Author: Juan Rojo

Some relatives of mine have always been obsessed with the details of my work schedule. They were not really interested in the actual content of my research, but kept asking every time we met at what time I was expected to start working in the mornings, when was I allowed to leave work in the afternoon, how many days of holiday did I have per year, and so on. They were not alone: many of my friends, while I was pursuing my PhD, were also puzzled about what exactly I was doing at the university and how I spent my time there during the day.

So what actually do researchers all day round? How do they distribute their time? What on Earth does actually doing science really mean? Actually, we are pretty busy people, trying carry out at more or less the same time an ever-growing number of activities. To begin with, a researcher, specially if she is embedded into a university, is expected not only to carry out research, write papers, and request and secure external funding, she also has to teach, organise courses, supervise bachelor, master, and PhD thesis students, recruit teaching assistants, contribute to management tasks at the department, faculty, and university level, participate in selection committees of all sorts (hiring, promotion, evaluation, accreditation, curriculum), and one could go on more and more. On top of all this, one needs to add academic travels, participating in workshops and conferences, attending seminars, colloquia, and all kinds of related events. Moreover, note that several of these tasks can be considered on their own full-time jobs. It is thus natural to ask how at all is it possible to juggle all these responsibilities in a minimally efficient way? It would seem almost a mathematical impossibility to fit all of them within a 40-hour week ….

These already tricky boundary conditions are rendered even more stressing by the intrinsic inefficiency of some of the core activities that constitute the everyday life of researchers. A prime example of this is applying for research funding. It is very difficult to be able to carry out your research program without first securing external financial support (and in some countries, like in The Netherlands, literally impossible since all grants are to some extent personal). In addition, one of the most important criteria for the stabilisation of tenure trackers and early career researchers is their demonstrated ability to attract external funding. All this would be very reasonable, if not for the fact that the plummeting success rates imply that most of the sizeable amount of effort that researchers invest in writing grant applications is demonstrably wasted time.

The same considerations apply to other facets of academia. For many of my colleagues, it is not the large workload that represents the most challenging aspect of their job, but rather it is the futility of many parts of it. In other words, it is not the hard work itself, but the pointlessness of some (or many) of our core activities, which is the source of endless frustration. Meetings, needless to say, fall also straight on in this category. It is not uncommon that I have back-to-back meetings the whole day, and I consider myself as someone with a relatively light teaching and management load. While some meetings are useful and productive, and thus necessary, some others are utterly irrelevant – nothing sinks your heart as having to sit through a 2-hour meeting with the certainty that this is time lost forever. Moreover, (many) academics are the kind of people that enjoy listening to themselves, so meetings often become a succession of incoherent interventions rather than a truly productive conversation.

Given the many pressures of academia, and the limited time available, it is not surprising that one often hears or reads the statement that science cannot be considered as a regular nine-to-five job, and that committed researchers, if they really want to strive for excellence and be successful in their careers, should be able to sustain a workload of say 70 or 80 hours per week during extended period of times. In addition, they should also be able to endure endless travels, attend conferences all over the world for networking and to publicise their results, and accept all possible requests of service and committee memberships that they receive, without forgetting various other important duties such as for example being editors and referees of journals and academic publications. Needless to say again, the same people expect that scientists should also of course check their emails at all times, and reply immediately even late at night or during weekends and holidays. Is it therefore true that only those scientists so devoted to their work that they would deserve the appropriate label of workaholics will attain success and reach the pinnacles of Academia?

On the one hand, It cannot be denied that being successful in academia in general, and in scientific research in particular, requires to work very hard, to be focused and well organised, and to some extent also to make sacrifices in your personal life. On the other hand, it is a demonstrably false statement that success can only be achieved by systematic working overtime evenings, weekends, and even holidays. Sure, there are times when an extra push is required, for example to meet a deadline, or to finalise a publication, but as a general rule keeping a healthy balance between your work and personal life will in the long term make you a more effective (and thus succesful) scientist, and, even more importantly, a happier person. Moreover, while everyone is free to manage their time as they find more appropriate, those PIs (principal investigators) that impose this workaholism viewpoint to the junior members of their groups and expect nothing else from them than complete devotion with immediate replies to their email requests even on weekends and holidays, in addition to violating labor law, are deliberately putting them in a dangerous situation and making them likely to experience burn-out or be affected by the mental health issues that ravage academia.

