arXiv subjects

Jorge F. Soriano

Publications and source records attributed to Jorge F. Soriano.

32 records · Page 2Linked to original sources

arXiv2020

$H_0$ tension and the String Swampland

[Abridged] We realize the Agrawal-Obied-Vafa (AOV) swampland proposal of fading dark matter by the model of Salam-Sezgin and its string realization of Cvetic-Gibbons-Pope. The model describes a compactification of 6-dimensional supergravity with a monopole background on a 2-sphere. In 4 dimensions, there are 2 scalar fields, $X$ and $Y $, and the effective potential in the Einstein frame is an exponential with respect to $Y$ times a quadratic polynomial in the field $e^{-X}$. When making the volume of the 2-sphere large, namely for large values of $Y$, there appears a tower of states, which according to the infinite distance swampland conjecture becomes exponentially massless. If the standard model fields are confined on Neveu-Schwarz 5-branes the 6-dimensional gauge couplings are independent of the string dilaton in the string frame, and upon compactification to 4 dimensions the 4-dimensional gauge couplings depend on $X$ (rather than the dilaton $Y$) which is fixed at the minimum of the potential. This avoids direct couplings of the dilaton to matter suppressing extra forces competing with gravity. We show that this set up has the salient features of the AOV models, and ergo can potentially ameliorate the tension between local distance ladder and cosmic microwave background estimates of the Hubble constant $H_0$. Although the AOV proposal does not fully resolve the tension in $H_0$ measurements, it provides a dynamical dark energy model of cosmology that satisfies the de Sitter swampland conjecture. We comment on a viable solution to overcome the tension between low- and high-redshift observations within the AOV background and discuss the implications for the swampland program.

hep-th↗

arXiv2020

Toward a robust inference method for the likelihood of low-luminosity gamma-ray bursts to be progenitors of ultrahigh-energy cosmic rays correlating with starburst galaxies

Very recently, the Pierre Auger Collaboration reported a $4.5σ$ correlation between the arrival directions of the highest energy cosmic rays and nearby starburst galaxies. The cosmic rays producing the anisotropy signal have been proposed to originate in low-luminosity gamma-ray bursts (llGRBs). On the basis of the well-justified assumption that at redshift $z<0.3$ the host metallicity is a good indicator of the llGRB production rate, we show that the association of llGRBs and the starbursts correlating with Auger data is excluded at the 90% confidence level.

astro-ph.HE↗

arXiv2019

Isotropic charged cosmologies in infrared-modified electrodynamics

It has long been known that the covariant formulation of quantum electrodynamics conflicts with the local description of states in the charged sector. Some of the solutions to this problem amount to modifications of the subsidiary conditions below some arbitrarily low photon frequency. Such infrared modified theories have been shown to be equivalent to standard Maxwell electrodynamics with an additional classical electromagnetic current induced by the quantum charges. The induced current only has support for very small frequencies and cancels the effects of the physical charges on large scales. In this work we explore the possibility that this de-electrification effect could allow for the existence of isotropic charged cosmologies, thus evading the stringent limits on the electric charge asymmetry of the universe. We consider a simple model of infrared-modified scalar electrodynamics in the cosmological context and find that the charged sector generates a new contribution to the energy-momentum tensor whose dominant contribution at late times is a cosmological constant-like term. If the charge asymmetry was generated during inflation, the limits on the asymmetry parameter in order not to produce a too-large cosmological constant are very stringent $η_Q <10^{-131}- 10^{-144}$ for a number of e-folds $N=50-60$ in typical models. However if the charge imbalance is produced after inflation, the limits are relaxed in such a way that $η_Q<10^{-43}(100 \,\mbox{GeV}/T_Q)$, with $T_Q$ the temperature at which the asymmetry was generated. If the charge asymmetry has ever existed and the associated electromagnetic fields vanish in the asymptotic future, the limit can be further reduced to $η_Q<10^{-28}$.

