45 research outputs found

### The nature of the bonds in the iron silicide, FeSi, and related crystals

The iron silicide FeSi has been reinvestigated by X-ray photography of single crystals, and the reported structure for the substance has been verified. The space group is T^4-P2_13, with a_0 = 4.489 ± 0.005 A. Four iron atoms and four silicon atoms are in positions (x, x, x; x + 1/2, 1/2} - x, x[bar]; undefined), with x_(Fe) = 0.1370 ± 0.0020 and x_(Si) = 0.842 ± 0.004. A detailed discussion of the structure and the values of the interatomic distances has been given, by application of the resonating-valence-bond theory, and it has been shown that the interatomic distances are compatible with those found for elementary iron and elementary silicon

### The chiral logs of the K -> pi pi amplitude

I calculate the leading logarithmic contributions up to two-loop order of the
octet part of the K -> pi pi amplitude. This sector of the weak chiral
Lagrangian is believed to be the main source of the enhancement of the I=0
relative to the I=2 K -> pi pi amplitude, the so-called Delta I = 1/2 rule. I
discuss the procedure of chiral extrapolations of lattice data specific to K ->
pi pi decays and study the implication of the present calculation on these
numerically. The latter reinforces the fact that one has to expect a large
enhancement of the I=0 part of the amplitude due to re-scattering effects
between the three mesons.Comment: 20 pages, 4 figures, uses axodra

### Standard Model Higgs boson searches with the ATLAS detector at the Large Hadron Collider

The investigation of the mechanism responsible for electroweak symmetry
breaking is one of the most important tasks of the scientific program of the
Large Hadron Collider. The experimental results on the search of the Standard
Model Higgs boson with 1 to 2 fb^-1 of proton proton collision data at sqrt s=7
TeV recorded by the ATLAS detector are presented and discussed. No significant
excess of events is found with respect to the expectations from Standard Model
processes, and the production of a Higgs boson is excluded at 95% Confidence
Level for the mass regions 144-232, 256-282 and 296-466 GeV.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in
"Pramana - journal of phsyics". 11 pages, 13 figure

### Technicolor Theories with Negative S

We show that the pseudo Nambu--Goldstone boson contribution to the
Peskin--Takeuchi electroweak parameter $S$ can be negative in a class of
technicolor theories. This negative contribution can be large enough to cancel
the positive techni-hadron contribution, showing that electroweak precision
tests alone cannot be used to rule out technicolor as the mechanism of
electroweak symmetry breaking.Comment: (LBL-32893, UCB-PTH 92/34, 10 pages; we added a discussion of
uncertainties, fine-tuning, and SU(2) asymptotic freedom; the conclusions are
unchanged.

### The Electroweak Chiral Lagrangian and CP-Violating Effects in Technicolor Theories

We estimate the CP-violating $WW\gamma$ and $WWZ$ anomalous form factors,
arising from CP-violating interactions in extended technicolor theories, and
discuss their future experimental detectability. The electric dipole moment of
the $W$ boson is found to be as large as {\cal O}(10^{-21}) \; \mbox{e cm}.
We connect the CP-odd $WW\gamma$ and $WWZ$ couplings to the corresponding
CP-violating electroweak chiral lagrangian operators. The electric dipole
moments of the neutron and the electron in technicolor theories are estimated
to be as large as {\cal O}(10^{-26}) \; \mbox{e cm} and {\cal O}(10^{-29})
\; \mbox{e cm} respectively. We also suggest the potential to observe large
CP-violating technicolor effects in the decay $t \rightarrow b + W^+$.Comment: 34 pages, YCTP-P9-94, LaTex. (minor changes in wording and notation,
the figures are appended at the end as one postscript file

### A strongly first order electroweak phase transition from strong symmetry-breaking interactions

We argue that a strongly first order electroweak phase transition is natural
in the presence of strong symmetry-breaking interactions, such as technicolor.
We demonstrate this using an effective linear scalar theory of the
symmetry-breaking sector.Comment: LaTex, 15 pages, 3 figures in EPS format. Phys. Rev. D approved
Typographically Correct version, minor grammatical change