Though deriving conclusions based on a N=1 sample is not very scientific, I have been basically working “office hours” my whole scientific life and I think I can be reasonably happy with the end result. This means in particular I have never worked on weekends and very seldom on evenings, unless there are deadlines that, procrastinators as we are, we struggle to meet at the last minute. And I don’t think for a minute that I would have been more succesful, productive, and happier had I worked overtime systematically, most likely the opposite would be true (not that I had much choice with childcare duties since the end of my PhD!). This said, this does not mean that I switch off my brain to science while I am outside the office, since I fear that I am well past this point. For example, I start putting together grant proposals or papers when doing household chores: in particular I strongly recommend vacuuming for pumping your imagination in case you need a catchy title for your proposal, in my experience this has worked pretty well 😉

Ok, all this is very nice, but still one has to manage a rather heavy workload. So how does this work in practice? Again speaking from my experience, I would say that they key point is not working more, but in working better and being more efficient and selective. Scientific research is not quite the same as say building a pyramid, where if you spend twice the time you will (hopefully) get twice the job done. There are many cases in which working more leads to diminishing return, and there is plenty of scientific evidence that productivity drops after working a given amount of hours. You simply cannot be productive for 12 hours in a row, no matter how you put it, at least in a systematic way. So with the risk of sounding like a dubious self-help guru, here you have some tips that can help in this respect.

• Be very selective: attend only the really important seminars and conferences, and drop everything else. Try to ensure as much quality time as possible to write and carry out research, and if this involves not attending every single seminar or colloquia scheduled in your department, then so be it.
• Say no to things. You don’t need to accept every possible invitation to give a talk abroad, to write an invited chapter or to participate in the organisation of that conference. All these things are important but also time consuming, so prioritise what are the most relevant opportunities and politely decline everything else.
• Cluster you days in coherent groups of activities. For example, one can have days where all the meetings in the week are scheduled, including student supervision, or the days where one focuses only on writing papers or preparing lectures. You can have “teaching days”, “management days”, “research days”, and likewise, and in those days focus only on that activity and postpone everything else.
• Do not check email compulsively. Check email maybe every hour or two hours, and only answer the really urgent ones. You can then answer the less urgent emails at a later stage. A very succesful physicists whom I know very well never checks his email during the week and only checks it and replies on Fridays (of course this person has an administrative assistant so please do not take him as example, but you see my point).
• Choose carefully your research projects and collaborators. Toxic, inefficient, or absent collaborators can delay significantly the completion of a project and the production of scientific results, subtracting that much-needed time from other urgent tasks.
• Never be afraid of dumping projects if at some point you see that it is leading nowhere. Cut your losses and move on, never get stuck just trying to finish something for the sake of it.

Many more could be said, but you get the idea. Work hard, but also work smart. Be selective and focus on what is important. And never postpone “real life” because of science, since then it might be difficult (or even impossible) to recover the lost time.

When discussing about the various options concerning the future of particle physics, in particular in the context of the Update of the European Strategy for Particle Physics, the Higgs boson plays certainly a most important role. The Higgs is truly a unique beast, whose mysterious properties we have just started to unveil. Therefore, also motivated by some recent discussions on Twitter, I though it would be appropriate to write something about why moving forward with the ongoing charting of the Higgs boson sector should be the cornerstone for any future development in particle physics, and in particular why such study is immensely more important for our fundamental understanding of Nature, and represents a much higher goal than a mere bureaucratic rubber-stamping of the Standard Model.

Let me try to motivate why the Higgs boson is a particle like no one humankind has ever encountered before. To begin with, the Higgs boson is the first and only elementary scalar particle ever found. In quantum theory, all elementary particles carry a quantum number known as spin, which can be understood as some form of intrinsic angular momentum (picture a ball spinning around some axis, but now this ball is point-like, with a vanishing radius). Before the LHC discovery of the Higgs boson in 2012, we had found either spin-1/2 particles (such as the quarks and the electrons) or spin-1 particles (such as the photon), but never spin-0 particles. And the implications of this seemingly innocuous property are actually vast: while spin-1/2 and spin-1 particles have masses that are protected from large quantum corrections due to symmetry principles, spin-0 particles such as the Higgs boson do not, implying that in principle they can be sensitive to extremely high scales. This delicate sensitivity, called sometimes the hierarchy problem, is not a conceptual limitation of the theory, but it represents a rather dramatic breakdown of the extremely successful principle of separation of scales. This principle tells us, in a nutshell, that for example we don’t need to know about the existence of the strong force to describe the chemistry of molecules, since the two phenomena act at well-separated energies and distances. Unless there are new particles around, currently unknown, the Higgs boson mass actually depends on the physics that take place at very large energies, which is quite weird and unexpected.

