327 research outputs found

### Causal Fermion Systems: An Elementary Introduction to Physical Ideas and Mathematical Concepts

We give an elementary introduction to the theory of causal fermion systems,
with a focus on the underlying physical ideas and the conceptual and
mathematical foundations.Comment: 24 pages, LaTeX, 3 figures, minor changes (published version

Recommended from our members

### Asymptotic sum rules

New sum rules from current algebra valid in the limit of large negative four-momentum squared of the current are obtained; some of these depend upon commutators of space components of the current densities. They contain convergence factors which make their validity plausible on most models of high-energy behavior, with the Regge-pole model being one of them. With one exception, their utility consists of placing constraints upon models of hadrons designed to saturate the current-algebra scheme. Â© 1968 The American Physical Society

### Semileptonic Hyperon Decays

We review the status of hyperon semileptonic decays. The central issue is the
$V_{us}$ element of the CKM matrix, where we obtain $V_{us}=0.2250 (27)$. This
value is of similar precision, but higher, than the one derived from $K_{l3}$,
and in better agreement with the unitarity requirement,
$|V_{ud}|^2+|V_{us}|^2+|V_{ub}|^2=1$. We find that the Cabibbo model gives an
excellent fit of the existing form factor data on baryon beta decays ($\chi^{2}
= 2.96$ for 3 degrees of freedom) with $F + D = 1.2670 \pm 0.0030$, $F - D =
-0.341 \pm 0.016$, and no indication of flavour-SU(3)-breaking effects. We
indicate the need of more experimental and theoretical work, both on hyperon
beta decays and on $K_{l3}$ decays.Comment: 37 pages, 8 figures, 4 tables, Final version of this material is
scheduled to appear in the Annual Review of Nuclear and Particle Science Vol.
5

### Aspects Of Heavy Quark Theory

Recent achievements in the heavy quark theory are critically reviewed. The
emphasis is put on those aspects which either did not attract enough attention
or cause heated debates in the current literature. Among other topics we
discuss (i) basic parameters of the heavy quark theory; (ii) a class of exact
QCD inequalities; (iii) new heavy quark sum rules; (iv) virial theorem; (v)
applications (|V_cb| from the total semileptonic width and from the B->D*
transition at zero recoil). In some instances new derivations of the previously
known results are given, or new aspects addressed. In particular, we dwell on
the exact QCD inequalities. Furthermore, a toy model is considered that may
shed light on the controversy regarding the value of the kinetic energy of
heavy quarks obtained by different methods.Comment: 67 pages, 6 Figures; plain LaTeX. Changes: Some equations in Sect.4
related to spin-nonsinglet sum rules are corrected. The references are
updated

### Energy Level Diagrams for Black Hole Orbits

A spinning black hole with a much smaller black hole companion forms a
fundamental gravitational system, like a colossal classical analog to an atom.
In an appealing if imperfect analogy to atomic physics, this gravitational atom
can be understood through a discrete spectrum of periodic orbits. Exploiting a
correspondence between the set of periodic orbits and the set of rational
numbers, we are able to construct periodic tables of orbits and energy level
diagrams of the accessible states around black holes. We also present a closed
form expression for the rational q, thereby quantifying zoom-whirl behavior in
terms of spin, energy, and angular momentum. The black hole atom is not just a
theoretical construct, but corresponds to extant astrophysical systems
detectable by future gravitational wave observatories.Comment: 8 page

### Do Proton-Proton collisions at the LHC energies produce Droplets of Quark-Gluon Plasma?

The proton-proton ($pp$) collisions at the Large Hadron Collider (LHC), CERN,
Switzerland has brought up new challenges and opportunities in understanding
the experimental findings in contrast to the conventional lower energy $pp$
collisions. Usually $pp$ collisions are used as the baseline measurement at the
GeV and TeV energies in order to understand a possible high density QCD medium
formation in heavy-ion collisions. However, the TeV $pp$ collisions have
created a new domain of research, where scientists have started observing
heavy-ion-like features (signatures) in high-multiplicity $pp$ collisions. This
warrants a relook into TeV $pp$ collisions, if at all QGP-droplets are produced
in such collisions. In this presentation, I discuss some of the new findings
and concepts emerging out in $pp$ collisions at the LHC energies along with
some of the new emergent phenomena in particle production.Comment: 5 pages, 4-captioned figures, Presented in the plenary session of
Workshop on Frontiers in High Energy Physics (FHEP-2019), Hyderabad, India
(To appear in Springer Proc.

### The temperature and entropy of CFT on time-dependent backgrounds

We express the AdS-Schwarzschild black-hole configuration in coordinates such
that the boundary metric is of the FLRW type. We review how this construction
can be used in order to calculate the stress-energy tensor of the dual CFT on
the FLRW background. We deduce the temperature and entropy of the CFT, which
are related to the temperature and entropy of the black hole. We find that the
entropy is proportional to the area of an apparent horizon, different from the
black-hole event horizon. For a dS boundary we reproduce correctly the
intrinsic temperature of dS space.Comment: 19 pages, major revision, several comments added, version to appear
in JHE

### Dark Force Detection in Low Energy e-p Collisions

We study the prospects for detecting a light boson X with mass m_X < 100 MeV
at a low energy electron-proton collider. We focus on the case where X
dominantly decays to e+ e- as motivated by recent "dark force" models. In order
to evade direct and indirect constraints, X must have small couplings to the
standard model (alpha_X 10 MeV).
By comparing the signal and background cross sections for the e- p e+ e- final
state, we conclude that dark force detection requires an integrated luminosity
of around 1 inverse attobarn, achievable with a forthcoming JLab proposal.Comment: 38 pages, 19 figures; v2, references adde

### Vectorlike Confinement at the LHC

We argue for the plausibility of a broad class of vectorlike confining gauge
theories at the TeV scale which interact with the Standard Model predominantly
via gauge interactions. These theories have a rich phenomenology at the LHC if
confinement occurs at the TeV scale, while ensuring negligible impact on
precision electroweak and flavor observables. Spin-1 bound states can be
resonantly produced via their mixing with Standard Model gauge bosons. The
resonances promptly decay to pseudo-Goldstone bosons, some of which promptly
decay to a pair of Standard Model gauge bosons, while others are charged and
stable on collider time scales. The diverse set of final states with little
background include multiple photons and leptons, missing energy, massive stable
charged particles and the possibility of highly displaced vertices in dilepton,
leptoquark or diquark decays. Among others, a novel experimental signature of
resonance reconstruction out of massive stable charged particles is
highlighted. Some of the long-lived states also constitute Dark Matter
candidates.Comment: 33 pages, 6 figures. v4: expanded discussion of Z_2 symmetry for
stability, one reference adde

- â€¦