hep-ph↗

arXiv2019

Performance and science reach of POEMMA for ultrahigh-energy particles

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is a potential NASA Astrophysics Probe-class mission designed to observe ultra-high energy cosmic rays (UHECRs) and cosmic neutrinos from space. POEMMA will monitor colossal volumes of the Earth's atmosphere to detect extensive air showers (EASs) produced by extremely energetic cosmic messengers: UHECRs above 20 EeV over the full sky and cosmic neutrinos above 20 PeV. We focus most of this study on the impact of POEMMA for UHECR science by simulating the detector response and mission performance for EAS from UHECRs. We show that POEMMA will provide a significant increase in the statistics of observed UHECRs at the highest energies over the entire sky. POEMMA will be the first UHECR fluorescence detector deployed in space that will provide high-quality stereoscopic observations of the longitudinal development of air showers. Therefore, it will be able to provide event-by-event estimates of the calorimetric energy and nuclear mass of UHECRs. The particle physics in the interactions limits the interpretation of the shower maximum on an event by event basis. In contrast, the calorimetric energy measurement is significantly less sensitive to the different possible final states in the early interactions. We study the prospects to discover the origin and nature of UHECRs using expectations for measurements of the energy spectrum, the distribution of arrival direction, and the atmospheric column depth at which the EAS longitudinal development reaches maximum. We also explore supplementary science capabilities of POEMMA through its sensitivity to particle interactions at extreme energies and its ability to detect ultra-high energy neutrinos and photons produced by top-down models including cosmic strings and super-heavy dark matter particle decay in the halo of the Milky Way.

astro-ph.HE↗

arXiv2019

Probing strong dynamics with cosmic neutrinos

IceCube has observed 80 astrophysical neutrino candidates in the energy range 0.02 < E_ν/PeV < 2. Deep inelastic scattering of these neutrinos with nucleons on Antarctic ice sheet probe center-of-mass energies $\sqrt{s} \sim$ 1 TeV. By comparing the rates for two classes of observable events, any departure from the benchmark (perturbative QCD) neutrino-nucleon cross section can be constrained. Using the projected sensitivity of South Pole next generation neutrino telescope we show that this facility will provide a unique probe of strong interaction dynamics. In particular, we demonstrate that the high-energy high-statistics data sample to be recorded by IceCube-Gen2 in the very near future will deliver a direct measurement of the neutrino-nucleon cross section at $\sqrt{s} \sim 1$ TeV, with a precision comparable to perturbative QCD informed by HERA data. We also use IceCube data to extract the neutrino-nucleon cross section at $\sqrt{s} \sim 1$ TeV through a likelihood analysis, considering (for the first time) both the charged-current and neutral-current contributions as free parameters of the likelihood function.

hep-ph↗

arXiv2019

Evidence for UHECR origin in starburst galaxies

The quest for the origin(s) of ultra-high-energy cosmic rays (UHECRs) continues to be a far-reaching pillar of high energy astrophysics. The source scrutiny is mostly based on three observables: the energy spectrum, the nuclear composition, and the distribution of arrival directions. We show that each of these three observables can be well reproduced with UHECRs originating in starburst galaxies.

astro-ph.HE↗

arXiv2019

Is there anybody out there?

The Fermi paradox is the discrepancy between the strong likelihood of alien intelligent life emerging (under a wide variety of assumptions) and the absence of any visible evidence for such emergence. We use this intriguing unlikeness to derive an upper limit on the fraction of living intelligent species that develop communication technology <ξ_{biotec}>. <...> indicates average over all the multiple manners civilizations can arise, grow, and develop such technology, starting at any time since the formation of our Galaxy in any location inside it. Following Drake, we factorize <ξ_{biotec}> as the product of the fractions in which: (i) life arises, (ii) intelligence develops, and (iii) communication technology is developed. In this approximation, the number of communicating intelligent civilizations that exist in the Galaxy at any given time is found to be N = <ζ_{astro}> <ξ_{biotec}> L_τ, where <ζ_{astro}> is the average production rate of potentially habitable rocky planets with a long-lasting (~ 4 Gyr) ecoshell and L_τ is the length of time that a typical civilization communicates. We estimate the production rate of exoplanets in the habitable zone and using recent determinations of the rate of gamma-ray bursts (GRBs) and their luminosity function, we calculate the probability that a life-threatening (lethal) GRB could make a planet inhospitable to life, yielding <ζ_{astro}> ~ 2 \times 10^{-3} yr^-1. Our current measurement of N =0 then implies <ζ_{biotec}> < 5 \times 10^{-3} at the 95\% C.L., where we have taken L_τ> 0.3 Myr such that c L_τ>> propagation distances of Galactic scales (~ 10 kpc), ensuring that any advanced civilization living in the Milky Way would be able to communicate with us.

