208 research outputs found
Small cosmological constant in seesaw mechanism with breaking down SUSY
The observed small value of cosmological constant can be naturally related
with the scale of breaking down supersymmetry in agreement with other
evaluations in particle physics.Comment: 12 pages, revtex4 class, 2 eps-figure
Vacuum Decay on a Brane World
The bubble nucleation rate for a first order phase transition occurring on a
brane world is calculated. Both the Coleman-de Luccia thin wall instanton and
the Hawking-Moss instanton are considered. The results are compared with the
corresponding nucleation rates for standard four-dimensional gravity.Comment: 5 page
A Remark on Supersymmetric Bubbles and Spectrum Crossover
Using an exact expression for the domain wall tension in a supersymmetric
model we show that a spectrum crossover takes place in passing from weak to
strong coupling. In the weak coupling regime elementary excitations are the
lightest states, while in the strong coupling regime solitonic objects of a
special type -- bubbles -- assume the role of the lightest states. The
crossover occurs at \lambda^2/(4\pi) \sim 0.4.Comment: 6 p., 1 fi
The number of negative modes of the oscillating bounces
The spectrum of small perturbations about oscillating bounce solutions
recently discussed in the literature is investigated. Our study supports quite
intuitive and expected result: the bounce with N nodes has exactly N
homogeneous negative modes. Existence of more than one negative modes makes
obscure the relation of these oscillating bounce solutions to the false vacuum
decay processes.Comment: LaTex, 6 pages, including 3 figure
Cosmological constant in scale-invariant theories
The incorporation of a small cosmological constant within radiatively-broken
scale-invariant models is discussed. We show that phenomenologically consistent
scale-invariant models can be constructed which allow a small positive
cosmological constant, providing certain relation between the particle masses
is satisfied. As a result, the mass of the dilaton is generated at two-loop
level. Another interesting consequence is that the electroweak
symmetry-breaking vacuum in such models is necessarily a metastable `false'
vacuum which, fortunately, is not expected to decay on cosmological time
scales.Comment: 10 pages; v2: clarifying remarks added, to appear in Physical Review
Effects of quarks on the formation and evolution of Z(3) walls and strings in relativistic heavy-ion collisions
We investigate the effects of explicit breaking of Z(3) symmetry due to the
presence of dynamical quarks on the formation and evolution of Z(3) walls and
associated QGP strings within Polyakov loop model. We carry out numerical
simulations of the first order quark-hadron phase transition via bubble
nucleation (which may be appropriate, for example, at finite baryon chemical
potential) in the context of relativistic heavy-ion collision experiments.
Using appropriate shifting of the order parameter in the Polyakov loop
effective potential, we calculate the bubble profiles using bounce technique,
for the true vacuum as well as for the metastable Z(3) vacua, and estimate the
associated nucleation probabilities. These different bubbles are then nucleated
and evolved and resulting formation and dynamics of Z(3) walls and QGP strings
is studied. We discuss various implications of the existence of these Z(3)
interfaces and the QGP strings, especially in view of the effects of the
explicit breaking of the Z(3) symmetry on the formation and dynamical evolution
of these objects.Comment: 17 pages, 9 figures, PDFLate
The Twin Higgs: Natural Electroweak Breaking from Mirror Symmetry
We present `twin Higgs models', simple realizations of the Higgs as a
pseudo-Goldstone boson that protect the weak scale from radiative corrections
up to scales of order 5 - 10 TeV. In the ultra-violet these theories have a
discrete symmetry which interchanges each Standard Model particle with a
corresponding particle which transforms under a twin or mirror Standard Model
gauge group. In addition, the Higgs sector respects an approximate global SU(4)
symmetry. When this global symmetry is broken, the discrete symmetry tightly
constrains the form of corrections to the pseudo-Goldstone Higgs potential,
allowing natural electroweak symmetry breaking. Precision electroweak
constraints are satisfied by construction. These models demonstrate that,
contrary to the conventional wisdom, stabilizing the weak scale does not
require new light particles charged under the Standard Model gauge groups.Comment: 5 pages. Updated to the journal versio
Where are the Walls?
The reported spatial variation in the fine-structure constant at high
redshift, if physical, could be due to the presence of dilatonic domains, and
one or more domain walls inside our horizon. An absorption spectrum of an
object in a different domain from our own would be characterized by a different
value of alpha. We show that while a single wall solution is statically
comparable to a dipole fit, and is a big improvement over a weighted mean
(despite adding 3 parameters), a two-wall solution is a far better fit (despite
adding 3 parameters over the single wall solution). We derive a simple model
accounting for the two-domain wall solution. The goodness of these fits is
however dependent on the extra random error which was argued to account for the
large scatter in most of the data. When this error is omitted, all the above
solutions are poor fits to the data. When included, the solutions that exhibit
a spatial dependence agree with the data much more significantly than the
Standard Model; however, the Standard Model itself is not a terrible fit to the
data, having a p-value of ~ 20 %
Gravitational corrections to Standard Model vacuum decay
We refine and update the metastability constraint on the Standard Model top
and Higgs masses, by analytically including gravitational corrections to the
vacuum decay rate. Present best-fit ranges of the top and Higgs masses mostly
lie in the narrow metastable region. Furthermore, we show that the SM potential
can be fine-tuned in order to be made suitable for inflation. However, SM
inflation results in a power spectrum of cosmological perturbations not
consistent with observations.Comment: 8 pages, 4 figure
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