199 research outputs found
Domain Walls in SU(5)
We consider the Grand Unified SU(5) model with a small or vanishing cubic
term in the adjoint scalar field in the potential. This gives the model an
approximate or exact Z symmetry whose breaking leads to domain walls. The
simplest domain wall has the structure of a kink across which the Higgs field
changes sign () and inside which the full SU(5) is restored.
The kink is shown to be perturbatively unstable for all parameters. We then
construct a domain wall solution that is lighter than the kink and show it to
be perturbatively stable for a range of parameters. The symmetry in the core of
this domain wall is smaller than that outside. The interactions of the domain
wall with magnetic monopole is discussed and it is shown that magnetic
monopoles with certain internal space orientations relative to the wall pass
through the domain wall. Magnetic monopoles in other relative internal space
orientations are likely to be swept away on collision with the domain walls,
suggesting a scenario where the domain walls might act like optical
polarization filters, allowing certain monopole ``polarizations'' to pass
through but not others. As SU(5) domain walls will also be formed at small
values of the cubic coupling, this leads to a very complicated picture of the
evolution of defects after the Grand Unified phase transition.Comment: 6 pages, 1 figure. Animations can be viewed at
http://theory4.phys.cwru.edu/~levon/figures.htm
Probing Primordial Magnetism with Off-Diagonal Correlators of CMB Polarization
Primordial magnetic fields (PMF) can create polarization -modes in the
cosmic microwave background (CMB) through Faraday rotation (FR), leading to
non-trivial 2-point and 4-point correlators of the CMB temperature and
polarization. We discuss the detectability of primordial magnetic fields using
different correlators and evaluate their relative merits. We have fully
accounted for the contamination by weak lensing, which contributes to the
variance, but whose contribution to the 4-point correlations is orthogonal to
that of FR. We show that a Planck-like experiment can detect scale-invariant
PMF of nG strength using the FR diagnostic at 90GHz, while realistic future
experiments at the same frequency can detect 10^{-10} G. Utilizing multiple
frequencies will improve on these prospects, making FR of CMB a powerful probe
of scale-invariant PMF.Comment: 11 pages, 4 figures; unit typos fixed in fig 1 and
Dynamics of the infinitely-thin kink
We consider the dynamics of the domain-wall kink soliton, in particular we
study the zero mode of translation. In the infinitely-thin kink limit, we show
that the zero mode is almost completely frozen out, the only remnant being a
dynamically constrained four-dimensional mode of a single but arbitrary
frequency. In relation to this result, we show that the usual mode expansion
for dealing with zero modes -- implicit collective coordinates -- is not in
fact a completely general expansion, and that one must use instead a
traditional generalised Fourier analysis.Comment: 13 pages; v2: added references, to appear in Phys Lett
Kink interactions in
There are classes of kink solutions in . We show how
interactions between various kinks depend on the classes of individual kinks as
well as on their orientations with respect to each other in the internal space.
In particular, we find that the attractive or repulsive nature of the
interaction depends on the trace of the product of charges of the two kinks. We
calculate the interaction potential for all combinations of kinks and antikinks
in and study their collisions. The outcome of kink-antikink
collisions, as expected from previous studies, is sensitive to their initial
relative velocity. We find that heavier kinks tend to break up into lighter
ones, while interactions between the lightest kinks and antikinks in this model
can be repulsive as well as attractive.Comment: 11 pages, 9 figures. Two insignificant sign errors corrected in the
revised versio
Space of kink solutions in SU(N)\times Z_2
We find distinct classes (``generations'') of kink solutions in an
field theory. The classes are labeled by an integer . The
members of one class of kinks will be globally stable while those of the other
classes may be locally stable or unstable. The kink solutions in the
class have a continuous degeneracy given by the manifold ,
where is the unbroken symmetry group and is the group under which the
kink solution remains invariant. The space is found to contain
incontractable two spheres for some values of , indicating the possible
existence of certain incontractable spherical structures in three dimensions.
We explicitly construct the three classes of kinks in an SU(5) model with
quartic potential and discuss the extension of these ideas to magnetic monopole
solutions in the model.Comment: 11 pages, 3 figures. Several minor changes made. Matches the version
accepted to PR
Scaling configurations of cosmic superstring networks and their cosmological implications
We study the cosmic microwave background temperature and polarisation spectra
sourced by multi-tension cosmic superstring networks. First we obtain solutions
for the characteristic length scales and velocities associated with the
evolution of a network of F-D strings, allowing for the formation of junctions
between strings of different tensions. We find two distinct regimes describing
the resulting scaling distributions for the relative densities of the different
types of strings, depending on the magnitude of the fundamental string coupling
g_s. In one of them, corresponding to the value of the coupling being of order
unity, the network's stress-energy power spectrum is dominated by populous
light F and D strings, while the other regime, at smaller values of g_s, has
the spectrum dominated by rare heavy D strings. These regimes are seen in the
CMB anisotropies associated with the network. We focus on the dependence of the
shape of the B-mode polarisation spectrum on g_s and show that measuring the
peak position of the B-mode spectrum can point to a particular value of the
string coupling. Finally, we assess how this result, along with pulsar bounds
on the production of gravitational waves from strings, can be used to constrain
a combination of g_s and the fundamental string tension mu_F. Since CMB and
pulsar bounds constrain different combinations of the string tensions and
densities, they result in distinct shapes of bounding contours in the (mu_F,
g_s) parameter plane, thus providing complementary constraints on the
properties of cosmic superstrings.Comment: 23 pages, 8 figures, 3 tables; V2: matches published version (PRD
A Note on the evolution of cosmic string/superstring networks
In the context of brane world scenario, cosmic superstrings can be formed in
D-brane annihilation at the end of the brane inflationary era. The cosmic
superstring network has a scaling solution and the characteristic scale of the
network is proportional to the square root of the reconnection probability.Comment: 13 pages, 12 figures (revised version
B-modes from Cosmic Strings
Detecting the parity-odd, or B-mode, polarization pattern in the cosmic
microwave background radiation due to primordial gravity waves is considered to
be the final observational key to confirming the inflationary paradigm. The
search for viable models of inflation from particle physics and string theory
has (re)discovered another source for B-modes: cosmic strings. Strings
naturally generate as much vector mode perturbation as they do scalar,
producing B-mode polarization with a spectrum distinct from that expected from
inflation itself. In a large set of models, B-modes arising from cosmic strings
are more prominent than those expected from primordial gravity waves. In light
of this, we study the physical underpinnings of string-sourced B-modes and the
model dependence of the amplitude and shape of the power spectrum.
Observational detection of a string-sourced B-mode spectrum would be a direct
probe of post-inflationary physics near the GUT scale. Conversely,
non-detection would put an upper limit on a possible cosmic string tension of
G\mu < 10^{-7} within the next three years.Comment: 13 pages, 5 figures; v3: minor corrections made following referee
comments, plus extra discussion and figures added after receiving feedbac
Cosmic strings and Natural Inflation
In the present work we discuss cosmic strings in natural inflation. Our
analysis is based entirely on the CMB quadrupole temperature anisotropy and on
the existing upper bound on the cosmic string tension. Our results show that
the allowed range for both parameters of the inflationary model is very
different from the range obtained recently if cosmic strings are formed at the
same time with inflation, while if strings are formed after inflation we find
that the parameters of the inflationary model are similar to the ones obtained
recently.Comment: 12 pages, 0 tables, 4 figures, accepted for publication in JHE
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