astro-ph.HE↗

arXiv2019

The Galactic magnetic field in the light of starburst-generated ultrahigh-energy cosmic rays

Auger data show evidence for a correlation between ultrahigh-energy cosmic rays (UHECRs) and nearby starburst galaxies. This intriguing correlation is consistent with data collected by the Telescope Array, which have revealed a much more pronounced directional ``hot spot'' in arrival directions not far from the starburst galaxy M82. In this work, we assume starbursts are sources of UHECRs and investigate the prospects to use the observed distribution of UHECR arrival directions to constrain Galactic magnetic field models. We show that if the Telescope Array hot spot indeed originates from M82, UHECR data would place a strong constraint on the coherent and turbulent components of the Galactic magnetic field.

astro-ph.HE↗

arXiv2019

Hunting for super-heavy dark matter with the highest-energy cosmic rays

In 15 years of data taking the Pierre Auger Observatory has observed no events beyond $10^{11.3}$ GeV. This null result translates into an upper bound on the flux of ultrahigh-energy cosmic rays implying $J (> 10^{11.3}$ GeV) $< 3.6 \times 10^{-5}$ km$^{-2}$ sr$^{-1}$ yr$^{-1}$, at the 90\%C.L. We interpret this bound as a constraint on extreme-energy photons originating in the decay super-heavy dark matter (SHDM) particles clustered in the Galactic halo. Armed with this constraint we derive the strongest lower limit on the lifetime of hadronically decaying SHDM particles with masses in the range, $10^{14} < M_X/ $ GeV $< 10^{15}$. We also explore the capability of future NASA's POEMMA mission to search for SHDM signals.

hep-ph↗

arXiv2018

Ultrahigh-Energy Cosmic Ray Composition from the Distribution of Arrival Directions

The sources of ultrahigh-energy cosmic rays (UHECRs) have been difficult to catch. It was recently pointed out that while sources of UHECR protons exhibit anisotropy patterns that become denser and compressed with rising energy, nucleus-emitting-sources give rise to a cepa stratis (onion-like) structure with layers that become more distant from the source position with rising energy. The peculiar shape of the hot spots from nucleus-accelerators is steered by the competition between energy loss during propagation and deflection on the Galactic magnetic field (GMF). Here, we run a full-blown simulation study to accurately characterize the deflections of UHECR nuclei in the GMF. We show that while the cepa stratis structure provides a global description of anisotropy patterns produced by UHECR nuclei en route to Earth, the hot spots are elongated depending on their location in the sky due to the regular structure of the GMF. We demonstrate that with a high-statistics sample at the high-energy-end of the spectrum, like the one to be collected by NASA's POEMMA mission, the energy dependence of the hot-spot contours could become a useful observable to identify the nuclear composition of UHECRs. This new method to determine the nature of the particle species is complementary to those using observables of extensive air showers, and therefore is unaffected by the large systematic uncertainties of hadronic interaction models.