Another facet of the unique character of the Higgs boson stems from the fact that it also drives the only fundamental interaction which is not determined by the gauge principle. Putting gravity aside (that can also be written in the form of a gauge theory), the three fundamental interactions (the electromagnetic, strong, and weak forces) follow the same basic principles, and their behaviour is fixed by tight symmetry principles. The Yukawa couplings between the Higgs boson and the quarks and charged leptons thus represents a rather startlingly different type of fundamental force, which deserves intense scrutiny. It is worth mentioning here that, while the ATLAS and CMS measurements have demonstrated that the Higgs boson is the responsible for the mass of the heavier fermions (the bottom and top quarks, and the tau lepton), we still have no evidence that this is also the case for the lighter muon and charm quark, let alone for the up and down quarks and the electron that constitute the nucleon and thus the overwhelming majority of all visible mass in the Universe! For all we know, the humble electron could receive its mass from a completely different mechanism that the one in the Standard Model. Thus trying to pin down the interplay between the Higgs mechanism and the masses of the lighter fermions is also a topic of utmost importance for our understanding of elementary particles and their interactions.

Indeed, as opposed to the gauge sector of the Standard Model, whose properties are exquisitely determined by elegant symmetry principles, the Higgs sector is truly a “model”, more than a theory. In its current formulation, it is a combination of ad hoc ingredients and minimality, not following any symmetry principle, and leads to a large number of free parameters to be extracted from the experimental data. It is simple and it seems to work, but we really don’t have an understanding of why this is the case in terms of deeper principles. So conceptually this situation is very unsatisfactory. We are thus still a long way to elucidate the mystery of electroweak symmetry breaking, in other words, the underlying reason of why elementary particles acquire any mass at all rather than being massless. This is why it has been argued that the Higgs sector of the Standard Model is likely to be an effective description of a more sophisticated theory at high energies, in the same way as how the Landau phenomenological model of superconductivity was eventually replaced by the more fundamental BCS theory.

Another of the major unknowns of the Higgs sector, and actually of the Standard Model itself, is given by the strength (or even the very existence) of the self-interactions of the Higgs boson. Given that the self-coupling of a fundamental scalar particle represents a truly new type of force, different from anything we’ve found before, the quest for the Higgs self-interactions is one the central goals of the LHC program. Moreover, a measurement of the Higgs self-coupling would provide crucial information on the electroweak symmetry breaking mechanism, probe the underlying strength of the Higgs interactions at high energies, such as testing the composite nature of the Higgs boson, and might be related to the matter-antimatter asymmetry of the Universe in the context of electroweak baryogenesis scenarios. A precise determination of the Higgs boson self-interaction would be, almost by itself, a strong enough justification for a future collider.

The Higgs self-coupling can be probed in two different ways, as shown schematically below. On the one hand, one can access via double Higgs production, where a pair of Higgs bosons is produced simultaneously. On the other hand, the Higgs self-coupling can also be accessed indirectly via virtual corrections to single Higgs production. In this latter case, one needs to measure very precisely differential distributions of single-Higgs production and compare them with theory calculations that include these higher order effects to constrain the Higgs self-interactions. These two pathways to probe the Higgs self-coupling are complementary: one is more direct but is less frequent, while the other is indirect but benefits from a higher abundance of events.

For all these various reasons, elucidating the properties of the Higgs boson offers an ideal probe to search for novel particles and interactions that might lie beyond the Standard Model. In addition, the Higgs could very well act as a portal to address some of the biggest mysteries in particle physics and cosmology such as the explanation of the tiny neutrino masses, the nature of dark matter, or the origin of the matter-antimatter asymmetry in the Universe. The Higgs is indeed a unique probe of the zeptouniverse, the microscope with the highest resolution conceivable so far. Thus the detailed understanding of its various properties should be one of the drivers for both short- and long-term efforts in high-energy physics.

