144 research outputs found
Centre-of-mass separation in quantum mechanics: Implications for the many-body treatment in quantum chemistry and solid state physics
We address the question to what extent the centre-of-mass (COM) separation
can change our view of the many-body problem in quantum chemistry and solid
state physics. It was shown that the many-body treatment based on the
electron-vibrational Hamiltonian is fundamentally inconsistent with the
Born-Handy ansatz so that such a treatment can never respect the COM problem.
Born-Oppenheimer (B-O) approximation reveals some secret: it is a limit case
where the degrees of freedom can be treated in a classical way. Beyond the B-O
approximation they are inseparable in principle. The unique covariant
description of all equations with respect to individual degrees of freedom
leads to new types of interaction: besides the known vibronic (electron-phonon)
one the rotonic (electron-roton) and translonic (electron-translon)
interactions arise. We have proved that due to the COM problem only the
hypervibrations (hyperphonons, i.e. phonons + rotons + translons) have true
physical meaning in molecules and crystals; nevertheless, the use of pure
vibrations (phonons) is justified only in the adiabatic systems. This fact
calls for the total revision of our contemporary knowledge of all non-adiabatic
effects, especially the Jahn-Teller effect and superconductivity. The vibronic
coupling is responsible only for removing of electron (quasi)degeneracies but
for the explanation of symmetry breaking and forming of structure the rotonic
and translonic coupling is necessary.Comment: 39 pages, 11 sections, 3 appendice
Natural Warm Inflation
We derive the requirements that a generic axion-like field has to satisfy in
order to play the role of the inflaton field in the warm inflation scenario.
Compared to the parameter space in ordinary natural inflation models, we find
that the parameter space in our model is enlarged. In particular, we avoid the
problem of having an axion decay constant that relates to the Planck scale,
which is instead present in the ordinary natural inflation models; in fact, our
model can easily accommodate values of the axion decay constant that lie well
below the Planck scale.Comment: 19 pages, 7 figures; version accepted in JCA
Isocurvature forecast in the anthropic axion window
We explore the cosmological sensitivity to the amplitude of isocurvature
fluctuations that would be caused by axions in the "anthropic window" where the
axion decay constant f_a >> 10^12 GeV and the initial misalignment angle
Theta_i << 1. In a minimal Lambda-CDM cosmology extended with subdominant
scale-invariant isocurvature fluctuations, existing data constrain the
isocurvature fraction to alpha < 0.09 at 95% C.L. If no signal shows up, Planck
can improve this constraint to 0.042 while an ultimate CMB probe limited only
by cosmic variance in both temperature and E-polarisation can reach 0.017,
about a factor of five better than the current limit. In the parameter space of
f_a and H_I (Hubble parameter during inflation) we identify a small region
where axion detection remains within the reach of realistic cosmological
probes.Comment: 14 pages, 4 figures; v2: matches published versio
Stochastic conversions of TeV photons into axion-like particles in extragalactic magnetic fields
Very-high energy photons emitted by distant cosmic sources are absorbed on
the extragalactic background light (EBL) during their propagation. This effect
can be characterized in terms of a photon transfer function at Earth. The
presence of extragalactic magnetic fields could also induce conversions between
very high-energy photons and hypothetical axion-like particles (ALPs). The
turbulent structure of the extragalactic magnetic fields would produce a
stochastic behaviour in these conversions, leading to a statistical
distribution of the photon transfer functions for the different realizations of
the random magnetic fields. To characterize this effect, we derive new
equations to calculate the mean and the variance of this distribution. We find
that, in presence of ALP conversions, the photon transfer functions on
different lines of sight could have relevant deviations with respect to the
mean value, producing both an enhancement or a suppression in the observable
photon flux with respect to the expectations with only absorption. As a
consequence, the most striking signature of the mixing with ALPs would be a
reconstructed EBL density from TeV photon observations which appears to vary
over different directions of the sky: consistent with standard expectations in
some regions, but inconsistent in others.Comment: v2: 22 pages, 5 eps figures. Minor changes. A reference added.
