observable sector are computed to all orders in the VEV's of the fields in the
flat direction. The "string selection-rules" disallow a large number of
couplings allowed by gauge invariance, resulting in a massless spectrum with a
large number of exotics, in most cases excluded by experiment, thus signifying
a generic flaw of these models. Nevertheless, the resulting trilinear couplings
of the massless spectrum possess a number of interesting features which we
analyse for two representative flat directions: for the fermion texture;
baryon- and lepton-number violating couplings; R-parity breaking; non-canonical
mu terms; and the possibility of electroweak and intermediate scale symmetry
breaking scenarios for U(1)'. The gauge coupling predictions are obtained in
the electroweak scale case. Fermion masses possess t-b and tau-mu universality,
with the string scale Yukawa couplings g and , respectively.
Fermion textures are present for certain flat directions, but only in the
down-quark sector. Baryon- and lepton- number violating couplings can trigger
proton-decay, oscillations, leptoquark interactions and R-parity
violation, leading to the absence of a stable LSP.Comment: 36 pages, 5 tables, 4 figures, RevTeX, minor change
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