Letters in High Energy Physics

SModelS Database Update v1.2.3

2020-09-06T21:09:45+00:00


We present an update of the SModelS database with simplified model results from 13 ATLAS and 10 CMS searches for supersymmetry at Run 2. This includes 5 ATLAS and 1 CMS analyses for full Run 2 luminosity, i.e., close to 140 fb\(^{-1}\) of data. In total, 76 official upper limit and efficiency map results have been added. Moreover, 21 efficiency map results have been produced by us using MadAnalysis5, to improve the coverage of gluino-squark production. The constraining power of the new database, v1.2.3, is compared to that of the previous release, v1.2.2. SModelS v1.2.3 is publicly available and can readily be employed for physics studies.

Can Self-Replicating Species Flourish in the Interior of a Star?

2020-08-30T02:31:24+00:00

The existing view of biological life is that it evolves under suitable conditions in the low-temperature world of atoms and molecules on the surface of a planet. It is believed that any plausible extraterrestrial form of life must resemble the life on Earth that is ruled by biochemistry of nucleic acids, proteins, and sugars. Going against this dogma, we argue that an advanced form of life based upon short-lived species can exist inside main-sequence stars like our Sun.

A Generally Covariant Theory of Quantized Real Klein-Gordon Field in de Sitter Spacetime

2020-08-22T02:15:58+00:00

We propose in this paper a quantization scheme for the real Klein-Gordon field in de Sitter spacetime.
Our scheme is generally covariant with the help of vierbein, which is necessary usually for the spinor
field in curved spacetime. We first present a Hamiltonian structure and then quantize the field following
the standard approach. For the free field, the time-dependent quantized Hamiltonian is diagonalized by
Bogliubov transformation, and the eigenstates at each instant are interpreted as the observed particle states

at that instant. The interpretation is supported by the known cosmological redshift formula and the on-
shell condition of 4-momentum for a free field. Though mathematics is carried out in terms of conformal

coordinates for the sake of convenience, the whole theory can be transformed into any other coordinates
based on general covariance. It is concluded that particle states, such as vacuum states in particular, are
time-dependent and vacuum states at one time evolve into nonvacuum states at later times. The formalism
of perturbation is provided with en extended Dirac picture.

Normalization of the Ground State of the Supersymmetric Harmonic Oscillator

2020-08-05T22:02:49+00:00

Supersymmetry plays a main role in all current thinking about superstring theory. Indeed, many remarkable properties of string theory have been explained using supersymmetry as a tool. So far, there has been
no unbroken supersymmetry observed in nature, and if nature is described by supersymmetry, it must be
broken. Supersymmetry may be broken spontaneously at any order of perturbation theory or dynamically
due to nonperturbative effects. To examine the methods of supersymmetry breaking, special attention is
given to discuss the normalization of the ground state of the supersymmetric harmonic oscillator. This
study explains that perturbation theory gives incorrect results for both the ground-state wave function
and the energy spectrum and it fails to give an explanation to the supersymmetry breaking.

Effects of an H-μ-τ coupling in quarkonium lepton flavor violation decays

2020-06-30T00:37:29+00:00

In this work we study the consistency of a possible non-vanishing coupling Hμτ smaller than 0.25% as pointed by the CMS collaborations [1], with measured lepton flavor violation processes involving quarkonium. We show that the most promising channel to confirm this excess is to look for the lepton flavor tau decay into a f₀ and μ where the experimental limit could strongly improved with the new B factories as Belle II.

Applying New Physics to the Problems of the \(\eta′\to\pi^0\gamma\gamma\) Decay

2020-06-13T12:59:01+00:00

Rare decays of light mesons may be a discovery window for a new weakly coupled forces hidden at a low-energy QCD scale. BES-III Collaboration reported an observation of the rare decay \(\eta' \to\pi^0\gamma\gamma\). The observed decay width disagrees with the preliminary theoretical estimates. We show that this tension may be attributed to New Physics, presumably Dark Photon. For completeness, we consider a possible influence of New Physics on a similar well-measured decay \(\eta \to\pi^0\gamma\gamma\) and a recently measured one, \(\eta' \to\eta\gamma\gamma\), showing that the impact of the hypothetical Dark Photon may be also present in these decays.

The Thermodynamics of Relativistic Multi-Fluid Systems

2020-06-13T13:01:16+00:00

This article extends the single-fluid relativistic irreversible thermodynamics theory of Müller, Israel and
Stewart (hereafter the MIS theory) to a multi-fluid system with inherent species interactions. This is illustrated
in a two-fluid toy-model where an effective complex 4-velocity plays the role of a primary dynamical
parameter. We find that an observer who resides in the real-part of this universe will notice that their
knowledge of the universe parametrized using real, rather than imaginary, quantities are insufficient to fully
determine properties such as the total energy density, pressure or entropy, In fact, such an observer will
deduce the existence of some negative energy that affects the expansion of their perceived real universe.

A Brief Introduction to the Weak Gravity Conjecture

2020-10-17T08:44:09+00:00


The Weak Gravity Conjecture proposes that a theory with a gauge field that is coupled to gravity must have charged matter on which gravity acts as the weakest force. It also proposes that there is an intrinsic cutoff on such an effective theory, which corresponds to a tower of charged states, that is set by the strength of the gauge coupling (in Planck units). This article is a brief introduction to the Weak Gravity Conjecture, covering aspects of the motivations for it as well as various extensions and refinements.

Moduli Stabilisation and the Holographic Swampland

2020-12-09T23:06:17+00:00

We investigate whether Swampland constraints on the low-energy dynamics of weakly coupled, moduli- stabilised string vacua in AdS can be related to inconsistencies of their putative holographic duals or, more generally, recast in terms of CFT data. We find that various swampland consistency constraints are equivalent to a negativity condition on the sign of certain mixed anomalous dimensions. This condition is similar to well-established CFT positivity bounds arising from causality and unitarity, but not known to hold in general. The studied scenarios include LVS, KKLT, and both perturbative and racetrack stabilisation. Interestingly, the LVS vacuum (with \(\Delta_\varphi = 8.038\)) also appears to live very close to a critical value (\(\Delta_\varphi = 8\)) where the anomalous dimensions change sign. We finally point out an intriguing connection to the Swampland Distance Conjecture, both in its original and refined versions.