6,178 research outputs found
Resonance at 125 GeV: Higgs or Dilaton/Radion?
We consider the possibility that the new particle that has been observed at
125 GeV is not the Standard Model (SM) Higgs, but instead the dilaton
associated with an approximate conformal symmetry that has been spontaneously
broken. We focus on dilatons that arise from theories of technicolor, or from
theories of the Higgs as a pseudo-Nambu-Goldstone boson (pNGB), that involve
strong conformal dynamics in the ultraviolet. In the pNGB case, we are
considering a framework where the Higgs particle is significantly heavier than
the dilaton and has therefore not yet been observed. In each of the technicolor
and pNGB scenarios, we study both the case when the SM fermions and gauge
bosons are elementary, and the case when they are composites of the strongly
interacting sector. Our analysis incorporates conformal symmetry violating
effects, which are necessarily present since the dilaton is not massless, and
is directly applicable to a broad class of models that stabilize the weak scale
and involve strong conformal dynamics. Since the AdS/CFT correspondence relates
the radion in Randall-Sundrum (RS) models to the dilaton, our results also
apply to RS models with the SM fields localized on the infrared brane, or in
the bulk. We identify the parameters that can be used to distinguish the
dilatons associated with the several different classes of theories being
considered from each other, and from the SM Higgs. We perform a fit to all the
available data from several experiments and highlight the key observations to
extract these parameters. We find that at present, both the technicolor and
pNGB dilaton scenarios provide a good fit to the data, comparable to the SM
Higgs. We indicate the future observations that will help to corroborate or
falsify each scenario.Comment: 41 pages, 4 figures. Analysis updated using current theoretical
limits on dimensions of CFT operators. References added. Version to appear on
JHE
A Supersymmetric Theory of Flavor and R Parity
We construct a renormalizable, supersymmetric theory of flavor and parity
based on the discrete flavor group . The model can account for all the
masses and mixing angles of the Standard Model, while maintaining sufficient
squark degeneracy to circumvent the supersymmetric flavor problem. By starting
with a simpler set of flavor symmetry breaking fields than we have suggested
previously, we construct an economical Froggatt-Nielsen sector that generates
the desired elements of the fermion Yukawa matrices. With the particle content
above the flavor scale completely specified, we show that all renormalizable
-parity-violating interactions involving the ordinary matter fields are
forbidden by the flavor symmetry. Thus, parity arises as an accidental
symmetry in our model. Planck-suppressed operators that violate parity, if
present, can be rendered harmless by taking the flavor scale to be GeV.Comment: 28 pp. LaTeX, 1 Postscript Figur
Higgs-gauge unification without tadpoles
In orbifold gauge theories localized tadpoles can be radiatively generated at
the fixed points where U(1) subgroups are conserved. If the Standard Model
Higgs fields are identified with internal components of the bulk gauge fields
(Higgs-gauge unification) in the presence of these tadpoles the Higgs mass
becomes sensitive to the UV cutoff and electroweak symmetry breaking is
spoiled. We find the general conditions, based on symmetry arguments, for the
absence/presence of localized tadpoles in models with an arbitrary number of
dimensions D. We show that in the class of orbifold compactifications based on
T^{D-4}/Z_N (D even, N>2) tadpoles are always allowed, while on T^{D-4}/\mathbb
Z_2 (arbitrary D) with fermions in arbitrary representations of the bulk gauge
group tadpoles can only appear in D=6 dimensions. We explicitly check this with
one- and two-loops calculationsComment: 19 pages, 3 figures, axodraw.sty. v2: version to appear in Nucl.
Phys.
Deriving Boltzmann Equations from Kadanoff-Baym Equations in Curved Space-Time
To calculate the baryon asymmetry in the baryogenesis via leptogenesis
scenario one usually uses Boltzmann equations with transition amplitudes
computed in vacuum. However, the hot and dense medium and, potentially, the
expansion of the universe can affect the collision terms and hence the
generated asymmetry. In this paper we derive the Boltzmann equation in the
curved space-time from (first-principle) Kadanoff-Baym equations. As one
expects from general considerations, the derived equations are covariant
generalizations of the corresponding equations in Minkowski space-time. We find
that, after the necessary approximations have been performed, only the
left-hand side of the Boltzmann equation depends on the space-time metric. The
amplitudes in the collision term on the right--hand side are independent of the
metric, which justifies earlier calculations where this has been assumed
implicitly. At tree level, the matrix elements coincide with those computed in
vacuum. However, the loop contributions involve additional integrals over the
the distribution function.Comment: 14 pages, 5 figures, extended discussion of the constraint equations
and the solution for the spectral functio
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