11,344 research outputs found
The Static Quantum Multiverse
We consider the multiverse in the intrinsically quantum mechanical framework
recently proposed in Refs. [1,2]. By requiring that the principles of quantum
mechanics are universally valid and that physical predictions do not depend on
the reference frame one chooses to describe the multiverse, we find that the
multiverse state must be static---in particular, the multiverse does not have a
beginning or end. We argue that, despite its naive appearance, this does not
contradict observation, including the fact that we observe that time flows in a
definite direction. Selecting the multiverse state is ultimately boiled down to
finding normalizable solutions to certain zero-eigenvalue equations, analogous
to the case of the hydrogen atom. Unambiguous physical predictions would then
follow, according to the rules of quantum mechanics.Comment: 27 pages, 2 figures; a typo in the abstract correcte
Higgs Descendants
We define a Higgs descendant to be a particle beyond the standard
model whose mass arises predominantly from the vacuum expectation value of the
Higgs boson. Higgs descendants arise naturally from new physics whose intrinsic
mass scale is unrelated to the electroweak scale. The coupling of to the
Higgs boson is fixed by the mass and spin of , yielding a highly
predictive setup in which there may be substantial modifications to the
properties of the Higgs boson. For example, if the decay of the Higgs boson to
is kinematically allowed, then this branching ratio is largely
determined. Depending on the stability of , Higgs decays may result in a
variety of possible visible or invisible final states. Alternatively, loops of
may affect Higgs boson production or its decays to standard model
particles. If is stable dark matter, then the mandatory coupling between
and the Higgs boson gives a lower bound on the direct detection cross
section as a function of the mass. We also present a number of explicit
models which are examples of Higgs descendants. Finally, we comment on Higgs
descendants in the context of the excesses near 125 GeV recently observed at
ATLAS and CMS.Comment: 9 pages, 7 figures; version to appear in Phys. Rev. D; v3 typos
correcte
Shape evolution and the role of intruder configurations in Hg isotopes within the interacting boson model based on a Gogny energy density functional
The interacting boson model with configuration mixing, with parameters
derived from the self-consistent mean-field calculation employing the
microscopic Gogny energy density functional, is applied to the systematic
analysis of the low-lying structure in Hg isotopes. Excitation energies,
electromagnetic transition rates, deformation properties, and ground-state
properties of the Hg nuclei are obtained by mapping the microscopic
deformation energy surface onto the equivalent IBM Hamiltonian in the boson
condensate. These results point to the overall systematic trend of the
transition from the near spherical vibrational state in lower-mass Hg nuclei
close to Hg, onset of intruder prolate configuration as well as the
manifest prolate-oblate shape coexistence around the mid-shell nucleus
Hg, weakly oblate deformed structure beyond Hg up to the
spherical vibrational structure toward the near semi-magic nucleus Hg,
as observed experimentally. The quality of the present method in the
description of the complex shape dynamics in Hg isotopes is examined.Comment: 19 pages, 14 figures, revised version including new results and
discussions, title changed, accepted for publication in Phys. Rev.
Spectroscopy of quadrupole and octupole states in rare-earth nuclei from a Gogny force
Collective quadrupole and octupole states are described in a series of Sm and
Gd isotopes within the framework of the interacting boson model (IBM), whose
Hamiltonian parameters are deduced from mean field calculations with the Gogny
energy density functional. The link between both frameworks is the
() potential energy surface computed within the
Hartree-Fock-Bogoliubov framework in the case of the Gogny force. The
diagonalization of the IBM Hamiltonian provides excitation energies and
transition strengths of an assorted set of states including both positive and
negative parity states. The resultant spectroscopic properties are compared
with the available experimental data and also with the results of the
configuration mixing calculations with the Gogny force within the generator
coordinate method (GCM). The structure of excited states and its
connection with double octupole phonons is also addressed. The model is shown
to describe the empirical trend of the low-energy quadrupole and octupole
collective structure fairly well, and turns out to be consistent with GCM
results obtained with the Gogny force.Comment: 17 pages, 12 figures, 4 table
Structural evolution in germanium and selenium nuclei within the mapped interacting boson model based on the Gogny energy density functional
The shape transitions and shape coexistence in the Ge and Se isotopes are
studied within the interacting boson model (IBM) with the microscopic input
from the self-consistent mean-field calculation based on the Gogny-D1M energy
density functional. The mean-field energy surface as a function of the
quadrupole shape variables and , obtained from the constrained
Hartree-Fock-Bogoliubov method, is mapped onto the expectation value of the IBM
Hamiltonian with configuration mixing in the boson condensate state. The
resultant Hamiltonian is used to compute excitation energies and
electromagnetic properties of the selected nuclei Ge and
Se. Our calculation suggests that many nuclei exhibit
softness. Coexistence between prolate and oblate, as well as between spherical
and -soft, shapes is also observed. The method provides a reasonable
description of the observed systematics of the excitation energy of the
low-lying energy levels and transition strengths for nuclei below the neutron
shell closure , and provides predictions on the spectroscopy of
neutron-rich Ge and Se isotopes with , where data are scarce
or not available.Comment: 16 pages, 20 figure
Supersymmetry, Naturalness, and Signatures at the LHC
Weak scale supersymmetry is often said to be fine-tuned, especially if the
matter content is minimal. This is not true if there is a large A term for the
top squarks. We present a systematic study on fine-tuning in minimal
supersymmetric theories and identify low energy spectra that do not lead to
severe fine-tuning. Characteristic features of these spectra are: a large A
term for the top squarks, small top squark masses, moderately large tan\beta,
and a small \mu parameter. There are classes of theories leading to these
features, which are discussed. In one class, which allows a complete
elimination of fine-tuning, the Higgsinos are the lightest among all the
superpartners of the standard model particles, leading to three nearly
degenerate neutralino/chargino states. This gives interesting signals at the
LHC -- the dilepton invariant mass distribution has a very small endpoint and
shows a particular shape determined by the Higgsino nature of the two lightest
neutralinos. We demonstrate that these signals are indeed useful in realistic
analyses by performing Monte Carlo simulations, including detector simulations
and background estimations. We also present a method that allows the
determination of all the relevant superparticle masses without using input from
particular models, despite the limited kinematical information due to short
cascades. This allows us to test various possible models, which is demonstrated
in the case of a model with mixed moduli-anomaly mediation. We also give a
simple derivation of special renormalization group properties associated with
moduli mediated supersymmetry breaking, which are relevant in a model without
fine-tuning.Comment: 56 pages, 24 figure
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