It is also worth emphasising that we do not aim to measure more precisely the properties of the Higgs boson just for the sake of it, to know what number occupies the fifth decimal place in some coupling. The key observation in this respect is that in quantum field theory, the mathematical language that describes elementary particles, precision often gives you indirect access to energies and distances far beyond those that you can probe directly at particle colliders. This feature is nicely illustrated in this summary plot below, produced in the context of the ESPPU, that highlights how, when interpreted in the effective field theory context, the measurements of the Higgs boson properties and couplings at future colliders can provide access up to and above 50 TeV in specific scenarios (recall that the LHC center-of-mass energy is currently 13 TeV). In other words, the precision characterisation of the Higgs boson properties provides an extremely powerful microscope that allows us to study the fundamental laws of Nature at very small distances and extreme energies.

Of course you don’t need to only take my word for the crucial importance of the Higgs boson in modern particle physics: you can watch how a selected group of notorious particle physicists play and sing it! The video below is the of the theme songs of the biannual Physics at TeV Colliders workshop, which gathers LHC physicists in an iconic venue in Les Houches in the French Alps, to discuss recent progress in collider physics and work in collaborative projects. You can even find the whole lyrics here. It’s all about that Higgs, ’bout that Higgs, ….

Universities, the temples of higher education, are supposed to deliver excellent, flawless teaching. University professors should always be, at least according to PR leaflets and websites, inspiring, motivated teachers, and devoted mentors that guide their students through the fascinating adventure of learning. However, while there are of course a large number of outstanding university professors who truly drive their students’ learning, there are many others that struggle when put in front of a classroom. How can this be the case? Who teachers the teachers? This is a bit of a chicken-and-egg question, but it is worth asking ourselves what kind of extensive training and preparation do university professors undergo before they start teaching.

Upon a brief moment of reflection, it should be not too difficult to realise that there exist several reasons for why university professors are not necessarily that good at what should be one of the core duties of their job. First of all, few university staff are recruited solely on the basis of their pedagogical skills. In most cases, there are other factors that carry much more weight in the selection and hiring procedure, such as their research productivity and impact, and even more important lately, their demonstrated ability and potential to attract external funding (assuming that any such a thing is real). So, when looking for a job in academia, early career scholars and scientists have all incentives to boost their research portfolio, and little to devote their limited time to teaching, even less to investigate, pursue, and implement new educational approaches.

Moreover when hired, for instance at the Assistant Professor level, most scientists have had only a rather reduced exposure to teaching. Perhaps they have taken care of small-group tutorials, or have been in charge of supervisions, but few have experienced the burden of coordinating and teaching a large bachelor course with say more than one hundred students. Indeed, unbeknown to many people, teaching involves much (but really, like a lot) more than the mere time spent in the lecture room with the chalk in hand. It also requires setting up a bunch of detailed documents such as the syllabi and the study guides, determine and produce the evaluation and assessment methods, prepare material including lecture notes, handouts and slides, and all this checking that the various university regulations (and there are a lot of these) have been religiously obeyed. Then one has the marking, addressing the students’ questions and doubts, being available for office time and the like. In a nutshell, it is not a walk in the park, and in most cases the only way to prepare for the job by talking to your peers, trial and error, and of course by actually doing it.

A second reason why excellence in teaching is not as frequent in our universities as one might naively think has to do with the fact that, for all the many devoted and enthusiastic teachers around, there are also many professors who simply don’t care much about the students in front of them in the classroom. For many scientists, teaching is a disruption from their really important activities such as doing experiments, writing papers, and requesting (and securing) funding, while students represent a nuisance that should be avoided as much as possible. At most, they can be tolerated as an eventual source of personnel for their labs, but that is as far as it gets. The fact that many university departments reward their more successful staff with significant teaching reductions is a further sign highlighting the underlying priorities.

A third possible reason of why even highly successful researchers can become rather lousy teachers arises from the fact that, for an activity that is supposed to represent an integral part of our job, we receive surprisingly little training on how to become a good instructor. Mostly, we are supposed to learn the trade by imitation, and we tend to spend much less time thinking about what works and what not in education as compared to what we do in our research activities. Even between those of us that devote our efforts to the hard sciences there is often little interest to investigate what actually works and what not, at the quantitative level, from the pedagogical and educational perspective.

