arXiv subjects
Publications and source records attributed to Luis A. Anchordoqui.
Lecture script of a one-semester course that aims to develop an understanding and appreciation of fundemental concepts in modern physics for students who are comfortable with calculus. This document contains the first six lessons that will walk you through the special theory of relativity.
There is a new urgency for wider segments of the non-expert population to join in shaping the future direction of our technological society. Certain decisions being made now in the development of energy resources will profoundly affect the lives of the next few generations. This course is oriented toward providing an educational base for participating in these decisions. At this level, there is no need for any mathematics beyond simple arithmetic, nor for any previous knowledge of physics or chemistry.
The sharp change in slope of the ultrahigh-energy cosmic ray spectrum around 10^{9.6} GeV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle which evolves to intermediate/heavy composition above, has proved exceedingly challenging to understand theoretically. Recently, we introduced a very general model in which, for a range of source conditions, photo-disintegration of ultrahigh-energy nuclei in the region surrounding the accelerator naturally accounts for the observed spectrum and composition of the entire extragalactic component, which dominates above about 10^{8.5} GeV. In this communication we review the generalities of the model and show that starburst galaxies provide a compelling source example.
EUSO-SPB2 is a second generation Extreme Universe Space Observatory (EUSO) on a Super-Pressure Balloon (SPB). This document describes the physics capabilities, the proposed technical design of the instruments, and the simulation and analysis software.
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.
We re-examine the possibility of ultrahigh energy cosmic rays being accelerated in nearby dormant quasars. We particularize our study to heavy nuclei to accommodate the spectrum and nuclear composition recently reported by the Pierre Auger Collaboration. Particle acceleration is driven by the Blandford-Znajek mechanism, which wires the dormant spinning black holes as Faraday unipolar dynamos. We demonstrate that energy losses are dominated by photonuclear interactions on the ambient photon fields. We argue that the local dark fossils of the past quasar activity can be classified on the basis of how source parameters (mass of the central engine and photon background surrounding the accelerator) impact the photonuclear interaction. In this classification it is possible to distinguish two unequivocal type of sources: those in which nuclei are completely photodisintegrated before escaping the acceleration region and those in which photopion production is the major energy damping mechanism. We further argue that the secondary nucleons from the photodisintegrated nuclei (which have a steep spectral index at injection) can populate the energy region below "the ankle" feature in the cosmic ray spectrum, whereas heavy and medium mass nuclei (with a harder spectral index) populate the energy region beyond "the ankle", all the way to the high energy end of the spectrum. In addition, we show that five potential quasar remnants from our cosmic backyard correlate with the hot-spot observed by the Telescope Array.
We investigate left-right symmetric extensions of the standard model based on open strings ending on D-branes, with gauge bosons due to strings attached to stacks of D-branes and chiral matter due to strings stretching between intersecting D-branes. The left-handed and right-handed fermions transform as doublets under Sp(1)_L and Sp(1)_R, and so their masses must be generated by the introduction of Higgs fields in a bi-fundamental (2,2) representation under the two Sp(1) gauge groups. For such D-brane configurations the left-right symmetry must be broken by Higgs fields in the doublet representation of Sp(1)_R and therefore Majorana mass terms are suppressed by some higher physics scale. The left-handed and right-handed neutrinos pair up to form Dirac fermions which control the decay widths of the right-handed W' boson to yield comparable branching fractions into dilepton and dijets channels. Using the most recent searches at LHC13 Run II with 2016 data we constrain the (g_R, m_{W'}) parameter space. Our analysis indicates that independent of the coupling strength g_R, gauge bosons with masses m_{W'} \agt 3.5~{\rm TeV} are not ruled out. As the LHC is just beginning to probe the TeV-scale, significant room for W' discovery remains.