astro-ph.HE↗

arXiv2018

Probing QCD approach to thermal equilibrium with ultrahigh energy cosmic rays

The Pierre Auger Collaboration has reported an excess in the number of muons of a few tens of percent over expectations computed using extrapolation of hadronic interaction models tuned to accommodate LHC data. Very recently, we proposed an explanation for the muon excess assuming the formation of a deconfined quark matter (fireball) state in central collisions of ultrarelativistic cosmic rays with air nuclei. At the first stage of its evolution the fireball contains gluons as well as $u$ and $d$ quarks. The very high baryochemical potential inhibits gluons from fragmenting into $u \bar u$ and $d \bar d$, and so they fragment predominantly into $s \bar s$ pairs. In the hadronization which follows this leads to the strong suppression of pions and hence photons, but allows heavy hadrons to be emitted carrying away strangeness. In this manner, the extreme imbalance of hadron to photon content provides a way to enhance the muon content of the air shower. In this communication we study theoretical systematics from hadronic interaction models used to describe the cascades of secondary particles produced in the fireball explosion. We study the predictions of one of the leading LHC-tuned models QGSJET II-04 considered in the Auger analysis.

hep-ph↗

arXiv2018

The photo-disintegration of $^4$He on the cosmic microwave background is less severe than earlier thought

We thoroughly study the photo-disintegration of $^4$He on the cosmic microwave background using the most recent cross-section data both from the inclusive measurement observing the analog of the giant dipole resonance in $^4$He through the charge-exchange spin-flip $^4$He ($^7$Li,$^7$Be) reaction and from measurements of exclusive two-body and three-body processes: $^4{\rm He} \, (γ,p)\, ^3{\rm H}$, $^4{\rm He} \, (γ,n) \, ^3{\rm He}$, and $^4$He $(γ, pn)$ $^2$H. We show that the present-day (redshift $z=0$) mean free path of ultra-relativistic (Lorentz factor $\sim 10^{10}$) helium nuclei increases by more that $15\%$ with respect to previous estimates adopted as benchmarks for Monte Carlo simulation codes of ultrahigh-energy cosmic ray propagation. This implies that the physical survival probability of $^4$He nuclei would be larger than predicted by existing event generators. For example, for $E \sim 10^{10.8}~{\rm GeV}$ and a propagation distance of 3.5 Mpc, the $^4$He intensity would be $35\%$ larger than the output of CRPropa 3 program and $42\%$ larger than the output of SimProp v2r4 program. We provide new parametrizations for the two-body and three-body photo-disintegration cross-sections of $^4$He, $^3$He, tritium, and deuterium.

astro-ph.HE↗

arXiv2018

New test of Lorentz symmetry using ultrahigh-energy cosmic rays

We propose an innovative test of Lorentz symmetry by observing pairs of simultaneous parallel extensive air showers produced by the fragments of ultrahigh-energy cosmic ray nuclei which disintegrated in collisions with solar photons. We show that the search for a cross-correlation of showers in arrival time and direction becomes background free for an angular scale < 3^\circ and a time window {\cal O}(10 s). We also show that if the solar photo-disintegration probability of helium is {\cal O} (10^{-5.5}) then the hunt for spatiotemporal coincident showers could be within range of existing cosmic ray facilities, such as the Pierre Auger Observatory. We demonstrate that the actual observation of a few events can be used to constrain Lorentz violating dispersion relations of the nucleon.

hep-ph↗

arXiv2017

Evidence for a break in the spectrum of astrophysical neutrinos

The announcement by the IceCube Collaboration of the observation of 53 astrophysical neutrino candidates in the energy range 0.03 \alt E_ν/PeV \alt 2 has been greeted with a great deal of justified excitement. Herein we provide fits of single and a broken power-law energy-spectra to these high-energy starting events (HESEs). By comparing our statistical results from fits to (background-free) shower HESE data with the spectral shape of muon neutrinos recently reported by the IceCube Collaboration, we show that there is (3 σ) evidence for a break in the spectrum of astrophysical neutrinos. After that we use the fitted result to predict the rate of Glashow events (in the ~ 6.3 PeV region) and double-bang tau neutrino events (in the PeV region) just at the threshold of IceCube detection.

astro-ph.HE↗