3,290 research outputs found
Symmetries of Two Higgs Doublet Model and CP violation
We use the invariance of physical picture under a change of Lagrangian, the
reparametrization invariance in the space of Lagrangians and its particular
case -- the rephrasing invariance, for analysis of the two-Higgs-doublet
extension of the SM. We found that some parameters of theory like tan beta are
reparametrization dependent and therefore cannot be fundamental. We use the
Z2-symmetry of the Lagrangian, which prevents a phi_1 phi_2 transitions,
and the different levels of its violation, soft and hard, to describe a
physical content of the model. In general, the broken Z2-symmetry allows for a
CP violation in the physical Higgs sector. We argue that the 2HDM with a soft
breaking of Z2-symmetry is a natural model in the description of EWSB. To
simplify an analysis we choose among different forms of Lagrangian describing
the same physical reality a specific one, in which the vacuum expectation
values of both Higgs fields are real. A possible CP violation in the Higgs
sector is described by using a two-step procedure with the first step identical
to a diagonalization of mass matrix for CP-even fields in the CP conserved
case. We find very simple necessary and sufficient condition for a CP violation
in the Higgs sector. We determine the range of parameters for which CP
violation and Flavor Changing Neutral Current effects are naturally small,what
corresponds to a small dimensionless mass parameter nu= Re m_{12}^2/(2v1v2). We
discuss how for small nu some Higgs bosons can be heavy, with mass up to about
0.6 TeV, without violating of the unitarity constraints. We discuss main
features of the large nu case, which corresponds for nu -> infty to a
decoupling of heavy Higgs bosons.Comment: 27 pages, extended discussion, references added, one figure, Revtex
Differential operators and Cherednik algebras
We establish a link between two geometric approaches to the representation
theory of rational Cherednik algebras of type A: one based on a noncommutative
Proj construction, used in [GS]; the other involving quantum hamiltonian
reduction of an algebra of differential operators, used in [GG].
In the present paper, we combine these two points of view by showing that the
process of hamiltonian reduction intertwines a naturally defined geometric
twist functor on D-modules with the shift functor for the Cherednik algebra.
That enables us to give a direct and relatively short proof of the key result,
[GS, Theorem 1.4] without recourse to Haiman's deep results on the n! theorem.
We also show that the characteristic cycles defined independently in these two
approaches are equal, thereby confirming a conjecture from [GG].Comment: 37 p
Evolution of Universe to the present inert phase
We assume that current state of the Universe can be described by the Inert
Doublet Model, containing two scalar doublets, one of which is responsible for
EWSB and masses of particles and the second one having no couplings to fermions
and being responsible for dark matter. We consider possible evolutions of the
Universe to this state during cooling down of the Universe after inflation. We
found that in the past Universe could pass through phase states having no DM
candidate. In the evolution via such states in addition to a possible EWSB
phase transition (2-nd order) the Universe sustained one 1-st order phase
transition or two phase transitions of the 2-nd order.Comment: 19 pages, 3 figure
Oscillon resonances and creation of kinks in particle collisions
We present a numerical study of the process of production of kink-antikink
pairs in the collision of particle-like states in the one-dimensional
model. It is shown that there are 3 steps in the process, the first step is to
excite the oscillon intermediate state in the particle collision, the second
step is a resonance excitation of the oscillon by the incoming perturbations,
and finally, the soliton-antisoliton pair can be created from the resonantly
excited oscillon. It is shown that the process depends fractally on the
amplitude of the perturbations and the wave number of the perturbation. We also
present the effective collective coordinate model for this process.Comment: 4 pages, 4 figures, revtex
Determining Sneutrino Masses and Physical Implications
In some areas of supersymmetry parameter space, sneutrinos are lighter than
the charginos and the next-to-lightest neutralino, and they decay into the
invisible neutrino plus lightest-neutralino channel with probability one. In
such a scenario they can be searched for in decays of charginos that are
pair-produced in e+e- collisions, and in associated sneutrino-chargino