Matches the version published on JCA
Axionic dark energy and a composite QCD axion
We discuss the idea that the model-independent (MI) axion of string theory is
the source of quintessential dark energy. The scenario is completed with a
composite QCD axion from hidden sector squark condensation that could serve as
dark matter candidate. The mechanism relies on the fact that the hidden sector
anomaly contribution to the composite axion is much smaller than the QCD
anomaly term. This intuitively surprising scenario is based on the fact that
below the hidden sector scale there are many light hidden sector
quarks. Simply, by counting engineering dimensions the hidden sector instanton
potential can be made negligible compared to the QCD anomaly term.Comment: 9 pages, 7 figure
Quark mass uncertainties revive KSVZ axion dark matter
The Kaplan-Manohar ambiguity in light quark masses allows for a larger
uncertainty in the ratio of up to down quark masses than naive estimates from
the chiral Lagrangian would indicate. We show that it allows for a relaxation
of experimental bounds on the QCD axion, specifically KSVZ axions in the eV mass range composing 100% of the galactic dark matter halo can evade the
experimental limits placed by the ADMX collaboration.Comment: 9 pages, 5 figure
Axion-like particle effects on the polarization of cosmic high-energy gamma sources
Various satellite-borne missions are being planned whose goal is to measure
the polarization of a large number of gamma-ray bursts (GRBs). We show that the
polarization pattern predicted by current models of GRB emission can be
drastically modified by the existence of very light axion-like particles
(ALPs), which are present in many extensions of the Standard Model of particle
physics. Basically, the propagation of photons emitted by a GRB through cosmic
magnetic fields with a domain-like structure induces photon-ALP mixing, which
is expected to produce a strong modification of the original photon
polarization. Because of the random orientation of the magnetic field in each
domain, this effect strongly depends on the orientation of the photon line of
sight. As a consequence, photon-ALP conversion considerably broadens the
original polarization distribution. Searching for such a peculiar feature
through future high-statistics polarimetric measurements is therefore a new
opportunity to discover very light ALPs.Comment: Final version (21 pages, 8 eps figures). Matches the version
published on JCAP. Added a Section on the effects of cosmic expansion on
photon-ALP conversions. Figures modified to take into account this effect.
References updated. Conclusions unchanged
Mixed axion/neutralino cold dark matter in supersymmetric models
We consider supersymmetric (SUSY) models wherein the strong CP problem is
solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino
supermultiplet. We examine R-parity conserving models where the neutralino is
the lightest SUSY particle, so that a mixture of neutralinos and axions serve
as cold dark matter. The mixed axion/neutralino CDM scenario can match the
measured dark matter abundance for SUSY models which typically give too low a
value of the usual thermal neutralino abundance, such as models with wino-like
or higgsino-like dark matter. The usual thermal neutralino abundance can be
greatly enhanced by the decay of thermally-produced axinos to neutralinos,
followed by neutralino re-annihilation at temperatures much lower than
freeze-out. In this case, the relic density is usually neutralino dominated,
and goes as \sim (f_a/N)/m_{axino}^{3/2}. If axino decay occurs before
neutralino freeze-out, then instead the neutralino abundance can be augmented
by relic axions to match the measured abundance. Entropy production from
late-time axino decays can diminish the axion abundance, but ultimately not the
neutralino abundance. In mixed axion/neutralino CDM models, it may be possible
to detect both a WIMP and an axion as dark matter relics. We also discuss
possible modifications of our results due to production and decay of saxions.
In the appendices, we present expressions for the Hubble expansion rate and the
axion and neutralino relic densities in radiation, matter and decaying-particle
dominated universes.Comment: 31 pages including 21 figure
F-theory, GUTs, and the Weak Scale
In this paper we study a deformation of gauge mediated supersymmetry breaking
in a class of local F-theory GUT models where the scale of supersymmetry
breaking determines the value of the mu term. Geometrically correlating these
two scales constrains the soft SUSY breaking parameters of the MSSM. In this
scenario, the hidden SUSY breaking sector involves an anomalous U(1)
Peccei-Quinn symmetry which forbids bare mu and B mu terms. This sector
typically breaks supersymmetry at the desired range of energy scales through a
simple stringy hybrid of a Fayet and Polonyi model. A variant of the
Giudice-Masiero mechanism generates the value mu ~ 10^2 - 10^3 GeV when the
hidden sector scale of supersymmetry breaking is F^(1/2) ~ 10^(8.5) GeV.
Further, the B mu problem is solved due to the mild hierarchy between the GUT
scale and Planck scale. These models relate SUSY breaking with the QCD axion,
and solve the strong CP problem through an axion with decay constant f_a ~
M_(GUT) * mu / L, where L ~ 10^5 GeV is the characteristic scale of gaugino
mass unification in gauge mediated models, and the ratio \mu / L ~
M_(GUT)/M_(pl) ~ 10^(-3). We find f_a ~ 10^12 GeV, which is near the high end
of the phenomenologically viable window. Here, the axino is the goldstino mode
which is eaten by the gravitino. The gravitino is the LSP with a mass of about
10^1 - 10^2 MeV, and a bino-like neutralino is (typically) the NLSP with mass
of about 10^2 - 10^3 GeV. Compatibility with electroweak symmetry breaking also
determines the value of tan(beta) ~ 30 +/- 7.Comment: v3: 94 pages, 9 figures, clarification of Fayet-Polonyi model and
instanton corrections to axion potentia
Constraints on the CMB temperature redshift dependence from SZ and distance measurements
The relation between redshift and the CMB temperature,
is a key prediction of standard cosmology, but is violated in many non-standard
models. Constraining possible deviations to this law is an effective way to
test the CDM paradigm and search for hints of new physics. We present
state-of-the-art constraints, using both direct and indirect measurements. In
particular, we point out that in models where photons can be created or
destroyed, not only does the temperature-redshift relation change, but so does
the distance duality relation, and these departures from the standard behaviour
are related, providing us with an opportunity to improve constraints. We show
that current datasets limit possible deviations of the form
to be up to a redshift
. We also discuss how, with the next generation of space and
ground-based experiments, these constraints can be improved by more than one
order of magnitude.Comment: 27 pages, 11 figure
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