1,785 research outputs found
A String-Inspired Model for the Low- CMB
We present a semi--analytic exploration of some low-- angular power
spectra inspired by "Brane Supersymmetry Breaking". This mechanism splits Bose
and Fermi excitations in String Theory, leaving behind an exponential potential
that is just too steep for the inflaton to emerge from the initial singularity
while descending it. As a result, the scalar generically bounces against the
exponential wall, which typically introduces an infrared depression and a
pre--inflationary peak in the power spectrum of scalar perturbations. We
elaborate on a possible link between this phenomenon and the low-- CMB.
For the first 32 multipoles, combining the hard exponential with a milder one
leading to and with a small gaussian bump we have attained a
reduction of to about 46% of the standard CDM setting,
with both WMAP9 and PLANCK 2013 data. This result corresponds to a
of about 0.45, to be compared with a CDM value of
about 0.85. The preferred choices combine naturally quadrupole depression, a
first peak around and a wide minimum around . We have also
gathered some evidence that similar spectra emerge if the hard exponential is
combined with more realistic models of inflation. A problem of the preferred
examples is their slow convergence to an almost scale--invariant profile.Comment: 12 pages, latex, 7 figures. Power and limitations of the models and
of the semi-analytic approach stressed, misprints corrected. Final version to
appear in Mod. Phys. Lett.
Bound diquarks and their Bose-Einstein condensation in strongly coupled quark matter
We explore the formation of diquark molecules and their Bose-Einstein
condensation (BEC) in the phase diagram of three-flavor quark matter at nonzero
temperature, T, and quark chemical potential, mu. Using a quark model with a
four-fermion interaction, we identify possible diquark excitations as poles of
the microscopically computed diquark propagator. The quark masses are obtained
by solving a dynamical equation for the chiral condensate and are found to
determine the stability of the diquark excitations. The stability of diquark
excitations is investigated in the T-mu plane for different values of the
diquark coupling strength. We find that bound diquark molecules appear at small
quark chemical potentials at intermediate coupling and that BEC of non-strange
diquark molecules occurs if the attractive interaction between quarks is
sufficiently strong.Comment: 7 pages, 6 figure
Ground State Phase Diagram of S=1 XXZ Chains with Uniaxial Single-Ion-Type Anisotropy
One dimensional S=1 XXZ chains with uniaxial single-ion-type anisotropy are
studied by numerical exact diagonalization of finite size systems. The
numerical data are analyzed using conformal field theory, the level
spectroscopy, phenomenological renormalization group and finite size scaling
method. We thus present the first quantitatively reliable ground state phase
diagram of this model. The ground states of this model contain the Haldane
phase, large-D phase, N\'{e}el phase, two XY phases and the ferromagnetic
phase. There are four different types of transitions between these phases: the
Brezinskii-Kosterlitz-Thouless type transitions, the Gaussian type transitions,
the Ising type transitions and the first order transitions. The location of
these critical lines are accurately determined.Comment: 8 pages, 19 figure
Bose-Einstein condensation of diquark molecules in three-flavor quark matter
We study the phase diagram of strongly interacting matter with three quark
flavors at low and intermediate densities and non-zero temperatures in the
framework of an NJL-type model with four-point interactions. At large
densities, when the interactions are weak due to asymptotic freedom, quarks
form loosely bound Cooper pairs. However, when the density decreases,
interactions become stronger and quark Cooper pairs transform smoothly into
tightly bound diquark molecules. We find that such molecules are stable at low
density and temperature and that they dissociate above a temperature of the order of the chiral phase transition temperature
MeV. We also explore the conditions under which these molecules undergo
Bose-Einstein condensation (BEC). We find that BEC is only possible if we
increase the attractive interaction in the diquark channel to (probably
unrealistically) large values.Comment: 8 pages, 3 figures, proceedings of YKIS 2006 "New Frontiers in QCD
String Field Theory from IIB Matrix Model
We derive Schwinger-Dyson equations for the Wilson loops of a type IIB matrix
model. Superstring coordinates are introduced through the construction of the
loop space. We show that the continuum limit of the loop equation reproduces
the light-cone superstring field theory of type IIB superstring in the large-N
limit. We find that the interacting string theory can be obtained in the double
scaling limit as it is expected.Comment: 21 pages, Latex, 1 figur
Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain
We investigate the finite-field ground state of the S=1
antiferromagnetic-ferromagnetic bond-alternating chain described by the
Hamiltonian
{\calH}=\sum\nolimits_{\ell}\bigl\{\vecS_{2\ell-1}\cdot\vecS_{2\ell}
+J\vecS_{2\ell}\cdot\vecS_{2\ell+1}\bigr\} +D\sum\nolimits_{\ell}
\bigl(S_{\ell}^z)^2 -H\textstyle\sum\nolimits_\ell S_\ell^z, where
\hbox{} and \hbox{}. We find that two kinds of
magnetization plateaux at a half of the saturation magnetization, the
1/2-plateaux, appear in the ground-state magnetization curve; one of them is of
the Haldane type and the other is of the large--type. We determine the
1/2-plateau phase diagram on the versus plane, applying the
twisted-boundary-condition level spectroscopy methods developed by Kitazawa and
Nomura. We also calculate the ground-state magnetization curves and the
magnetization phase diagrams by means of the density-matrix
renormalization-group method
Pre-Inflationary Relics in the CMB?
String Theory and Supergravity allow, in principle, to follow the transition
of the inflaton from pre-inflationary fast roll to slow roll. This introduces
an infrared depression in the primordial power spectrum that might have left an
imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We
model the effect extending CDM with a scale related to the
infrared depression and explore the constraints allowed by {\sc Planck} data,
employing also more conservative, wider Galactic masks in the low resolution
CMB likelihood. In an extended mask with , we thus find \Delta =
(0.351 \pm 0.114) \times 10^{-3} \, \mbox{Mpc}^{-1}, at confidence
level, to be compared with a nearby value at with the standard
mask. With about 64 --folds of inflation, these values for
would translate into primordial energy scales GeV.Comment: 16 pages, 6 figures, 1 table. Final version to appear in Physics of
the Dark Universe. Contains: more detailed discussion of galactic masking,
improved estimat
BCS-BEC crossover in a relativistic superfluid and its significance to quark matter
The character change of a superfluid state due to the variation of the
attractive force is investigated in the relativistic framework with a massive
fermion. Two crossovers are found. One is a crossover from the usual BCS state
to the Bose-Einstein condensation (BEC) of bound fermion pairs. The other is
from the BEC to the relativistic Bose-Einstein condensation (RBEC) of nearly
massless bound pairs where antiparticles as well as particles dominate the
thermodynamics. Possible realization of the BEC and RBEC states in the quark
matter is also pointed out.Comment: 5 pages, 1 figure, revtex4; (v2) text has been clarified, references
updated; (v3) final version to appear in Phys. Rev.
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