Such position can be inefficient or even dangerous for several reasons. First of all, it often assumes that all students are more or less like ourselves, and that we should teach them using the same methodology as that of our own favourite teachers. But this is far from being the case: the fact that I would definitely enjoy a heavy lecture with lengthy mathematical derivations does not necessarily mean that my students will also benefit, even less enjoy, from a similar type of lecture (and this is as it should be!). There exist many different types of learners, and focusing on a single type based on our own preferences is definitely a pedagogical bias that we should strive to avoid. Statistically speaking, our students are very different from ourselves, and this should be seen as an opportunity rather than as a drawback. Moreover, there exist a large degree of variation in interest, skills, and receptivity in our student population, and tailoring our teaching methods to a specific subset of this population (perhaps to the one that we consider to be composed by the ideal students) is not only rather pedagogically inefficient, it is also unfair with the rest of our students. As access to higher education widens up and our students become more and more diverse, we should be more careful in considering who do we have in front of us and what are the strategies that could work best to assist them in their learning, as opposed to those that we, subjectively, believe to be the best ones.

Ok, then you might ask, perhaps we should start teaching some teachers how to do their job better?  Well, the good news is that more often than not one does not need to implement burdensome measures or to motivate our staff to undergo extensive training: there are many simple, cost-effective measures that can lead to significant improvements in student learning. The first is perhaps really obvious, but one can never underestimate its vital importance: talking a lot. Talk to the students to check how the course is going, what works and what not, what are the points they find more challenging and where do they struggle. In my experience, student feedback represents a useful resource to improve the courses, and one should not wait until it is too late to gather it. Talk also to fellow teachers and instructors, gather statistics about their experiences, their ideas, what has been successful for them. Everyone enjoys doing their job better, and stubborn as academics can be, when presented with ideas that work they are the first to take them on board. And talk also with the management, with people that have a broad view of the local education ecosystem, with program and education directors. Be of course also critical with the input that you receive from them, but also be open to learn new things that eventually will make you a better teacher.

A second low-cost measure to improve students’ learning is to find the most efficient methods to communicate knowledge. For example, one of my little personal crusades is to reduce the use (and abuse) of slides and powerpoints in the classroom, especially for foundational courses. While using slides might be justified in some contexts, for example in large classrooms, I strongly believe that nothing beats a good old blackboard (whiteboards are also fine though!). Sure, you will cover less material, but this is fine: the main goal of a lecture is that the students learn something, as opposed to everything. Moreover, using blackboards naturally slows you down, so for students is easier to follow, take notes, and in general feel more engaged with the lecture. Well, many people often object, but I do have a horrible handwriting, or I don’t know how to draw graphs, or I am messy with the blackboard. Again, this is fine: just provide handouts or lecture notes, all the relevant information will still be available, and the most important process of all, which is the knowledge transfer between the teacher and the students, will have happened anyway. Someone once told me that in some countries the use of slides is banned for bachelor courses. While being perhaps too extreme (every course, instructor, and students are different so flexibility is important) I believe that such a measure goes into the right direction.

Of course, at the end of the day there is no substitute for passion. All pedagogical theories and technological support pale in front of a motivated, engaging teacher who loves to communicate knowledge and to educate students. But supplementing this passion with a few of mostly common-sense tips can go a very long way in significantly improving the teaching and learning experience in our universities, both for the instructors and for the students.

Since I am still exploring the potentialities of the blog, I will try next to summarise one of my recent research publications, which addresses the rather non-trivial point of whether or not possible new physics beyond the Standard Model can be confounded by effects of the strong interaction. Let’s see how this works out!

At hadron colliders such as the Large Hadron Collider (LHC), one accelerates protons up to almost the speed of light and then makes them collide. By reconstructing the debris of such very energetic collisions, we can have access to the laws of nature at the smallest of the distances, well below the atomic or the nuclear radius. Since protons are not fundamental particles, the LHC is more of a Large Quark and Gluon Collider (LQGC), though it is unlikely that this acronym will catch up. Therefore, to be able to make predictions about what will happen at the LHC, for example how many Higgs bosons will be produced within a year, it is not enough to know the energy of the colliding protons: we also need to determine how this energy is distributed among the proton’s constituents, namely the quarks and gluons.