Cosmological parameters deduced from the Planck measurements of anisotropies in the cosmic microwave background are at some tension with direct astronomical measurements of various parameters at low redshifts. Very recently, it has been conjectured that this discrepancy can be reconciled if a certain fraction of dark matter is unstable and decays between recombination and the present epoch. Herein we show that if the superheavy relics have a branching into neutrinos B (X \to ν\bar ν) \sim 3 \times 10^{-9}, then this scenario can also accommodate the recently discovered extraterrestrial flux of neutrinos, relaxing the tension between IceCube results and Fermi LAT data. The model is fully predictive and can be confronted with future IceCube data. We demonstrate that in 10 years of observation IceCube will be able to distinguish the mono-energetic signal from X decay at the 3σlevel. In a few years of data taking with the upgraded IceCube-Gen2 enough statistics will be gathered to elucidate the dark matter--neutrino connection at the 5σlevel.
We show that the subset of high energy neutrino events detected by IceCube which correlate with the Galactic center (within uncertainties of their reconstructed arrival directions) could originate in the collisions of protons accelerated by the Sagittarius (Sgr) A* disk dynamo. Under very reasonable assumptions on source parameters we demonstrate that the supermassive black hole at the center of the Galaxy could launch protons and nuclei with multi PeV energies. Acceleration of these particles in a period of seconds up to Lorentz factors of \sim 10^7 is possible by means of the Blandford-Znajek mechanism, which wires the spinning magnetosphere of Sgr A* as a Faraday unipolar inductor. During the acceleration process the \sim PeV progenitors of \sim 50 TeV neutrinos radiate curvature photons in the keV energy range. We show that IceCube neutrino astronomy with photon tagging on the Chandra X-ray Observatory could provide a valuable probe for the Blandford-Znajek acceleration mechanism. We also argue that EeV neutrinos, which may be produced in a similar fashion during the merging of binary black holes, could become the smoking gun for particle acceleration in a one-shot boost.
This is a written version of a series of lectures aimed at undergraduate students in astrophysics/particle theory/particle experiment. We summarize the important progress made in recent years towards understanding high energy astrophysical processes and we survey the state of the art regarding the concordance model of cosmology.
We present yet another composite model explaining the relatively broad peak in the diphoton invariant mass distribution around 750 GeV recently observed at the LHC experiments. We consider the excess originates in bound states of vector-like fermions Q transforming under the electroweak group (but not QCD) of the standard model and which are also charged under a new SU(N_{TC}) QCD-like confining force. Since the new uncolored fields transform as SU(2) doublets they can acquire a mass through Yukawa interactions with the electroweak Higgs doublet, as quarks and leptons. We parametrize the Q-onium bound state using the Coulomb approximation and give a numerical fit to the diphoton excess consistent with no strong coupling effects up to about 30 TeV, which is the energy scale for next generation colliders. The range of allowed hypercharge Y_Q is given by 2.26 \leq Y_Q \leq 2.53 for N_{\rm TC} =2 and 2.17 \leq Y_Q \leq 2.31 for N_{\rm TC} = 3. The smoking gun for the model would be the discovery of Q-onia decaying into Higgs and Z-boson.
Motivated by the recent update on LHC searches for narrow and broad resonances decaying into diphotons we reconsider the possibility that the observed peak in the invariant mass spectrum at M_{γγ} = 750 GeV originates from a closed string (possibly axionic) excitation φ(associated with low mass scale string theory) that has a coupling with gauge kinetic terms. We reevaluate the production of φby photon fusion to accommodate recent developments on additional contributions to relativistic light-light scattering. We also study the production of φvia gluon fusion. We show that for both a narrow and a broad resonance these two initial topologies can accommodate the excess of events, spanning a wide range of string mass scales 7 \alt M_s/TeV \alt 30 that are consistent with the experimental lower bound: M_s > 7 TeV, at 95% CL. We demonstrate that for the two production processes the LHC13 data is compatible with the lack of a diphoton excess in LHC8 data within \sim 1σ. We also show that if the resonance production is dominated by gluon fusion the null results on dijet searches at LHC8 further constrain the coupling strengths of φ, but without altering the range of possible string mass scales.