production in photon-electron collisions. The sneutrino properties can be
determined with high accuracy from the edges of the decay energy spectra in the
first case and from threshold scans in the second. In the final part of the
report we investigate the mass difference of sneutrinos and charged sleptons
between the third and the first two generations in seesaw-type models of the
neutrino/sneutrino sector. For a wide range these mass differences are
sensitive to the seesaw scale.Comment: 20 p
Discovery limits for Techni-Omega production in Collisions
In a strongly-interacting electroweak sector with an isosinglet vector state,
such as the techni-omega, , the direct coupling
implies that an can be produced by fusion in
collisions. This is a unique feature for high energy or
colliders operating in an mode. We consider the processes and , both of which proceed via
an intermediate . We find that at a 1.5 TeV linear collider
operating in an mode with an integrated luminosity of 200 fb,
we can discover an for a broad range of masses and widths.Comment: To appear in the Proceedings of the 29th International Conference on
High Energy Physics, Vancouver, July 1998, 5 pages, Latex, 7 postscript
figure
Observation of Coherently-Enhanced Tunable Narrow-Band Terahertz Transition Radiation from a Relativistic Sub-Picosecond Electron Bunch Train
We experimentally demonstrate the production of narrow-band (% at THz) THz transition radiation with tunable
frequency over [0.37, 0.86] THz. The radiation is produced as a train of
sub-picosecond relativistic electron bunches transits at the vacuum-aluminum
interface of an aluminum converter screen. We also show a possible application
of modulated beams to extend the dynamical range of a popular bunch length
diagnostic technique based on the spectral analysis of coherent radiation.Comment: 3 pages, 6 figure
Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory
The main features in iron-pnictide superconductors are summarized as (i) the
orthorhombic transition accompanied by remarkable softening of shear modulus,
(ii) high-Tc superconductivity close to the orthorhombic phase, and (iii)
stripe-type magnetic order induced by orthorhombicity. To present a unified
explanation for them, we analyze the multiorbital Hubbard-Holstein model with
Fe-ion optical phonons based on the orbital fluctuation theory. In the
random-phase-approximation (RPA), a small electron-phonon coupling constant
() is enough to produce large orbital (=charge quadrupole)
fluctuations. The most divergent susceptibility is the
-antiferro-quadrupole (AFQ) susceptibility, which causes the s-wave
superconductivity without sign reversal (s_{++}-wave state). At the same time,
divergent development of -ferro-quadrupole (FQ) susceptibility is
brought by the "two-orbiton process" with respect to the AFQ fluctuations,
which is absent in the RPA. The derived FQ fluctuations cause the softening of
shear modulus, and its long-range-order not only triggers the
orthorhombic structure transition, but also induces the instability of
stripe-type antiferro-magnetic state. In other words, the condensation of
composite bosons made of two orbitons gives rise to the FQ order and structure
transition. The theoretically predicted multi-orbital-criticality presents a
unified explanation for abovementioned features of iron pnictide
superconductors.Comment: 19 pages, 15 figure
Vortex Origin of Tricritical Point in Ginzburg-Landau Theory
Motivated by recent experimental progress in the critical regime of
high- superconductors we show how the tricritical point in a
superconductor can be derived from the Ginzburg-Landau theory as a consequence
of vortex fluctuations. Our derivation explains why usual renormalization group
arguments always produce a first-order transition, in contrast to experimental
evidence and Monte Carlo simulations.Comment: 4 pages,1 figur
QCD and electroweak corrections to production in collision
We calculate the QCD and
electroweak one-loop corrections in the Standard Model framework, to the
production of an intermediate Higgs boson associated with pair via
fusion at an electron-positron linear collider (LC). We find
the QCD corrections can be larger than the electroweak ones, with the variations of the Higgs boson
mass and colliding energy . Both corrections may
significantly decrease or increase the Born cross section. The numerical
results show that the relative corrections from QCD to the process \eep may
reach 34.8%, when GeV and GeV, while those from
electroweak can be -13.1%, -15.8% and -12.0%, at GeV, 1 TeV
and 2 TeV respectively.Comment: 38 pages, 16 figure
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