The information about the energy distribution of the quark and gluons in the proton is encoded by quantities called the Parton Distribution Functions (PDFs), see here for a rather extensive recent review. We cannot compute these PDFs from first principles, at least with current technology, so we need to extract them from experimental data using a global QCD analysis – basically a big fitting machinery where the parameters that define the PDFs are adjusted to maximise the agreement with the input experimental data.

A recent development in this context has been the availability of LHC measurements themselves to constrain the PDFs. For example, one can use the production of top quark pairs to obtain information on the gluon content of the proton. As you can see from the Feynman diagram below, the production of top quark pairs provides direct information on the gluon content of the proton. The same holds for many other processes, for example, the production of a lepton-antilepton pair, the so call Drell-Yan process, allows us to separate the quark and antiquark content, and disentangle different quark flavours among them.

As the LHC accumulates more and more data, these PDF-sensitive measurements start to probe higher and higher scales, well above the Higgs boson mass. While in our determination of the PDFs we always assume that the Standard Model calculations are valid everywhere, if new physics Beyond the Standard Model are present within the LHC reach (perhaps in the form of subtle deviations with respect the SM predictions) there is the real risk that they would be “fitted away” into the PDFs. In other words, you would be missing out a unique opportunity to identify deviations with respect to the Standard Model since you have reabsorbed them into the PDFs!

One possible way to eliminate this risk is by determining simultaneously the PDFs together with this possible New Physics effects. So in our paper we performed the first join extraction of the PDF parameters and of the coefficients of the Standard Model Effective Field Theory (SMEFT). The SMEFT is a powerful theoretical framework that encodes in a model-independent way the effects of any new physics scenario at high energies that reduces to the SM at low energies. The question we want to address is to which extent these SMEFT effects can be reabsorbed into the PDFs. In other words, is new physics hiding in plain sight and we are just fooling ourselves since we are fitting it away into our QCD parameters?

One first check is to perform a sampling of the SMEFT parameter space and run PDF fits for a number of benchmark points. Does the fit quality improve once these additional New Physics parameters are added? The answer is that it does, though not dramatically. As you can see below, the fit quality (quantified by the ) improves at the post-fit level, that is, once the PDFs are readjusted to match the change in underlying theory as compared to the SM assumption. The effect is not dramatic but noticeable, showing that yes, indeed, partially new physics effects can be absorbed into the PDFs.

If this is the case, how we can tell SM effects from possible new physics ones? One can exploit kinematical differences between effects that arise from the strong interaction (one of the three fundamental forces that compose the Standard Model) and those related to physics beyond the SM. They key aspect here is the different dependence on the energy of these effects. In the case of the strong force, as we go towards higher energies we expect differences that scale as , while in the case of SMEFT corrections, they scale as . In the previous equations, is the typical mass scale of the strong interactions (basically one third of the proton mass) while is the (unknown) energy scale where new physics beyond the SM appear. And indeed, if one plots the fit quality as a function of the energy of the process, one observes a very different trend in the case of the Standard Model (feeble dependence with the energy) and in the SMEFT case (strong sensitivity to changes in the energy). Such trend would be the smoking gun to disentangle QCD and new physics effects within the global fit.

To summarise, in this work we have successfully demonstrated how one can disentangle possible BSM effects within the global PDF analysis. The next step will be to carry out a more extensive interpretation of LHC measurements as well as to explore a basis as wide as possible in the SMEFT parameter space.

Disclaimer: I write a first version of this article as part of my guest blogging in the Particle Physics People blog at Interactions.org. Given the intense discussions about the future of high energy physics that are taking place in the last months, including the update of the European Strategy, I though it would be nice to extend a bit this entry and post it this time in my new blog. Hopefully this will also allow testing the comments functionalities!

It is a well known fact within the community that high energy Physics finds itself at a crossroads. Paradoxically, the main reason for this state of affairs is none other than the extreme success of both our theoretical framework and our experimental programs. Indeed, our current understanding of elementary particles, as encapsulated by the Standard Model, has so far been confirmed with exquisite precision by countless experiments, except for a handful of anomalies that might or might not lead to something deeper. Even then, there are plenty enough urgent fundamental questions that are so far left unanswered! Indeed, while the discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations implies that there are no obvious targets of where the next layer of complexity in our understanding of physical reality can be identified, we should not be idle and keep pushing our efforts towards addressing these pressing questions.

