316 research outputs found
Entropy production in the early-cosmology pionic phase
We point out that in the early universe, for temperatures in the approximate
interval 175-80 MeV (after the quark-gluon plasma), pions carried a large share
of the entropy and supported the largest inhomogeneities. Thus, we examine the
production of entropy in a pion gas, particularizing to inhomogeneities of the
temperature, for which we benefit from the known thermal conductivity. We
finally put that entropy produced in relaxing such thermal inhomogeneities in
the broad context of this relatively unexplored phase of early-universe
cosmology.Comment: 10 pages, 10 figures
Coupling WW, ZZ unitarized amplitudes to in the TeV region
We define and calculate helicity partial-wave amplitudes for processes
linking the Electroweak Symmetry Breaking Sector (EWSBS) to ,
employing (to NLO) the Higgs-EFT (HEFT) extension of the Standard Model and the
Equivalence Theorem, while neglecting all particle masses. The resulting
amplitudes can be useful in the energy regime ().
We also deal with their unitarization so that resonances of the EWSBS can
simultaneously be described in the initial or final states. Our
resulting amplitudes satisfy unitarity, perturbatively in , but for all
values. In this way we improve on the HEFT that fails as interactions
become stronger with growing and provide a natural framework for the decay
of dynamically generated resonances into , and pairs.Comment: 23 pages, 9 figure
Production cross section estimates for strongly-interacting Electroweak Symmetry Breaking Sector resonances at particle colliders
We are exploring a generic strongly-interacting Electroweak Symmetry Breaking
Sector (EWSBS) with the low-energy effectie field theory for the four
experimentally known particles (, , ) and its
dispersion-relation based unitary extension. In this contribution we provide
simple estimates for the production cross section of pairs of the EWSBS bosons
and their resonances at proton-proton colliders as well as in a future
(or potentially a ) collider with a typical few-TeV energy. We
examine the simplest production mechanisms, tree-level production through a
(dominant when quantum numbers allow) and the simple effective boson
approximation (in which the electroweak bosons are considered as collinear
partons of the colliding fermions). We exemplify with custodial isovector and
isotensor resonances at 2 TeV, the energy currently being discussed because of
a slight excess in the ATLAS 2-jet data. We find it hard, though not
unthinkable, to ascribe this excess to one of these rescattering
resonances. An isovector resonance could be produced at a rate smaller than,
but close to earlier CMS exclusion bounds, depending on the parameters of the
effective theory. The excess is then problematic and requires additional
physics (such as an additional scalar resonance). The isotensor one (that would
describe all charge combinations) has a smaller cross section.Comment: 15 pages, 8 figure
Possible new resonance from - interchannel coupling
We propose and theoretically study a possible new resonance caused by strong
coupling between the Higgs-Higgs and the W_L W_L (Z_L Z_L) scattering channels,
without regard to the intensity of the elastic interaction in either channel at
low energy (that could be weak as in the Standard Model). We expose this
channel-coupling resonance from unitarity and dispersion relations encoded in
the Inverse Amplitude Method, applied to the Electroweak Chiral Lagrangian with
a scalar Higgs.Comment: 4 pages, 7 figure
Unitarity, analyticity, dispersion relations and resonances in strongly interacting , and scattering
If the Electroweak Symmetry Breaking Sector turns out to be strongly
interacting, the actively investigated effective theory for longitudinal gauge
bosons plus Higgs can be efficiently extended to cover the regime of saturation
of unitarity (where the perturbative expansion breaks down). This is achieved
by dispersion relations, whose subtraction constants and left cut contribution
can be approximately obtained in different ways giving rise to different
unitarization procedures. We illustrate the ideas with the Inverse Amplitude
Method, one version of the N/D method and another improved version of the
K-matrix. In the three cases we get partial waves which are unitary, analytical
with the proper left and right cuts and in some cases poles in the second
Riemann sheet that can be understood as dynamically generated resonances. In
addition they reproduce at Next to Leading Order (NLO) the perturbative
expansion for the five partial waves not vanishing (up to J=2) and they are
renormalization scale () independent. Also the unitarization formalisms
are extended to the coupled channel case. Then we apply the results to the
elastic scattering amplitude for the longitudinal components of the gauge
bosons at high energy. We also compute and the
inelastic process which are coupled to the elastic
channel for custodial isospin . We numerically compare the three methods
for various values of the low-energy couplings and explain the reasons for the
differences found in the partial wave. Then we study the resonances
appearing in the different elastic and coupled channels in terms of the
effective Lagrangian parameters.Comment: 45 pages, 28 figure
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