655 research outputs found
Resonant production of the sterile neutrino dark matter and fine-tunings in the [nu]MSM
The generation of lepton asymmetry below the electroweak scale has a
considerable impact on production of dark matter sterile neutrinos.
Oscillations or decays of the heavier sterile neutrinos in the neutrino minimal
standard model can give rise to the requisite lepton asymmetry, provided the
masses of the heavier neutrinos are sufficiently degenerate. We study the
renormalization group evolution of the mass difference of these singlet
fermions to understand the degree of necessary fine-tuning. We construct an
example of the model that can lead to a technically natural realization of this
low-energy degeneracy.Comment: 8 pages, 5 figure
O(4) symmetric singular solutions and multiparticle cross sections in theory at tree level
We solve the classical euclidean boundary value problem for tree-level
multiparticle production in theory at arbitrary energies in the case
of symmetric field configurations. We reproduce known low-energy results
and obtain a lower bound on the tree cross sections at arbitrary energies.Comment: LaTeX, 9pp + 2 Postscript figures, tar-compressed and uuencoded using
uufiles; minor Postscript bug fixe
Compact extra-dimensions as solution to the strong CP problem
We show that the strong CP problem can, in principle, be solved dynamically
by adding extra-dimensions with compact topology. To this aim we consider a toy
model for QCD, which contains a vacuum angle and a strong CP like problem. We
further consider a higher dimensional theory, which has a trivial vacuum
structure and which reproduces the perturbative properties of the toy model in
the low-energy limit. In the weak coupling regime, where our computations are
valid, we show that the vacuum structure of the low-energy action is still
trivial and the strong CP problem is solved. No axion-like particle occur in
this setup and therefore it is not ruled out by astrophysical bounds.Comment: Discussion adde
Gauge singlet scalar as inflaton and thermal relic dark matter
We show that, by adding a gauge singlet scalar S to the standard model which
is nonminimally coupled to gravity, S can act both as the inflaton and as
thermal relic dark matter. We obtain the allowed region of the (m_s, m_h)
parameter space which gives a spectral index in agreement with observational
bounds and also produces the observed dark matter density while not violating
vacuum stability or nonperturbativity constraints. We show that, in contrast to
the case of Higgs inflation, once quantum corrections are included the spectral
index is significantly larger than the classical value (n = 0.966 for N = 60)
for all allowed values of the Higgs mass m_h. The range of Higgs mass
compatible with the constraints is 145 GeV < m_h < 170 GeV. The S mass lies in
the range 45 GeV < ms < 1 TeV for the case of a real S scalar with large
quartic self-coupling lambdas, with a smaller upper bound for smaller lambdas.
A region of the parameter space is accessible to direct searches at the LHC via
h-->SS, while future direct dark matter searches should be able to
significantly constrain the model.Comment: 13 pages, 7 figures. Published versio
On the Naturalness of Higgs Inflation
We critically examine the recent claim that the Standard Model Higgs boson
could drive inflation in agreement with observations if has a strong coupling to the Ricci curvature scalar. We
first show that the effective theory approach upon which that claim is based
ceases to be valid beyond a cutoff scale , where is the
reduced Planck mass. We then argue that knowing the Higgs potential profile for
the field values relevant for inflation () requires knowledge of the ultraviolet completion of the SM beyond
. In absence of such microscopic theory, the extrapolation of the pure
SM potential beyond is unwarranted and the scenario is akin to other
ad-hoc inflaton potentials afflicted with significant fine-tuning. The
appealing naturalness of this minimal proposal is therefore lost.Comment: 9 pages. Replaced with published version, plus a footnote clarifying
the use of power counting estimate
Magnetic field generation in Higgs inflation model
We study the generation of magnetic field in Higgs-inflation models where the
Standard Model Higgs boson has a large coupling to the Ricci scalar. We couple
the Higgs field to the Electromagnetic fields via a non- renormalizable
dimension six operator suppressed by the Planck scale in the Jordan frame. We
show that during Higgs inflation magnetic fields with present value
Gauss and comoving coherence length of can be generated in the
Einstein frame. The problem of large back-reaction which is generic in the
usual inflation models of magneto-genesis is avoided as the back-reaction is
suppressed by the large Higgs-curvature coupling.Comment: 10 pages, RevTeX
Circumventing the eta problem in building an inflationary model in string theory
The eta problem is one of the most significant obstacles to building a
successful inflationary model in string theory. Planck mass suppressed
corrections to the inflaton potential generally lead to inflaton masses of
order the Hubble scale and generate contributions of order unity to the eta
slow roll parameter rendering prolonged slow roll inflation impossible. We
demonstrate the severity of this problem in the context of brane anti-brane
inflation in a warped throat of a Calabi-Yau flux compactification with all
phenomenologically dangerous moduli stabilized. Using exact numerical solutions
we show that the eta problem can be avoided in scenarios where the inflaton is
non-minimally coupled to gravity and has Dirac-Born-Infeld (DBI) kinetic term.
We show that the resulting cosmic microwave background (CMB) observables such
as measures of non-gaussianites can, in principle, serve as a probe of
scalar-gravity couplings.Comment: 8 pages, 3 figures; title changed and reference added to match
published version in PR
Baryon Asymmetry of the Universe without Boltzmann or Kadanoff-Baym
We present a formalism that allows the computation of the baryon asymmetry of
the universe from first principles of statistical physics and quantum field
theory that is applicable to certain types of beyond the Standard Model physics
(such as the neutrino Minimal Standard Model -- MSM) and does not require
the solution of Boltzmann or Kadanoff-Baym equations. The formalism works if a
thermal bath of Standard Model particles is very weakly coupled to a new sector
(sterile neutrinos in the MSM case) that is out-of-equilibrium. The key
point that allows a computation without kinetic equations is that the number of
sterile neutrinos produced during the relevant cosmological period remains
small. In such a case, it is possible to expand the formal solution of the von
Neumann equation perturbatively and obtain a master formula for the lepton
asymmetry expressed in terms of non-equilibrium Wightman functions. The master
formula neatly separates CP-violating contributions from finite temperature
correlation functions and satisfies all three Sakharov conditions. These
correlation functions can then be evaluated perturbatively; the validity of the
perturbative expansion depends on the parameters of the model considered. Here
we choose a toy model (containing only two active and two sterile neutrinos) to
illustrate the use of the formalism, but it could be applied to other models.Comment: 26 pages, 10 figure
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