To begin with, the Standard Model (SM) does not provide a candidate for dark matter, the mysterious non-luminous form of matter five times more abundant than normal matter and whose existence we infer from astronomical observations. It does not provide either a microscopic mechanism for the dark energy accelerating the expansion of the universe. Neither does the SM explain how the observed asymmetry between matter and antimatter was generated in the early universe, nor the fact that neutrinos have non-zero masses. While some of these puzzles have different levels of relevance (for example, it is not complicated to augment the Standard Model to include neutrino masses), all of them are truly fundamental questions which we should work hard to answer if our goal is to understand Nature at its deepest levels.

In addition to these ’observational’ conundrums, the SM also contains several puzzles of a more theoretical nature. To begin with, we still don’t know for sure if the scalar boson observed at the LHC is really the SM Higgs boson, or if it is instead a more complicated creature. For example, it could very well be that the Higgs is a composite particle itself, in the same way as how protons are not fundamental but rather composed by quarks and gluons. In addition, in the SM the mass of the Higgs boson is not protected by any symmetry, and for this reason it will tend to grow up to the highest energies at which the theory is valid. In this respect, we do not really understand the unbearable lightness of the Higgs particle. We also have no clue whatsoever of the origin of the flavour structure in the SM, for instance why there are three generations and not 27, and what mechanism determines the observed values of the masses of the SM particles. Moreover, the Higgs boson interactions are mediated by a force completely different from any of the forces we know (such as electromagnetism, drive by the gauge principle) so if there are any hidden sectors beyond the SM the Higgs offers a unique portal to access therm. So there is definitely no lack of fascinating problems to be tackled! Whether these theoretical puzzles are real conceptual issues or not is hotly debated within the community. For example, perhaps the flavour puzzle is merely a consequence of anthropic selection, as speculative as the latter is. In any case is clear that there is still a lot to learn about fundamental physics at the higher energies and smallest distances.

Going even deeper into the foundations of high-energy physics, we don’t know how to marry the two most arguably successful physical theories ever formulated, quantum mechanics and general relativity. Indeed, the ongoing quest for quantum gravity has turned out to be a formidable challenge attacked without success by some of the most brilliant physicists of the last decades. The fact that the experimental signatures of quantum gravity are in most cases orders of magnitude beyond our foreseeable experimental reach does for sure not help in this context. Quantum gravity has been so far the playground of mostly theoretical speculations, though there are hopes that its effects can be probed experimentally in the near future either from cosmological observations or from ultra-high precision measurements of quantum systems. Formulating a theory of quantum gravity would be a massive breakthrough, comparable or even more important than the formulation of quantum mechanics and general relativity themselves.

I encourage the interested reader to take an interactive look at the various mysteries of the Standard Model and the various “Theories of Everything” that have been proposed in this infographic by Quanta Magazine.

In addition, particle physics is much, but really much, broader than just searching for new theories beyond the Standard Model or trying to formulate the theory of quantum gravity. Particle physics is also about achieving an improved understanding of pressing questions within the strong interaction, including how the masses and spin of the hadrons are generated in terms of its constituents, whether or not heavy quarks are part of the proton wave function, the possible onset of extreme dynamical regimes of gluon-dominated matter, or pinning down the properties of the Quark-Gluon Plasma, the hot and dense medium created in the collisions between heavy ions. Anyone who reduces high energy physics to model building is deliberately misleading, and leaving out crucial (and thriving) areas of our field.

One of the main hopes to unravel the next layer of the physical reality is that the thorough exploration of the Higgs boson properties can shed some light on the SM mysteries. For instance, we are now only starting to scratch the surface of the Higgs particle, and current and future measurements at the LHC will tell us more about its underlying nature. Indeed, one of the main goals of the High-Luminosity upgrade of the LHC (HL-LHC), which will deliver up to a factor 10 more collisions, is the accurate profiling of the properties of the Higgs boson, where any deviation with respect to the tightly fixed properties of the SM would represent a “smoking gun” for new physics beyond it. Crucial in this context is the measurement of its self-coupling: not only we have never observed a fundamental scalar particle interacting with itself, it could play a role to explain the matter-antimatter asymmetry in the universe by means of electroweak baryogenesis.