We show that low-mass-scale string compactifications, with a generic D-brane configuration that realizes the standard model by open strings, can explain the relatively broad peak in the diphoton invariant mass spectrum at 750 GeV recently reported by the ATLAS and CMS collaborations. Under reasonable assumptions, we demonstrate that the excess could originate from a closed string (possibly axionic) excitation φthat has a coupling with gauge kinetic terms. We estimate the φproduction rate from photon-photon fusion in elastic pp scattering, using the effective photon and narrow width approximations. For string scales above todays lower limit M_s \approx 7 TeV, we can accommodate the diphoton rate observed at Run II while maintaining consistency with Run I data.
Lecture script of a one-semester course that aims to develop an understanding and appreciation of fundemental concepts in modern physics for students who are comfortable with calculus. This document contains the last part of the course where we introduce the concept of the quantum unit to describe the dynamic properties of subatomic particles and the interactions of matter and radiation.
The sharp change in slope of the ultra-high energy cosmic ray (UHECR) spectrum around 10^{18.6} eV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle which evolves to intermediate composition above, has proved exceedingly challenging to understand theoretically. We show that for a range of source conditions, photo-disintegration of ultra-high energy nuclei in the region surrounding a UHECR accelerator naturally accounts for the observed spectrum and composition of the entire extragalactic component, which dominates above about 10^{17.5} eV. The mechanism has a clear signature in the spectrum and flavors of neutrinos.
The sharp change in slope of the ultrahigh energy cosmic ray (UHECR) spectrum around 10^18.6 eV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle and intermediate composition above, has proved exceedingly challenging to understand theoretically, without fine-tuning. We propose a mechanism whereby photo-disintegration of ultrahigh energy nuclei in the region surrounding a UHECR accelerator accounts for the observed spectrum and inferred composition at Earth. For suitable source conditions, the model reproduces the spectrum and the composition over the entire extragalactic cosmic ray energy range, i.e. above 10^17.5 eV. Predictions for the spectrum and flavors of neutrinos resulting from this process are also presented.
We study the vacuum stability of a minimal Higgs portal model in which the standard model (SM) particle spectrum is extended to include one complex scalar field and one Dirac fermion. These new fields are singlets under the SM gauge group and are charged under a global U(1) symmetry. Breaking of this U(1) symmetry results in a massless Goldstone boson, a massive CP-even scalar, and splits the Dirac fermion into two new mass-eigenstates, corresponding to Majorana fermions. The lightest Majorana fermion (w) is absolutely stable, providing a plausible dark matter (DM) candidate. We show that interactions between the Higgs sector and the lightest Majorana fermion which are strong enough to yield a thermal relic abundance consistent with observation can easily destabilize the electroweak vacuum or drive the theory into a non-perturbative regime at an energy scale well below the Planck mass. However, we also demonstrate that there is a region of the parameter space which develops a stable vacuum (up to the Planck scale), satisfies the relic abundance, and is in agreement with direct DM searches. Such an interesting region of the parameter space corresponds to DM masses 350 GeV \alt m_w \alt 1 TeV. The region of interest is within reach of second generation DM direct detection experiments.
Very recently, the ATLAS and CMS collaborations reported diboson and dijet excesses above standard model expectations in the invariant mass region of 1.8 -2.0 TeV. Interpreting the diboson excess of events in a model independent fashion suggests that the vector boson pair production searches are best described by WZ or ZZ topologies, because states decaying into W^+W^- pairs are strongly constrained by semileptonic searches. Under the assumption of a low string scale, we show that both the diboson and dijet excesses can be steered by an anomalous U(1) field with very small coupling to leptons. The Drell-Yan bounds are then readily avoided because of the leptophobic nature of the massive Z' gauge boson. The non-negligible decay into ZZ required to accommodate the data is a characteristic footprint of intersecting D-brane models, wherein the Landau-Yang theorem can be evaded by anomaly-induced operators involving a longitudinal Z. The model presented herein can be viewed purely field-theoretically, although it is particularly well motivated from string theory. Should the excesses become statistically significant at the LHC13, the associated Zγ topology would become a signature consistent only with a stringy origin.