80 research outputs found
The Gravitational Wave Background and Higgs False Vacuum Inflation
For a narrow band of values of the top quark and Higgs boson masses, the
Standard Model Higgs potential develops a shallow local minimum at energies of
about GeV, where primordial inflation could have started in a cold
metastable state. For each point of that band, the highness of the Higgs
potential at the false minimum is calculable, and there is an associated
prediction for the inflationary gravitational wave background, namely for the
tensor to scalar ratio . We show that the recent measurement of by the
BICEP2 collaboration, at , combined with the
most up-to-date measurements of the top quark and Higgs boson masses, reveals
that the hypothesis that a Standard Model shallow false minimum was the source
of inflation in the early Universe is viable.Comment: 4 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1112.543
Higgs boson and Top quark masses as tests of Electroweak Vacuum Stability
The measurements of the Higgs boson and top quark masses can be used to
extrapolate the Standard Model Higgs potential at energies up to the Planck
scale. Adopting a NNLO renormalization procedure, we: i) find that electroweak
vacuum stability is at present allowed, discuss the associated theoretical and
experimental errors and the prospects for its future tests; ii) determine the
boundary conditions allowing for the existence of a shallow false minimum
slightly below the Planck scale, which is a stable configuration that might
have been relevant for primordial inflation; iii) derive a conservative upper
bound on type I seesaw right-handed neutrino masses, following from the
requirement of electroweak vacuum stability.Comment: v1: 22 pages, 9 figures; v2: 26 pages, 11 figures: improved text,
added detailed comparison with previous literature results, version matching
the PRD articl
The Higgs mass range from Standard Model false vacuum Inflation in scalar-tensor gravity
If the Standard Model is valid up to very high energies it is known that the
Higgs potential can develop a local minimum at field values around
GeV, for a narrow band of values of the top quark and Higgs
masses. We show that in a scalar-tensor theory of gravity such Higgs false
vacuum can give rise to viable inflation if the potential barrier is very
shallow, allowing for tunneling and relaxation into the electroweak scale true
vacuum. The amplitude of cosmological density perturbations from inflation is
directly linked to the value of the Higgs potential at the false minimum.
Requiring the top quark mass, the amplitude and spectral index of density
perturbations to be compatible with observations, selects a narrow range of
values for the Higgs mass, GeV, where the error is mostly
due to the theoretical uncertainty of the 2-loop RGE. This prediction could be
soon tested at the Large Hadron Collider. Our inflationary scenario could also
be further checked by better constraining the spectral index and the
tensor-to-scalar ratio.Comment: v1: 14 pages, 4 figures; v2: 18 pages, 8 figures, text improved, new
section and figures adde
Stationary configurations of the Standard Model Higgs potential: electroweak stability and rising inflection point
We study the gauge-independent observables associated with two interesting
stationary configurations of the Standard Model Higgs potential (extrapolated
to high energy according to the present state of the art, namely the NNLO): i)
the value of the top mass ensuring stability of the SM electroweak minimum, and
ii) the value of the Higgs potential at a rising inflection point. We examine
in detail and reappraise the experimental and theoretical uncertainties which
plague their determination, finding that: i) stability of the SM is compatible
with the present data at the 1.5 sigma level; ii) despite the large theoretical
error plaguing the value of the Higgs potential at a rising inflection point,
application of such configuration to models of primordial inflation displays a
3 sigma tension with the recent bounds on the tensor-to-scalar ratio of
cosmological perturbations.Comment: v1: 21 pages, 6 figures; v2: 22 pages, 7 figures, text improved,
figure and references added, matches published versio
Ruling out Critical Higgs Inflation?
We consider critical Higgs inflation, namely Higgs inflation with a rising
inflection point at smaller field values than those of the plateau induced by
the non-minimal coupling to gravity. It has been proposed that such
configuration is compatible with the present CMB observational constraints on
inflation, and also with primordial black hole production accounting for the
totality or a fraction of the observed dark matter. We study the model taking
into account the NNLO corrections to the Higgs effective potential: such
corrections are extremely important to reduce the theoretical error associated
to the calculation. We find that, in the 3 sigma window for the relevant low
energy parameters, which are the strong coupling and the Higgs mass (the top
mass follows by requiring an inflection point), the potential at the inflection
point is so large (and so is the Hubble constant during inflation) that the
present bound on the tensor-to-scalar ratio is violated. The model is viable
only allowing the strong coupling to take its upper 3-4 sigma value. In our
opinion, this tension shows that the model of critical Higgs inflation is
likely to be not viable: neither inflation nor black holes as dark matter can
be originated in this version of the model.Comment: v1: 21 pages, 5 figures; v2: 23 pages, 5 figures, improved text and
figures, results unchange
The problem of neutrino masses in extensions of the Standard Model
We review the problem of neutrino masses and mixings in the context of Grand
Unified Theories. After a brief summary of the present experimental status of
neutrino physics, we describe how the see-saw mechanism can automatically
account for the large atmospheric mixing angle. We provide two specific
examples where this possibility is realized by means of a flavour symmetry. We
then review in some detail the various severe problems which plague minimal GUT
models (like the doublet-triplet splitting and proton-decay) and which force to
investigate the possibility of constructing more elaborate but realistic
models. We then show an example of a quasi-realistic SUSY SU(5) model which, by
exploiting the crucial presence of an abelian flavour symmetry, does not
require any fine-tuning and predicts a satisfactory phenomenology with respect
to coupling unification, fermion masses and mixings and bounds from proton
decay.Comment: 140 pages, 6 figures; based on PhD thesis work; accepted by Int.
Jour. of Mod. Phys.
Electroweak vacuum stability and finite quadratic radiative corrections
If the Standard Model (SM) is an effective theory, as currently believed, it
is valid up to some energy scale to which the Higgs vacuum
expectation value is sensitive throughout radiative quadratic terms. The latter
ones destabilize the electroweak vacuum and generate the SM hierarchy problem.
For a given perturbative Ultraviolet (UV) completion, the SM cutoff can be
computed in terms of fundamental parameters. If the UV mass spectrum involves
several scales the cutoff is not unique and each SM sector has its own UV
cutoff . We have performed this calculation assuming the Minimal
Supersymmetric Standard Model (MSSM) is the SM UV completion. As a result, from
the SM point of view, the quadratic corrections to the Higgs mass are
equivalent to finite threshold contributions. For the measured values of the
top quark and Higgs masses, and depending on the values of the different
cutoffs , these contributions can cancel even at renormalization
scales as low as multi-TeV, unlike the case of a single cutoff where the
cancellation only occurs at Planckian energies, a result originally obtained by
Veltman. From the MSSM point of view, the requirement of stability of the
electroweak minimum under radiative corrections is incorporated into the
matching conditions and provides an extra constraint on the Focus Point
solution to the little hierarchy problem in the MSSM. These matching conditions
can be employed for precise calculations of the Higgs sector in scenarios with
heavy supersymmetric fields.Comment: 36 pages, 5 figures; v2: logarithm corrections included, figures
improved, references adde
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