36 research outputs found
Extra Higgs bosons in ttbar production at the LHC
The top quark has a large Yukawa coupling with the Higgs boson. In the usual
extensions of the standard model the Higgs sector includes extra scalars, which
also tend to couple strongly with the top quark. Unlike the Higgs, these fields
have a natural mass above 2m_t, so they could introduce anomalies in ttbar
production at the LHC. We study their effect on the ttbar invariant mass
distribution at sqrt{s}=7 TeV. We focus on the bosons (H,A) of the minimal SUSY
model and on the scalar field (r) associated to the new scale f in Little Higgs
(LH) models. We show that in all cases the interference with the standard
amplitude dominates over the narrow-width contribution. As a consequence, the
mass difference between H and A or the contribution of an extra T-quark loop in
LH models become important effects in order to determine if these fields are
observable there. We find that a 1 fb^{-1} luminosity could probe the region
tan beta \le 3 of SUSY and v/(sqrt{2}f) \ge 0.3 in LH models.Comment: 18 pages, version to appear in PR
A minimal Little Higgs model
We discuss a Little Higgs scenario that introduces below the TeV scale just
the two minimal ingredients of these models, a vectorlike T quark and a singlet
component (implying anomalous couplings) in the Higgs field, together with a
pseudoscalar singlet \eta. In the model, which is a variation of Schmaltz's
simplest Little Higgs model, all the extra vector bosons are much heavier than
the T quark. In the Yukawa sector the global symmetry is approximate, implying
a single large coupling per flavour, whereas in the scalar sector it is only
broken at the loop level. We obtain the one-loop effective potential and show
that it provides acceptable masses for the Higgs h and for the singlet \eta
with no need for an extra \mu term. We find that m_\eta can be larger than
m_h/2, which would forbid the (otherwise dominant) decay mode h -> \eta\eta.Comment: 16 pages. References added, fine tuning analysis included. Version to
appear in PR
The Higgs Boson and New Physics at the TeV Scale
In this Thesis two different parts can be distinguished. In the first one,
after a review of the SM Higgs sector, I describe some scenarios for new
physics such as Little Higgs and Supersymmetry and discuss our contributions in
each of them. In the second part I focus on one of the most interesting
experimental hints of new physics, the forward-backward asymmetry in top-pair
production measured at the Tevatron, analyzing in detail its possible
implications at the LHC.Comment: Ph.D. Thesis, Universidad de Granada, March 2012, 129 page
Gluon excitations in t tbar production at hadron colliders
We argue that a relatively light massive gluon with mass <= 1 TeV, small
purely axial couplings to light quarks and sizable vector and axial couplings
to the top quark can reproduce the large forward-backward asymmetry observed at
the Tevatron without conflicting with the t tbar and the dijet invariant mass
distributions measured at the Tevatron and the LHC. We show that realistic
Higgsless models with warped extra dimensions naturally fulfil all the
necessary ingredients to realize this scenario. While current data is unable to
discover or exclude these heavy gluons with masses 850 GeV, they should be
observed at the (7 TeV) LHC with a luminosity of the order of 300 pb^{-1}.Comment: 16 pages, 6 figure
The depletion in Bose Einstein condensates using Quantum Field Theory in curved space
Using methods developed in Quantum Field Theory in curved space we can
estimate the effects of the inhomogeneities and of a non vanishing velocity on
the depletion of a Bose Einstein condensate within the hydrodynamical
approximation.Comment: 4 pages, no figure. Discussion extended and references adde
Hawking radiation of massive modes and undulations
We compute the analogue Hawking radiation for modes which posses a small wave
vector perpendicular to the horizon. For low frequencies, the resulting mass
term induces a total reflection. This generates an extra mode mixing that
occurs in the supersonic region, which cancels out the infrared divergence of
the near horizon spectrum. As a result, the amplitude of the undulation
(0-frequency wave with macroscopic amplitude) emitted in white hole flows now
saturates at the linear level, unlike what was recently found in the massless
case. In addition, we point out that the mass introduces a new type of
undulation which is produced in black hole flows, and which is well described
in the hydrodynamical regime.Comment: 37 pages, 8 figures, published versio
Heavy-light decay topologies as a new strategy to discover a heavy gluon
We study the collider phenomenology of the lightest Kaluza-Klein excitation
of the gluon, G*, in theories with a warped extra dimension. We do so by means
of a two-site effective lagrangian which includes only the lowest-lying spin-1
and spin-1/2 resonances. We point out the importance of the decays of G* to one
SM plus one heavy fermion, that were overlooked in the previous literature. It
turns out that, when kinematically allowed, such heavy-light decays are
powerful channels for discovering the G*. In particular, we present a
parton-level Montecarlo analysis of the final state Wtb that follows from the
decay of G* to one SM top or bottom quark plus its heavy partner. We find that
at \sqrt{s} = 7 TeV and with 10 fb^{-1} of integrated luminosity, the LHC can
discover a KK gluon with mass in the range M_{G*} = (1.8 - 2.2) TeV if its
coupling to a pair of light quarks is g_{G*qqbar} = (0.2-0.5) g_3. The same
process is also competitive for the discovery of the top and bottom partners as
well. We find, for example, that the LHC at \sqrt{s} = 7 TeV can discover a 1
TeV KK bottom quark with an integrated luminosity of (5.3 - 0.61) fb^{-1} for
g_{G*qqbar} = (0.2-0.5) g_3.Comment: 36 pages, 13 figures. v2: a few typos corrected, comments added,
version published in JHE
Numerical observation of Hawking radiation from acoustic black holes in atomic Bose-Einstein condensates
We report numerical evidence of Hawking emission of Bogoliubov phonons from a
sonic horizon in a flowing one-dimensional atomic Bose-Einstein condensate. The
presence of Hawking radiation is revealed from peculiar long-range patterns in
the density-density correlation function of the gas. Quantitative agreement
between our fully microscopic calculations and the prediction of analog models
is obtained in the hydrodynamic limit. New features are predicted and the
robustness of the Hawking signal against a finite temperature discussed.Comment: Version 2 with enlarged text and several new figure
Asymptotic Safety, Emergence and Minimal Length
There seems to be a common prejudice that asymptotic safety is either
incompatible with, or at best unrelated to, the other topics in the title. This
is not the case. In fact, we show that 1) the existence of a fixed point with
suitable properties is a promising way of deriving emergent properties of
gravity, and 2) there is a sense in which asymptotic safety implies a minimal
length. In so doing we also discuss possible signatures of asymptotic safety in
scattering experiments.Comment: LaTEX, 20 pages, 2 figures; v.2: minor changes, reflecting published
versio