### Gauge-Higgs Unification In Spontaneously Created Fuzzy Extra Dimensions

We propose gauge-Higgs unification in fuzzy extra dimensions as a possible
solution to the Higgs naturalness problem. In our approach, the fuzzy extra
dimensions are created spontaneously as a vacuum solution of certain
four-dimensional gauge theory. As an example, we construct a model which has a
fuzzy torus as its vacuum. The Higgs field in our model is associated with the
Wilson loop wrapped on the fuzzy torus. We show that the quadratic divergence
in the mass of the Higgs field in the one-loop effective potential is absent.
We then argue based on symmetries that the quantum corrections to the Higgs
mass is suppressed including all loop contributions. We also consider a
realization on the worldvolume theory of D3-branes probing $C^3/(Z_N \times
Z_N)$ orbifold with discrete torsion.Comment: 1+38 pages, 4 figures v2: refs adde

### Hierarchical Neutrino Mass Matrices, CP violation and Leptogenesis

In this work we study examples of hierarchical neutrino mass matrices
inspired by family symmetries, compatible with experiments on neutrino
oscillations, and for which there is a connection among the low energy CP
violation phase associated to neutrino oscillations, the phases appearing in
the amplitude of neutrinoless double beta decay, and the phases relevant for
leptogenesis. In particular, we determine the predictions from a texture based
on an underlying SU(3) family symmetry together with a GUT symmetry, and a
strong hierarchy for the masses of the heavy right handed Majorana masses. We
also give some examples of inverted hierarchies of neutrino masses, which may
be motivated in the context of U(1) family symmetries.Comment: 34 pages. Replaced with published version -typos, corrections and
references adde

### Analyticity, Crossing Symmetry and the Limits of Chiral Perturbation Theory

The chiral Lagrangian for Goldstone boson scattering is a power series
expansion in numbers of derivatives. Each successive term is suppressed by
powers of a scale, $\Lambda_\chi$, which must be less than of order $4\pi
f/\sqrt{N}$ where $f$ is the Goldstone boson decay constant and $N$ is the
number of flavors. The chiral expansion therefore breaks down at or below $4
\pi f/\sqrt{N}$. We argue that the breakdown of the chiral expansion is
associated with the appearance of physical states other than Goldstone bosons.
Because of crossing symmetry, some ``isospin'' channels will deviate from their
low energy behavior well before they approach the scale at which their low
energy amplitudes would violate unitarity. We argue that the estimates of
``oblique'' corrections from technicolor obtained by scaling from QCD are
untrustworthy.Comment: harvmac, 18 pages (3 figures), HUTP-92/A025, BUHEP-92-18, new version
fixes a TeX problem in little mod

### Flavor Mediation Delivers Natural SUSY

If supersymmetry (SUSY) solves the hierarchy problem, then naturalness
considerations coupled with recent LHC bounds require non-trivial superpartner
flavor structures. Such "Natural SUSY" models exhibit a large mass hierarchy
between scalars of the third and first two generations as well as degeneracy
(or alignment) among the first two generations. In this work, we show how this
specific beyond the standard model (SM) flavor structure can be tied directly
to SM flavor via "Flavor Mediation". The SM contains an anomaly-free SU(3)
flavor symmetry, broken only by Yukawa couplings. By gauging this flavor
symmetry in addition to SM gauge symmetries, we can mediate SUSY breaking via
(Higgsed) gauge mediation. This automatically delivers a natural SUSY spectrum.
Third-generation scalar masses are suppressed due to the dominant breaking of
the flavor gauge symmetry in the top direction. More subtly, the
first-two-generation scalars remain highly degenerate due to a custodial U(2)
symmetry, where the SU(2) factor arises because SU(3) is rank two. This
custodial symmetry is broken only at order (m_c/m_t)^2. SUSY gauge coupling
unification predictions are preserved, since no new charged matter is
introduced, the SM gauge structure is unaltered, and the flavor symmetry treats
all matter multiplets equally. Moreover, the uniqueness of the anomaly-free
SU(3) flavor group makes possible a number of concrete predictions for the
superpartner spectrum.Comment: 17 pages, 7 figures, 2 tables. v2 references added, minor changes to
flavor constraints and a little discussion adde