824 research outputs found
Planckian Interacting Massive Particles as Dark Matter
The Standard Model could be self-consistent up to the Planck scale according
to the present measurements of the Higgs mass and top quark Yukawa coupling. It
is therefore possible that new physics is only coupled to the Standard Model
through Planck suppressed higher dimensional operators. In this case the WIMP
miracle is a mirage, and instead minimality as dictated by Occam's razor would
indicate that dark matter is related to the Planck scale, where quantum gravity
is anyway expected to manifest itself. Assuming within this framework that dark
matter is a Planckian Interacting Massive Particle, we show that the most
natural mass larger than is already ruled out by the
absence of tensor modes in the CMB. This also indicates that we expect tensor
modes in the CMB to be observed soon for this type of minimal dark matter
model. Finally, we touch upon the KK graviton mode as a possible realization of
this scenario within UV complete models, as well as further potential
signatures and peculiar properties of this type of dark matter candidate. This
paradigm therefore leads to a subtle connection between quantum gravity, the
physics of primordial inflation, and the nature of dark matter.Comment: 6 pages, 1 figure, Version published in PR
Patient Observers and Non-perturbative Infrared Dynamics in Inflation
We have previously derived the effect of soft graviton modes on the quantum
state of de Sitter using spontaneously broken asymptotic symmetries. In the
present paper we reinterpret this effect in terms of particle production and
relate the quantum states with and without soft modes by means of Bogoliubov
transformations. This also enables us to address the much discussed issues
regarding the observability of infrared effects in de Sitter from a new
perspective. While it is commonly agreed that infrared effects are not visible
to a single sub-horizon observer at late times, we argue that the question is
less trivial for a {\it patient observer} who has lived long enough to have a
record of the state before the soft mode was created. Though classically there
is no obstruction to measuring this effect locally, we give several indications
that quantum mechanical uncertainties may censor the effect. We then apply our
methods to find a non-perturbative description of the quantum state pertaining
to the Page time of de Sitter, and derive with these new methods the
probability distribution for the local quantum states of de Sitter and
slow-roll inflation in the presence of long modes. Finally, we use this to
formulate a precise criterion for the existence of eternal inflation in general
classes of slow-roll inflation.Comment: 37 page
Radiative Corrections from Heavy Fast-Roll Fields during Inflation
We investigate radiative corrections to the inflaton potential from heavy
fields undergoing a fast-roll phase transition. We find that a logarithmic
one-loop correction to the inflaton potential involving this field can induce a
temporary running of the spectral index. The induced running can be a short
burst of strong running, which may be related to the observed anomalies on
large scales in the cosmic microwave spectrum, or extend over many e-folds,
sustaining an effectively constant running to be searched for in the future. We
implement this in a general class of models, where effects are mediated through
a heavy messenger field sitting in its minimum. Interestingly, within the
present framework it is a generic outcome that a large running implies a small
field model with a vanishing tensor-to-scalar ratio, circumventing the normal
expectation that small field models typically lead to an unobservable small
running of the spectral index. An observable level of tensor modes can also be
accommodated, but, surprisingly, this requires running to be induced by a
curvaton. If upcoming observations are consistent with a small tensor-to-scalar
ratio as predicted by small field models of inflation, then the present study
serves as an explicit example contrary to the general expectation that the
running will be unobservable.Comment: 35 pages, 4 figures, matches published versio
Theory and Phenomenology of Planckian Interacting Massive Particles as Dark Matter
Planckian Interacting Dark Matter (PIDM) is a minimal scenario of dark matter
assuming only gravitational interactions with the standard model and with only
one free parameter, the PIDM mass. PIDM can be successfully produced by
gravitational scattering in the thermal plasma of the Standard Model sector
after inflation in the PIDM mass range from TeV up to the GUT scale, if the
reheating temperature is sufficiently high. The minimal assumption of a GUT
scale PIDM mass can be tested in the future by measurements of the primordial
tensor-to-scalar ratio. While large primordial tensor modes would be in tension
with the QCD axion as dark matter in a large mass range, it would favour the
PIDM as a minimal alternative to WIMPs. Here we generalise the previously
studied scalar PIDM scenario to the case of fermion, vector and tensor PIDM
scenarios, and show that the phenomenology is nearly identical, independent of
the spin of the PIDM. We also consider the specific realisation of the PIDM as
the Kaluza Klein excitation of the graviton in orbifold compactifications of
string theory, as well as in models of monodromy inflation and in Higgs
inflation. Finally we discuss the possibility of indirect detection of PIDM
through non-perturbative decay.Comment: 41 pages, 9 figures, V2: typos correcte
Optimising peak energy reduction in networks of buildings
Buildings are amongst the world’s largest energy consumers and simultaneous peaks in demand from networks of buildings can decrease electricity system stability. Current mitigation measures either entail wasteful supply-side over-specification or complex centralised demand-side control. Hence, a simple schema is developed for decentralised, self-organising building-to-building load coordination that requires very little information exchange and no top-down management—analogous to other complex systems with short range interactions, such as coordination between flocks of birds or synchronisation in fireflies. Numerical and experimental results reveal that a high degree of peak flattening can be achieved using surprisingly small load-coordination networks. The optimum reductions achieved by the simple schema can outperform existing techniques, giving substantial peak-reductions as well as being remarkably robust to changes in other system parameters such as the interaction network topology. This not only demonstrates that significant reductions in network peaks are achievable using remarkably simple control systems but also reveals interesting theoretical results and new insights which will be of great interest to the complexity and network science communities.</p
Using a Laguerre-Gaussian beam to trap and cool the rotational motion of a mirror
We show theoretically that it is possible to trap and cool the rotational
motion of a macroscopic mirror made of a perfectly reflecting spiral phase
element using orbital angular momentum transfer from a Laguerre-Gaussian
optical field. This technique offers a promising route to the placement of the
rotor in its quantum mechanical ground state in the presence of thermal noise.
It also opens up the possibility of simultaneously cooling a vibrational mode
of the same mirror. Lastly, the proposed design may serve as a sensitive
torsional balance in the quantum regime.Comment: New cavity design, reworked title; to appear in Phys. Rev. Let
Fermionic Symmetries: Extension of the two to one Relationship Between the Spectra of Even-Even and Neighbouring Odd mass Nuclei
In the single j shell there is a two to one relationship between the spectra
of certain even-even and neighbouring odd mass nuclei e.g. the calculated
energy levels of J=0^+ states in ^{44}Ti are at twice the energies of
corresponding levels in ^{43}Ti(^{43}Sc) with J=j=7/2. Here an approximate
extension of the relationship is made by adopting a truncated seniority scheme
i.e. for ^{46}Ti and ^{45}Sc we get the relationship if we do not allow the
seniority v=4 states to mix with the v=0 and v=2 states. Better than that, we
get very close to the two to one relationship if seniority v=4 states are
admixed perturbatively. In addition, it is shown that the higher isospin states
do not contain seniority 4 admixtures.Comment: 11 pages, RevTex file and no figures, typos added, references changed
and changed content
Roles of proton-neutron interactions in alpha-like four-nucleon correlations
An extended pairing plus QQ force model, which has been shown to successfully
explain the nuclear binding energy and related quantities such as the symmetry
energy, is applied to study the alpha-like four-nucleon correlations in
1f_{7/2} shell nuclei.
The double difference of binding energies, which displays a characteristic
behavior at , is interpreted in terms of the alpha-like
correlations. Important roles of proton-neutron interactions forming the
alpha-like correlated structure are discussed.Comment: 10 pages, 2 figures, RevTex, submitted to Phys. Rev.
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