While the HEP community is certainly together in its support for the full exploitation of the physics potential of the HL-LHC as a major priority, it’s less clear what should come next. Should we build yet a bigger particle collider? A different type of collider? Perhaps the key is in the intensity, high-precision frontier? Should we focus on completely different types of experiments, perhaps more weighted towards astrophysics and cosmology? Something else that no one has even thought of before?

In this context, one particularly attractive proposal goes under the name of Future Circular Collider (FCC). The FCC would be a gargantuan particle collider with a radius of around 100 kilometers, dwarfing the already pretty huge LHC. This collider could accelerate protons up to the extreme energies of 100 TeV, about 7 times more powerful than those available at the LHC. In addition, this machine could also accommodate the collisions between electrons and positrons at high energy and luminosity, which would make extremely high precision characterization of SM particles possible, such as the Higgs boson, the W and Z gauge bosons, and the top quarks. Similar machines are under active study by the Chinese HEP community. Another proposal for the next collider is the International Linear Collider (ILC), a high energy linear accelerator of electrons and positrons, to be hosted by Japan.

While it would be amazing if we had machines like those at our disposal, they will come with a hefty price tag, and it is obviously not a decision that can be taken lightly, and the science case in each option must the weighted carefully. One particularly challenging aspect of the current situation for high-energy physics is that there is no machine that can guarantee discoveries, such as new particles or novel fundamental interactions. This was not the case in the past: at the LHC for instance there was a “no-lose” theorem guaranteeing that it would either discover the Higgs boson or instead an altogether novel force of nature. It is worth emphasizing that this is true also for many other fields, such as cosmology, where there is no current or planned experiment that can lead to guaranteed breakthroughs such as evidence for inflation or pinning down the nature of dark energy. The pros and cons of the various proposals for future collider are now being discussed in detail within the community, see for example the recent EPPSU open meeting in Granada.

The bottom line of all this lengthy disquisition is that future progress in HEP should be driven by exploration, rather than by theoretical prejudice, see also Nima Arkani-Hamed’s reflections. For many years (better said, decades) HEP was driven by theoretical efforts, with experiments successfully confirming prediction after prediction. But now our field is experiencing a U-turn, where we should think outside the box and be ready for the unexpected. A nice example of the latter is provided by the recent anomalous in the b-quark sector presented by LHCb. These anomalies seem to indicate the violation of one of the cornerstones of the Standard Model, namely the symmetry telling us that leptons of different families (say muons and electrons) interact with other particles in exactly the same way. Only time will tell the fate of these anomalies, but if confirmed they would represent an arguably more important discovery than that of the Higgs itself!

With the same motivation, and in order to make sure that no stone is left unturned, it is healthy for our field to develop a varied program of experiments that are not limited to high-energy colliders. For instance, CERN has recently set up a Working Group focusing on the potential of ’Physics Beyond Colliders’ (PBC). The idea underlying this approach is that high-precision measurements of specific properties of known particles can reveal the presence of new, heavy particles beyond the direct reach of future colliders. This is possible by means of quantum effects, where heavy virtual particles pop up from the vacuum for a fleeting moment, leaving a measurable imprint in the SM particles.

A prime example of this precision program is shown above: the muon storage ring at Fermilab. There the “muon g-2” experiment aims to measure with exquisite precision the internal magnet of the muons, its so-called magnetic moment. The hope is to resolve a long-standing discrepancy between similar measurements and the SM predictions, which could unveil new physics beyond the SM.

Can we now summarise what the best option is for the future of HEP? Well, not really, this is precisely the million dollar question! Every member of the HEP community, including several popular bloggers within the field, has something important to say there. I think that irrespective of the exact path that our field chooses for the next years, the future is certainly bright for particle physics and everyone should certainly stay tuned for news from the high-energy frontier!

This will hopefully become soon a full fledged personal website and blog, so stay tuned! In the meantime you can contact me via email or find me on Twitter. Some information about myself as well as my contact coordinates can be found here. A brief snapshot of my research interests is also provided, as well as a list of selected talks at seminars, conferences, and workshops.